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18 April 2024 Phylogenetic Classification of Living and Fossil Ray-Finned Fishes (Actinopterygii)
Thomas J. Near, Christine E. Thacker
Author Affiliations +
Abstract

Classification of the tremendous diversity of ray-finned fishes (Actinopterygii) began with the designation of taxonomic groups on the basis of morphological similarity. Starting in the late 1960s morphological phylogenetics became the basis for the classification of Actinopterygii but failed to resolve many relationships, particularly among lineages within the hyperdiverse Percomorpha. The introduction of molecular phylogenetics led to a dramatic reconfiguration of actinopterygian phylogeny. Refined phylogenetic resolution afforded by molecular studies revealed an uneven diversity among actinopterygian lineages, resulting in a proliferation of redundant group names in Linnean-ranked classifications. Here we provide an unranked phylogenetic classification for actinopterygian fishes based on a summary phylogeny of 830 lineages of ray-finned fishes that includes all currently recognized actinopterygian taxonomic families and 287 fossil taxa. We provide phylogenetic definitions for 90 clade names and review seven previously defined names. For each of the 97 clade names, we review the etymology of the clade name, clade species diversity and constituent lineages, clade diagnostic morphological apomorphies, review synonyms, and provide a discussion of the clade's nomenclatural and systematic history. The new classification is free of redundant group names and includes only one new name among the 97 clade names we review and describe, yielding a comprehensive classification that is based explicitly on the phylogeny of ray-finned fishes that has emerged in the 21st century and rests on the foundation of the previous 200 years of research on the systematics of ray-finned fishes.

Introduction

There are currently more than 35,085 described species of ray-finned (Actinopterygii) fishes (Fricke et al. 2023), comprising nearly half of the total living species diversity of vertebrates. The first classifications of the immense diversity of Actinopterygii were the culmination of several important and ambitious surveys of ray-finned and teleost fishes on the basis of comparative anatomy (e.g., Müller 1845a; Cope 1871a, 1871b; T. N. Gill 1872; Goodrich 1909; Jordan 1923; Regan 1929; Garstang 1931; Berg 1940; Greenwood et al. 1966) and morphological studies that were among the first to use cladistic methods (G. J. Nelson 1968, 1969c, 1973; Patterson 1973; Rosen 1973). These early efforts provided support for the monophyly of major clades of Actinopterygii still recognized today, including groups such as sturgeons, gars, tarpons and eels, catfishes, salmons, anglerfishes, tunas, gobies, and flatfishes. However, prior to the application of molecular data, the relationships among many of the major lineages of ray-finned fishes remained unresolved and specific phylogenetic hypotheses relied on the interpretation of a few key morphological characters (e.g., Patterson 1973; Rosen 1973, 1985; Lauder and Liem 1983; Patterson 1993, 1996).

The introduction of molecular data to phylogenetics revolutionized the inference of the tree of life and brought astounding insights, including the paraphyly of Prokaryota (Woese and Fox 1977), the discovery of the inclusive placental mammal lineage Afrotheria (Stanhope et al. 1998), and the resolution of ctenophores as the sister lineage of all other metazoans (C. W. Dunn et al. 2008). In a similar way, molecular data have had an astonishing effect on the resolution of the phylogenetic relationships of Actinopterygii (Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; Miya and Nishida 2015; Hughes et al. 2018; Ghezelayagh et al. 2022; Mu et al. 2022), with nearly every part of the ray-finned fish phylogeny modified as a result of molecular analyses (Dornburg and Near 2021). In the first years of the 21st century, morphology alone was the basis for review papers and authoritative reference texts on the relationships and classification of Actinopterygii (e.g., A. C. Gill and Mooi 2002; Stiassny et al. 2004; J. S. Nelson 2006), indicating the application of molecular data to the phylogenetics of fishes has lagged behind the study of other groups of vertebrates. Given the enormous diversity of Actinopterygii, their ecological divergence throughout nearly every available aquatic habitat, and the variety and extent of their phenotypic disparity, it is unsurprising that morphological studies have been unable to resolve many of the phylogenetic relationships within Actinopterygii.

Over the past 10 years molecular phylogenetics has significantly influenced the classification of Actinopterygii (Near, Eytan, et al. 2012; Wainwright et al. 2012; Near et al. 2013; W. L. Smith et al. 2016; Betancur-R et al. 2017; Dornburg and Near 2021). Studies based on nuclear and mitochondrial gene sequences are now complemented by those using comprehensive datasets of genomic sequences (e.g., Malmstrøm et al. 2016; Arcila et al. 2017; Hughes et al. 2018; Ghezelayagh et al. 2022; Melo, Sidlauskas, et al. 2022; Glass et al. 2023). Phylogenomic data mitigate the issues that may mislead morphological studies; in particular, the data are extremely abundant and there are strategies to detect and accommodate incomplete lineage sorting, introgression, and paralogous loci (Bravo et al. 2019; Simion et al. 2020; M. L. Smith and Hahn 2022). The sheer size of genomic datasets is likely to compensate for random and systematic errors that affect phylogenetic inferences, simply by amplifying a consistent phylogenetic signal over any noise (Simion et al. 2020). Empirical support for this theory would be the repeated inference of the same phylogenetic relationships from different molecular datasets.

As phylogenetic studies of Actinopterygii using larger molecular datasets with inclusive taxonomic sampling became practical, a remarkable result has been the extent to which the molecular phylogenies of ray-finned fishes agree with one another (e.g., Miya et al. 2005; Near, Eytan, et al. 2012; Betancur-R et al. 2017; Chakrabarty et al. 2017; Hughes et al. 2018; Ghezelayagh et al. 2022; Melo, Sidlauskas, et al. 2022). The results of independent phylogenetic analyses are not congruent in every respect, but an overall highly supported phylogeny of Actinopterygii has emerged from analysis of molecular data in the 21st century (Dornburg and Near 2021). The new consensus phylogeny supports traditional relationships such as the resolution of Ostariophysi, Siluriformes, Esocidae, Acanthomorpha, Atheriniformes, Pleuronectoidei, Lophioidei, and Tetraodontoidei as monophyletic groups, but includes relationships not inferred from traditional morphological studies across the entire phylogeny of Actinopterygii (Dornburg and Near 2021). The molecular consensus crucially provides unprecedented resolution in portions of the actinopterygian phylogeny that have been historically difficult to resolve, in particular among lineages of Percomorpha that formerly comprised the largest polytomy in vertebrate phylogenetics (Figure 1; G. J. Nelson 1989; A. C. Gill and Mooi 2002; Dornburg and Near 2021). Molecular phylogenies are also amenable to calibration with fossils to estimate divergence times and evolutionary rates, allowing insight into the mechanisms that generate biodiversity. The known fossil record for Actinopterygii is continually improving (Appendix 1). Fossil-calibrated phylogenies provide estimates of the timing of diversification of ray-finned fishes, placing the origin of Actinopterygii in the Carboniferous (Giles et al. 2017, 2023) and highlighting the Eocene (56.0–33.9 Ma) as an important time in the diversification of percomorph fishes that dominate marine habitats (Ghezelayagh et al. 2022). Such inferences on the timing of lineage diversification would be impossible to resolve with morphological data alone. Instead, we may now use the time-calibrated phylogenies to understand the tempo and patterns of species diversification (e.g., Rincon-Sandoval et al. 2020; Troyer et al. 2022; Friedman and Muñoz 2023) and revisit the abundant, detailed morphological data available and interpret its evolution in the context of evolutionary patterns revealed by genomic-scale phylogenies (e.g., Nakae and Sasaki 2010; Chanet et al. 2013; M. G. Girard et al. 2020).

FIGURE 1.

Comparison of phylogenies and classifications of Acanthomorpha. In the three phylogenies the colors of the branches indicate traditional classifications: red branches are non-percomorph acanthomorphs, orange branches are non-perciform Percomorpha, and blue branches are Perciformes (sensu lato). The phylogeny from A. C. Gill and Mooi (2002) is a summary hypothesis based on morphology. The phylogeny used to show the classifications of Betancur-R et al. (2017) and Dornburg and Near (2021) are based primarily on molecular studies. Numbers in parentheses indicate the number of taxonomic families.

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An important application of a robust phylogeny is to provide the framework for a classification. In the case of Actinopterygii, many of the lineages resolved in the 21st century molecular phylogeny had already been known and named in taxonomies based primarily on morphological inferences (e.g., Bleeker 1859; T. N. Gill 1872; Greenwood et al. 1966; J. S. Nelson 2006). Linnaean ranked classification requires the use of primary taxonomic categories: Actinopterygii is a Linnaean class, containing the ranks of order, family, genus, and species, each of which must be assigned for every taxon. In the Linnaean-ranked classification system of Actinopterygii, 28% of the approximately 515 taxonomic families are monotypic or monogeneric. In these cases, the family-group and genus names are redundant: both names refer to the same group of taxa. Consider the Salamanderfish (Lepidogalaxias salamandroides), which is the sister lineage of a clade containing more than 21,400 species of euteleost fishes (J. Li, Xia, et al. 2010; McDowall and Burridge 2011; Burridge et al. 2012; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; Campbell, López, et al. 2013; Davis et al. 2016; W. L. Smith et al. 2016; Campbell, Alfaro, et al. 2017; Hughes et al. 2018; Straube et al. 2018; Rosas Puchuri 2021; Mu et al. 2022). In the Linnaean rank-based classification, L. salamandroides is classified as the only species in the family Lepidogalaxiidae, which is the only family in the order Lepidogalaxiiformes, which is the only order in the subcohort Lepidogalaxii (Betancur-R et al. 2017). In this taxonomy, Lepidogalaxias, Lepidogalaxiidae, Lepidogalaxiiformes, and Lepidogalaxii all have the same composition. Using these nested ranks to include the single species Lepidogalaxias salamandroides conveys no information and only lists several redundant group names.

An alternative to the Linnaean system is the unranked phylogenetically-based taxonomy outlined in the PhyloCode (Cantino and de Queiroz 2020). Use of the PhyloCode system prevents the proliferation of unnecessary and redundant group names and avoids the unsupported preconception that ranked categories have meaning apart from their exclusivity (de Queiroz and Gauthier 1990, 1992, 1994). In other words, it is easy to overlook that family-ranked taxa are not comparable to one another in any biologically or evolutionarily significant way; all a ranked taxon indicates is that any species within it are not included in any other taxon of equivalent rank. The PhyloCode is also strictly phylogenetic, a desirable characteristic that gives meaning to group names by explicitly tying them to clades. Clades in the PhyloCode are defined phylogenetically, differing from traditional Linnaean group names in they are defined in terms of ancestry and descent rather than being defined in terms of ranks and types. Each clade name is defined by at least two reference points on a phylogeny, either two taxa or a taxon and an apomorphy. The formulation of such phylogenetic definitions requires a comprehensive phylogenetic hypothesis. For Actinopterygii, such a hypothesis is now available, allowing for a transformation of the traditional classification of ray-finned fishes into a strictly phylogenetic framework that is as free as possible from redundant group names.

A landmark and ambitious Linnaean-ranked classification of Actinopterygii based on a phylogeny inferred from mtDNA and nuclear genes led to a proliferation of taxonomic orders and redundant group names (Betancur-R, Broughton, et al. 2013; Betancur-R et al. 2017). The proliferation of group names in Betancur-R et al. (2017) was a consequence of an effort to preserve traditional ordinal ranks for percomorph clades such as Pleuronectiformes, Tetraodontiformes, Mugiliformes, and Cyprinodontiformes. Because of their morphological disparity, these lineages were traditionally classified as taxonomic orders (e.g., A. C. Gill and Mooi 2002), set apart from the wastebin taxon Perciformes in morphology-based efforts (Figure 1). Molecular phylogenies resulted in the dramatic reallocation of lineages traditionally classified as Perciformes into nearly every major clade of Percomorpha (Figure 1), pushing traditional taxonomic orders such as Tetraodontiformes, Gobiesociformes, and Synbranchiformes from deeply nested positions into more apical resolutions in the phylogeny of Percomorpha. Within Percomorpha, the Betancur-R et al. (2017) classification delimits 34 taxonomic orders, each containing an average of only 7.4 taxonomic families; 13 of the 34 taxonomic orders contain only one or two families and only 10 of the orders have 10 or more families. In addition to delimiting less inclusive groups, the Betancur-R et al. (2017) classification treats 10% of all percomorph families as incertae sedis (Figure 1). The phylogenetic rank-free classification presented here delimits 16 major clades in Percomorpha, 13 of which are consistent with traditional taxonomic orders and contain an average of 21.8 lineages each that are treated as taxonomic families in rank-based classifications (Figure 1, Appendix 2; Dornburg and Near 2021; Ghezelayagh et al. 2022). The effort to maintain a handful of traditional taxonomic orders in Percomorpha in the Betancur-R et al. (2017) classification has resulted in a proliferation of “-iformes” group names that are neither inclusive nor phylogenetically informative (Figure 1).

Our goal in constructing a new rank-free classification of Actinopterygii is to build on and unify the punctuated progress made in the phylogenetics of ray-finned fishes in the 21st century (Dornburg and Near 2021). In this monograph, we consolidate and review the history of systematics and phylogenetics of the primary clades of ray-finned fishes, provide phylogenetic definitions for the names of 97 actinopterygian clades, introduce a summary phylogeny of 830 ray-finned fish lineages that includes 287 fossil taxa (Appendix 1), review information on species diversity in each clade, and provide a comprehensive list of constituent lineages for every major actinopterygian clade. We explicitly incorporate available phylogenies and whenever possible list diagnostic morphological apomorphies for each named clade. The new rank-free classification avoids redundant group names and attempts to preserve the exclusivity of clade names with -iformes, -oidei, and -oidea suffixes. For instance, clade names with an -iformes suffix are not nested in any other clade with a name ending in -iformes. In the phylogenetic trees, we list the genus name or the species binomial if a taxonomic family contains a single genus or species. In the clade accounts, we acknowledge the long history of the use of taxonomic families in ichthyology, listing all recognized taxonomic families but indicating those that are monotypic or monogeneric by identifying them with an asterisk as a redundant group name.

This new rank-free classification of Actinopterygii consolidates and reviews the systematic ichthyology literature of the past two centuries, builds on a consensus phylogenetic hypothesis of actinopterygian relationships, and constructs an explicit phylogenetic-based taxonomy that aims to be useful and flexible for researchers now and in the future. With this comprehensive phylogeny and classification, it is possible to investigate and communicate the overarching patterns of evolution within ray-finned fishes, which are rich in morphological complexity, ecological diversity, and biogeographic range. Combined with advances in comparative analyses that use time-calibrated molecular phylogenies, we are beginning to understand the tempo and characteristics of vertebrate evolution in aquatic habitats, across oceans and rivers, at the poles and the tropics, on coral reefs, and in environments from shallow shores to abyssal depths (e.g., Tedesco et al. 2017; Rabosky et al. 2018; Rincon-Sandoval et al. 2020; Melo, Sidlauskas, et al. 2022; E. C. Miller et al. 2022; Friedman and Muñoz 2023).

Materials and Methods

We develop a phylogeny-based classification of Actinopterygii following the principles of phylogenetic nomenclature outlined in the PhyloCode (de Queiroz and Gauthier 1990, 1992, 1994; Cantino and de Queiroz 2020), except where indicated. Articles (Art.), examples (Ex.), and recommendations (Rec.) are referred to as outlined in the International Code of Phylogenetic Nomenclature (PhyloCode) ver. 6 (Cantino and de Queiroz 2020). Following Rec. 6.1A, all scientific names of clades are italicized. This differs from the customary practice of only italicizing the genus and species names. Most of the clades presented and reviewed in this monograph are defined as minimum-crown-clades that have at minimum two internal specifiers that are both extant (Arts. 9.5 and 9.9). If there is uncertainty about the early branching history of a well-established clade, more than two specifiers are used (Art. 9.5). In a few instances, external specifiers (Art. 11.13, Ex. 1) are used to prevent the use of a clade name under specific phylogenetic hypotheses.

In following the requirements for establishing clade names (Art. 7), we provide a protologue (Art. 7.2, N. 7.2.1) for each clade name that provides everything associated with the name as it is established according to the requirements of the PhyloCode. The terms protologue and clade account are used interchangeably in this monograph. In this classification of Actinopterygii each protologue contains 10 sections.

The definition is the statement that explicitly identifies a clade as the referent of the taxon name and includes at least two specifiers (Art. 9.4). Original author citations are provided for each specifier.

Etymology is an attempt to trace the linguistic origin of clade names. Most of the clade names originate in ancient Greek, and we provide the original spelling following reference texts (D. W. Thompson 1947; Liddell et al. 1968). When the original spelling is ancient Greek, we provide a phonetic spelling of the word using the International Phonetic Alphabet (IPA 1999).

The registration number is the product of the required submission of the clade name to the official registration database (Art. 8.1). All the clade names and associated information tied to the clade definitions were submitted to the online RegNum database (Cellinese and Dell 2020), which is the official registry of clade names in PhyloCode. No registration number is given for the 11 clades that are not defined using the PhyloCode.

The reference phylogeny is a specific phylogenetic hypothesis that provides the basis and context for applying a clade name in the phylogenetic definition (Art. 7.2). The reference phylogenies were selected on the basis of taxonomic coverage and the inclusion of appropriate specifiers. Phylogenies resulting from an explicit and reproduceable analysis were the only ones considered (Rec. 9.13A). The reference phylogenies come from a total of 34 phylogenetic studies. Among the 97 clade accounts, the reference phylogeny for 46 clades are based on analysis of genomic data, 33 are based on analyses of Sanger-sequenced molecular data, 11 clades are defined using phylogenies inferred from combined molecular and morphological datasets, and seven clades are defined on the basis of phylogenies inferred from morphological characters alone. A synthetic phylogeny of 830 lineages of Actinopterygii was constructed using published phylogenetic trees in an agglomerative procedure (Beaulieu et al. 2012). All the phylogenetic studies used to construct the synthetic tree are cited among the clade accounts. The tree file in Newick is available at the Dryad data repository (Near and Thacker 2023). In the reference phylogeny section, we refer to the figure number in this monograph where the relationships of a given clade are shown and citations are provided to justify the placement of any fossil taxa in the phylogenies (Appendix 1). The absolute age intervals of the epochs, ages, and stages of the fossil record follow the Geologic Time Scale 2020 (Gradstein and Ogg 2020). In the phylogenetics section we provide a brief history of the systematics of the clade. Often this is the longest section of the clade account.

The composition of the clade includes a statement as to the current recognized species diversity and a listing of all the named major subclades of the named clade. There are no redundant group names listed in this section. If a taxonomic family in the Linnaean ranked system is monotypic or monogeneric, the species binomial or the genus name is provided. The names of fossil taxa within each named clade that are not nested in a subclade not defined in the classification are included in the phylogenetic trees and listed in the clade composition. We also highlight recent biodiversity discoveries by listing the number of new species described over the past 10 years (2013–2023).

Diagnostic apomorphies lists morphological traits that investigators have offered as diagnostic for the clade. While not required to establish a clade name in PhyloCode, we acknowledge the rich history of morphological phylogenetics in ichthyology that has resulted in hypothesized morphological synapomorphies for many of the clades reviewed here. In providing this information we make no judgment on the veracity of the characters but rely on dozens of studies that list morphological characters as diagnostic for the clades named and reviewed here.

A synonym is a name that has a spelling that is different from another name that refers to the same taxon (Art. 14.1). We differentiate three types of synonyms. Ambiguous synonyms are two names that are spelled differently for the same clade with the same taxa contained in that clade but were not given explicit phylogenetic definitions. Approximate synonyms are very close to the same clade and the content may slightly differ. Partial synonyms could be names for paraphyletic groups that exclude a part of the crown or other examples where some portion of the defined clade content is not included in the group delimited by the partial synonym.

The comments section provides space to discuss aspects of the phylogenetics or biology of a clade that merit highlighting. In addition, we attempt to list the earliest fossil occurrences of the clade and provide information on any molecular age estimate for the lineage.

The constituent lineages section provides a tabulation of all the major taxa comprising the defined clade. Any taxonomic families listed that are monotypic or monogeneric are marked with an asterisk as redundant group names. All names that are defined as clade names or listed in a protologue that have the suffix of -oidea, -idae, -inae, or -ini are valid family-group names under the International Code of Zoological Nomenclature (Van der Laan et al. 2014).

Our approach to constructing a rank-free classification of Actinopterygii necessitated a slight deviation from the principles and rules of the PhyloCode. While committed to maximizing the benefits of a classification that avoids redundant names, we have chosen a tempered approach that aims to accommodate traditional aspects of systematic ichthyology. Our classification is fully rank-free, but we use names with suffixes that include -formes, -oidei, and -oidea that are traditionally used for ranks of order, suborder, and superfamily. In avoiding the nesting of group names with the same suffixes, we maintain the exclusivity of those names, which requires replacement of the suffixes of several names in current usage. For example, we use Lophioidei and Tetraodontoidei in favor of Lophiiformes and Tetraodontiformes to avoid nesting these groups in Acanthuriformes. Because this is counter to PhyloCode's Principle 4 on stability, we do not use the PhyloCode in defining Gadoidei, Atheriniformes, Atherinoidei, Belonoidei, Cyprinodontoidei, Pleuronectoidei, Lophioidei, and Tetraodontoidei. We also do not use the PhyloCode in defining Salmoniformes, Esocidae, and Gadiformes because our delimitations of these groups would require the application of new group names.

In this classification we aim to preserve the nomenclatural history of actinopterygian systematics by retaining preexisting names for clades as much as possible. Among the 97 clade names in this classification, only one (Oseanacephala) is new and only seven other clade names date to the 21st century (Acropomatiformes, Apogonoidei, Cithariniformes, Eupercaria, Ovalentaria, Stomiatii, and Zoarcoidea). Forty-five of the group names were introduced from 1700 to 1900 CE, 19 names date from 1901 to 1950 CE, 25 group names were introduced between 1951 and 2000 CE, and 8 group names date from 2001 to 2022 CE. Seven of the 97 clade definitions were initially published in the PhyloCode companion volume (de Queiroz et al. 2020b; Lundberg 2020a, 2020b, 2020d; Moore and Near 2020a, 2020b, 2020c, 2020f) and are included here with any additional information to make the accounts uniform with the 90 new clade accounts.

Clade Accounts

Actinopterygii A. S. Woodward 1891:423
[J. A. Moore and T. J. Near 2020b]

  • Definition. Defined as a minimum-crown-clade by Moore and Near (2020b) as: “The least inclusive crown clade that contains Polypterus bichir Lacépède 1803, Acipenser sturio Linnaeus 1758, Psephurus gladius (Martens 1862), Lepisosteus osseus (Linnaeus 1758), Amia calva Linnaeus 1766, and Perca fluviatilis Linnaeus 1758.”

  • Etymology. From the ancient Greek ἀκτίς (̍æktIs), meaning ray or beam, and πτερὀν (t̍εɹαːn), meaning fin or wing.

  • Registration number. 206.

  • Reference phylogeny. Diogo (2007, figs. 3, 4) was designated as the primary reference phylogeny by Moore and Near (2020b). See Figures 2 and 3 for a summary phylogeny of major clades in Actinopterygii. The placement of †Scanilepiformes is supported in phylogenetic analyses of morphological characters (Giles et al. 2017, 2023; Latimer and Giles 2018).

  • Phylogenetics. The earliest phylogenetic investigations of Actinopterygii involved the secondary mapping of morphological character state changes onto tree topologies that placed Polypteridae (bichirs and ropefish) as the sister group of Actinopteri (e.g., Rosen et al. 1981; Patterson 1982; Lauder and Liem 1983; Gardiner 1984). The earliest phylogenetic analyses of morphological data matrices resolved Polypteridae as an actinopterygian and placed several Devonian fossil taxa (e.g., †Mimia, †Howqualepis, †Moythomasia, and †Kentuckia) as crown lineage Actinopterygii (Gardiner and Schaeffer 1989; Coates 1999; Gardiner et al. 2005; Xu, Gao, et al. 2014; Caron et al. 2023). The status of these Devonian taxa as crown clade actinopterygians was dramatically overturned by more recent morphological phylogenetic analyses that resolve numerous Devonian-Triassic taxa as stem lineage actinopterygians and place Polypteridae as nested within the Triassic-aged pan-scanilepiforms or as the sister group of †Scanilepiformes (Giles et al. 2017, 2023; Argyriou et al. 2018, 2022; Latimer and Giles 2018; Ren and Xu 2021). From the first molecular phylogenetic studies of ray-finned fishes to the most recent phylogenomic studies (e.g., Normark et al. 1991; Hughes et al. 2018), Actinopterygii is resolved as monophyletic with Polypteridae as the sister lineage of Actinopteri (Inoue et al. 2003a; Kikugawa et al. 2004; Alfaro, Santini, et al. 2009; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; M.-Y. Chen et al. 2015; Hughes et al. 2018; Vialle et al. 2018; Wcisel et al. 2020; Bi et al. 2021). In contrast to the consistent resolution of Polypteridae as the sister lineage of all other living Actinopterygii in molecular studies, some morphological phylogenetic analyses that include fossil taxa resolve a clade with low node support containing Polypteridae, †Scanilepiformes, pan-acipenseriforms, and Acipenseriformes (Argyriou et al. 2018; Latimer and Giles 2018; Caron et al. 2023; Giles et al. 2023).

  • Composition. Actinopterygii includes more than 35,085 living species (Fricke et al. 2023) classified in Polypteridae and Actinopteri. Fossil taxa within Actinopterygii include †Scanilepiformes (Appendix 1; Sytchevskaya 1999; Xu and Gao 2011; Giles et al. 2017). Appendix 1 provides details of the ages and locations of the fossil scanilepiforms. Over the past 10 years 3,657 new living species of Actinopterygii have been described (Fricke et al. 2023), comprising 10.4% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Actinopterygii include (1) cerebellum with corpus cerebelli, auricle, and valvula (Gardiner 1973; Løvtrup 1977:175), (2) teeth with apical cap of acrodin (Ørvig 1978; Rosen et al. 1981; Patterson 1982), (3) absence of superficial constrictors on gill arches (Wiley 1979), (4) presence of obliqui ventrales branchial muscle (Wiley 1979), (5) origin of coracomandibularis on branchial arch 3 (Wiley 1979), (6) adductor operculi continuous with adductor hyomandibulae (Lauder 1980), (7) adductor arcus palatini absent (Lauder 1980), (8) pelvic plate and two series of radials present (Patterson 1982), (9) anterodorsal process on scales (Patterson 1982), (10) a slender peg-and-socket articulation between scales (Patterson 1982), (11) autosphenotic ossified in postorbital process, autosphenotic and dermosphenotic fused (Patterson 1982), (12) single hyomandibular articulation above jugal canal (Patterson 1982), (13) postcleithrum present (Patterson 1982; Coates 1998), (14) prismatic ganoine on scales (Gardiner and Schaeffer 1989; Coates 1999), (15) three or more supraorbitals (Giles et al. 2017), (16) one or two infradentaries (Giles et al. 2017), (17) coronoid process of lower jaw present (Giles et al. 2017), (18) palatoquadrate with separate centers of ossification (Giles et al. 2017), (19) palate with flat dorsal margin (Giles et al. 2017), (20) narrow interorbital septum (Giles et al. 2017), (21) roof of posterior myodome perforated by palatine branch of facial nerve (Giles et al. 2017), (22) median posterior myodome present (Giles et al. 2017), (23) dermal component to basipterygoid process present (Giles et al. 2017), (24) parasphenoid extends to basioccipital (Giles et al. 2017), (25) ascending process of parasphenoid process present (Giles et al. 2017), (26) proximal segments of pectoral fin elongate with terminal segmentation (Giles et al. 2017); (27) proximal radials of dorsal fin enlarged (Giles et al. 2017); (28) constrictor mandibularis dorsalis attaches to the hyoid arch (Datovo and Rizzato 2018); and (29) constrictor mandibularis has an insertion on the lateral face of the palatoquadrate (Datovo and Rizzato 2018).

  • Synonyms. There are no synonyms of Actinopterygii.

  • Comments. Actinopterygii represents one of the major lineages of living vertebrates and along with Sarcopterygii comprises Osteichthyes (Rosen et al. 1981; Stiassny et al. 2004; Bertrand and Escrivá 2014; Moore and Near 2020d). When Actinopterygii was first introduced as a group name it excluded Polypteridae and had a composition identical to Actinopteri (Woodward 1891:423). Citing evidence from the morphology of scales, dermal bones of the head, the skull, nostrils, median fins, and paired fins and girdles, Goodrich (1928) considered Polypteridae as a group within Actinopterygii. By the 1980s the concept of Actinopterygii as comprising Polypteridae and Actinopteri was solidified in studies and reviews of morphological evidence (Rosen et al. 1981; Patterson 1982).

  • The earliest actinopterygian fossil taxon is †Platysomus superbus from the Visean (346.7–330.0 Ma) in the Carboniferous of Scotland, UK (C. D. Wilson et al. 2021). The inferred phylogenetic relationships of †Platysomus vary among morphological studies, but the taxon is consistently resolved as a lineage of Actinopterygii (Giles et al. 2017, 2023; Argyriou et al. 2018, 2022; Latimer and Giles 2018). Bayesian relaxed molecular clock age estimates for the crown age of Actinopterygii range between 333.5 and 384.1 million years ago, extending across the Devonian-Carboniferous boundary (Giles et al. 2017).

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    FIGURE 2.

    Phylogenetic relationships of the major living lineages of Actinopterygii, Actinopteri, Neopterygii, Teleostei, Oseanacephala, Clupeocephala, Otocephala, Ostariophysi, Otophysi, Euteleostei, Salmoniformes, Stomiatii, Neoteleostei, Ctenosquamata, Acanthomorpha, Paracanthopterygii, Gadiformes, Acanthopterygii, Percomorpha, Ovalentaria, and Eupercaria. Filled circles identify the common ancestor of clades, with formal names defined in the clade accounts.

    img-z9-1_03.jpg

    FIGURE 3.

    Phylogenetic relationships of the major living lineages and fossil taxa of Actinopterygii, Actinopteri, Neopterygii, Pan-Teleostei, and Teleostei. Filled circles identify the common ancestor of clades, with formal names defined in the clade accounts. Open circles highlight clades with informal group names. Fossil lineages are indicated with a dagger (†). Details of the fossil taxa are presented in Appendix 1. The clade description of Pan-Teleostei is presented in Moore and Near (2020e). The illustration of †Leptolepis coryphaenoides is reproduced with permission from Arratia (1996b).

    img-z10-1_03.jpg

    Polypteridae C. L. Bonaparte 1835
    [in Bonaparte 1840]:188–189
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive clade that contains Erpetoichthys calabaricus J. A. Smith 1865:2 and Polypterus bichir Lacepède 1803. This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek πoυλύς (p̍uːlәs), meaning many, and πτερόν (tˈɛɹɑːn), meaning wing.

  • Registration number. 851.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of eight concatenated Sanger-sequenced nuclear genes (Near, Dornburg, Tokita, et al. 2014, fig. 1). A phylogeny of all species of Polypteridae is shown in Figure 4.

  • Phylogenetics. All species of Polypteridae are included in phylogenies inferred from mtDNA and Sanger-sequenced nuclear genes (Figure 4; Suzuki et al. 2010; Near, Dornburg, Tokita, et al. 2014).

  • Composition. There are currently 14 living species of Polypteridae that includes Erpetoichthys calabaricus and 13 species of Polypterus (Moritz and Britz 2019). Over the past 10 years no new living species of Polypteridae have been described (Fricke et al. 2023).

  • Diagnostic apomorphies. Morphological apomorphies for Polypteridae include (1) larvae with external gills that originate outside the branchial cavity (Daget 1950; Stundl et al. 2019), (2) single basibranchial (Jarvik 1980; Carvalho et al. 2013), (3) separate dorsal finlets (Daget 1950; Jarvik 1980; Gardiner and Schaeffer 1989; Coelho et al. 2018), (4) putative dorsal ribs (Britz and Bartsch 2003), (5) occipital bone that articulates posteriorly with centrum of second vertebra (Britz and Johnson 2010), (6) spiracular canal absent (Gardiner et al. 2005), (7) ascending process of parasphenoid fused to otic region and not related to spiracle (Gardiner et al. 2005), (8) parasphenoid with aortic canal (Gardiner et al. 2005), (9) parietals absent, dermopterotics meet (Gardiner et al. 2005), (10) maxilla with superimposed infraorbital canal and dorsal arm of preopercular greatly expanded (Gardiner et al. 2005), (11) coronoid process of lower jaw composed exclusively of prearticular (Gardiner et al. 2005; Giles et al. 2017), (12) optic foramen adjacent to dorsal margin of parasphenoid (Giles et al. 2017), (13) broad interorbital septum (Giles et al. 2017), (14) lateral process present on ectopterygoid (L. Grande 2010; Giles et al. 2017), (15) four ceratobranchials (Britz and Johnson 2003; Giles et al. 2017), (16) loss of fulcra of caudal fin (Patterson 1982; Giles et al. 2017), (17) three pairs of extrascapulars (Gardiner and Schaeffer 1989; Giles et al. 2017), and (18) constrictor mandibularis dorsalis, levator arcus palatini is differentiated into partes interna and externa (Datovo and Rizzato 2018).

  • Synonyms. Brachiopterygii (G. J. Nelson 1969a, fig. 25), Cladistia (Rosen et al. 1981, fig. 62; Betancur-R et al. 2017:9), and Polypteriformes (J. S. Nelson et al. 2016:116; Betancur-R et al. 2017:9) are ambiguous synonyms of Polypteridae.

  • Comments. Bonaparte (1840) applied the group name Polypterini as a subfamily of Lepidosteidae, which is a synonym of Lepisosteidae. The delimitation of Polypteridae as containing Polypterus and Erpetoichthys calabaricus presented here was frequently used by ichthyologists in the second half of the 19th though the early 20th century (Günther 1870:326–331, 1880:364; Bridge 1904:481–485; Boulenger 1909:4; Goodrich 1909:300). We selected the name Polypteridae as the clade name over its synonyms because it is the name most frequently applied to a taxon approximating the named clade. Polypteridae is the living sister lineage of all other actinopterygians (Actinopteri) and results from relaxed molecular clock analyses that estimate the common ancestry of these two lineages dates to an interval between 333.5 and 384.1 million years ago (Giles et al. 2017).

  • In contrast to the ancient divergence of Polypteridae and Actinopteri, the earliest pan-polypterid fossils date to the Cenomanian (100.5–93.9 Ma) of the Upper Cretaceous (Daget et al. 2001; Gayet et al. 2002; Near, Dornburg, Tokita, et al. 2014), implying a gap in the fossil record of polypterids that spans at least 240 million years. All extant species of Polypteridae live in the freshwaters of western and central Africa, although pan-polypterid fossils are known from both Africa and South America (Gayet and Meunier 1991, 1992; Meunier and Gayet 1996; Daget et al. 2001; Otero et al. 2009). Time-calibrated multi-species coalescent analyses estimate a relatively recent time to common ancestry for the living species of Polypteridae, spanning the Miocene and early Oligocene between 13.6 and 24.9 million years ago (Near, Dornburg, Tokita, et al. 2014). Polypteridae is a valid family-group name under the International Code of Zoological Nomenclature (Van der Laan et al. 2014:27).

  • img-z13-6_03.gif

    FIGURE 4.

    Phylogenetic relationships of the species of Polypteridae. Filled circles identify the common ancestor of clades, with formal names defined in the clade accounts.

    img-z12-1_03.jpg

    Actinopteri E. D. Cope 1871:587
    [J. A. Moore and T. J. Near 2020]

  • Definition. Defined as a minimum-crown-clade by Moore and Near (2020a) as: “The least inclusive crown clade that contains Acipenser sturio Linnaeus 1758, Psephurus gladius (Martens 1862), Lepisosteus osseus (Linnaeus 1758), Amia calva Linnaeus 1766, and Perca fluviatilis Linnaeus 1758.”

  • Etymology. From the ancient Greek πουλύς (̍æktIs), meaning ray or beam, and πτερόν (tˈɛɹɑːn), meaning fin or wing.

  • Registration number. 208.

  • Reference phylogeny. Diogo (2007, figs. 3, 4) was designated as the primary reference phylogeny by Moore and Near (2020a). See Figures 2 and 3 for summary phylogenies of major clades in Actinopteri. The placements of the stem-acipenseriforms †Pycnodontiformes, †Guildayichthyidae, †Bobasatraniidae, †Australosomus, †Redfieldiidae, †Platysiagidae, †Dipteronotus, †Peltopleuridae, †Thoracopteridae, †Venusichthys, and †Habroichthys are on the basis of phylogenetic analyses of morphological characters (L. Grande and Bemis 1991, 1996; Bemis et al. 1997; Lund 2000; Hilton and Forey 2009; Mickle et al. 2009; Hilton et al. 2011; Xu et al. 2012; Poyato-Ariza 2015; Xu and Ma 2016; Xu and Zhao 2016; Giles et al. 2017, 2023; Xu 2021; Shedko 2022; Yuan et al. 2022).

  • Phylogenetics. The earliest phylogenetic investigations of Actinopteri involved the secondary mapping of morphological character state changes onto tree topologies that placed chondrosteans (Acipenseriformes) and Neopterygii (Holostei and Teleostei) as sister lineages (Rosen et al. 1981; Patterson 1982; Lauder and Liem 1983; Gardiner 1984). Phylogenetic analyses of morphological data matrices corroborate the monophyly of Actinopteri (Coates 1999; Gardiner et al. 2005; Xu, Gao, et al. 2014; Poyato-Ariza 2015; Giles et al. 2017; Latimer and Giles 2018). Several molecular studies ranging from analyses of whole mtDNA genomes, samples of Sanger-sequenced nuclear genes, and phylogenomic analyses resolve Actinopteri as a monophyletic group (Inoue et al. 2003a; Kikugawa et al. 2004; Alfaro, Santini, et al. 2009; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; M.-Y. Chen et al. 2015; Hughes et al. 2018; Vialle et al. 2018; Wcisel et al. 2020; Bi et al. 2021; Mu et al. 2022).

  • Composition. Actinopteri includes 35,075 living species classified in the subclades Acipenseriformes and Neopterygii. Fossil taxa within Actinopteri include the pan-acipenseriforms †Boreosomus, †Chondrosteus, and †Peipiaosteus; and the pan-neopterygians †Australosomus, †Bobasatraniidae, †Dipteronotus, †Guildayichthyidae, †Habroichthys, †Peltopleuridae, †Platysiagidae, †Pycnodontiformes, †Redfieldiidae, †Thoracopteridae, and †Venusichthys. Details of the ages and locations of the fossil taxa are presented in Appendix 1. Over the past 10 years 3,675 new living species of Actinopteri have been described (Fricke et al. 2023), comprising 10.4% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Actinopteri include (1) perforated propterygium (Patterson 1982), (2) bases of marginal rays or pectoral fin embracing propterygium (Patterson 1982), (3) basal fulcra on dorsal margin of caudal fin (Patterson 1982), (4) fringing fulcra on median fins (Patterson 1982), (5) supra-angular bone present on lower jaw (G. J. Nelson 1973; Patterson 1982), (6) presence of spiracular canal in braincase (Patterson 1982), (7) swim bladder with dorsal connection to foregut (Patterson 1982), (8) hemopoietic organ above medulla (Patterson 1982), (9) diffuse pancreas (Patterson 1982), (10) olfactory rosette (Patterson 1982), (11) supratemporal fused with intertemporal forming dermopteric (Coates 1999), (12) fewer than 12 or 13 branchiostegal rays or plates (Coates 1999), (13) posterior parasphenoid expanded to cover ventral otic fissure (Coates 1999), (14) post-temporal fossa (Xu, Gao, et al. 2014), (15) basipterygoid process absent (Xu, Gao, et al. 2014), (16) quadratojugal overlaying quadrate (Xu, Gao, et al. 2014), (17) loss of presupracleithrum (Xu, Gao, et al. 2014), (18) dorsal aorta open in groove (Giles et al. 2017), (19) cerebellar corpus undivided (Giles et al. 2017), (20) cerebellar corpus with median anterior projecting portion (Giles et al. 2017), (21) hour-glass shaped medial constriction of anterior ossification of ceratohyal (Giles et al. 2017), and (22) uncinate processes on epibranchials (Giles et al. 2017).

  • Synonyms. Actinopterygii as delimited in Boulenger (1891:10), Woodward (1891:423), Dean (1895:8), McAllister (1968:18–20), G. J. Nelson (1969a:534), J. S. Nelson (1976:58; 1984:77–78) Løvtrup (1977:170–176), and Forey (1980:378) excluded Polypteridae and is therefore an approximate synonym of Actinopteri. Garstang (1931:255–256) introduced the group name Epipneusta, containing Acipenseriformes, Holostei, and Teleostei; Epipneusta is an approximate synonym of Actinopteri.

  • Comments. Cope's (1871b) first delimitation of Actinopteri included Acipenseriformes, Holostei, and Teleostei and is identical to the composition of the clade described here. Later Cope (1877b) modified Actinopteri to include only Holostei and Teleostei, but subsequent classifications used Cope's (1871b) initial concept of Actinopteri to include Acipenseriformes, Holostei, and Teleostei (Jordan 1905; Gregory 1907). After the application of phylogenetic systematics to the study of ray-finned fishes, Actinopteri was reintroduced to include all living actinopterygians except Polypteridae (Patterson 1982). The earliest fossils of Actinopteri are the pan-neopterygian guildayichthyids †Discoserra pectinodon and †Guildayichthys carnegiei from the Serpukhovian (330.3–323.4 Ma) in the Carboniferous of Montana, USA (Lund 2000; Mickle et al. 2009). Bayesian relaxed molecular clock analyses estimate a crown age of Actinopteri between 309 and 357 million years ago (Giles et al. 2017).

  • img-z15-2_03.gif

    Acipenseriformes L. S. Berg 1940:408–409
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Acipenser sturio Linnaeus 1758 and Polyodon spathula (Walbaum 1792). This is a minimum-crown-clade definition.

  • Etymology. Acipenser is the Latin name for sturgeon, which is derived from the ancient Greekἀκκιπἠσιoς (D. W. Thompson 1947). The suffix is from the Latin forma, meaning form, figure, or appearance.

  • Registration number. 879.

  • Reference phylogeny. A phylogeny inferred from a dataset of combined molecular and morphological characters (Shedko 2022, fig. 1). See Figures 2 and 3 for the relationship of Acipenseriformes among the major lineages of Actinopterygii. See Figure 5A for a summary phylogeny of the major lineages of Acipenseriformes. Placements of the fossil acipenseriform taxa in the phylogeny are based on the results of morphological phylogenetic analyses (L. Grande and Bemis 1991, 1996; Bemis et al. 1997; Hilton and Forey 2009; Hilton et al. 2011).

  • Phylogenetics. The earliest phylogenetic trees that show a monophyletic Acipenseriformes were inferred from a distribution of derived character states without an analysis of a coded character data matrix using an explicit optimality criterion (e.g., G. J. Nelson 1969a; Lauder and Liem 1983). Morphological and molecular phylogenies consistently resolve Acipenseriformes as monophyletic (e.g., L. Grande and Bemis 1996; Inoue et al. 2003a; Artyukhin 2006; Alfaro, Santini, et al. 2009; Hilton and Forey 2009; Broughton 2010; Hilton et al. 2011; Near, Eytan, et al. 2012; Giles et al. 2017, 2023; Hughes et al. 2018; Y. Shen et al. 2020; Shedko 2022).

  • Composition. Acipenseriformes includes 28 living species (Fricke et al. 2023) classified in Acipenseridae and Polyodontidae. The number of living species does not include the recently declared extinct Chinese Paddlefish, Psephurus gladius (H. Zhang et al. 2020). The fossil taxa †Protopsephurus and †Paleopsephurus are resolved in morphological phylogenies as pan-polyodontids, that is, outside of the crown clade Polyodontidae (L. Grande and Bemis 1991, 1996). †Priscosturion is resolved as either a pan-acipenserid or nested within Acipenseridae as the sister lineage of Scaphirhynchus (L. Grande and Hilton 2006; Hilton et al. 2011; Shedko 2022; Murray et al. 2023). Details of the ages and locations of the fossil taxa are presented in Appendix 1. Over the past 10 years no new living species of Acipenseriformes have been described (Fricke et al. 2023).

  • Diagnostic apomorphies. Morphological apomorphies for Acipenseriformes include (1) loss of opercle (L. Grande and Bemis 1996; Bemis et al. 1997), (2) fewer than four branchiostegal rays (L. Grande and Bemis 1996; Bemis et al. 1997), (3) endocranium with extensive rostrum (L. Grande and Bemis 1996; Bemis et al. 1997), (4) dorsal and ventral rostral bones (L. Grande and Bemis 1996; Bemis et al. 1997; Hilton et al. 2011), (5) posttemporal bone with a ventral process (L. Grande and Bemis 1996; Bemis et al. 1997), and (6) absence of constrictor mandibularis dorsalis connection to palatoquadrate (Datovo and Rizzato 2018).

  • Synonyms. Acipenseroidei (L. Grande and Bemis 1991:113, 1996:107; Bemis et al. 1997:51–53) is an ambiguous synonym of Acipenseriformes.

  • Comments. Berg (1940) originally included Acipenseridae, Polyodontidae, and †Chondrostei in Acipenseriformes, which we selected as the clade name over its synonyms because it is the name most frequently applied to a taxon approximating the named clade. Morphological phylogenies resolve †Chondrostei and †Peipiaosteidae as pan-acipenseriforms and are not included in Acipenseriformes as delimited here (L. Grande and Bemis 1991, 1996; Hilton and Forey 2009; Hilton et al. 2011). The earliest fossil Acipenseriformes is the pan-polyodontid †Protopsephurus liui from the Barremian (126.5–121.4 Ma) in the Cretaceous of China (Appendix 1). Bayesian relaxed molecular clock analyses of Acipenseriformes result in an average posterior crown age estimate of 126.8 million years ago, with the credible interval ranging between 120.9 and 144.5 million years ago (Hughes et al. 2018).

  • img-z17-2_03.gif

    FIGURE 5.

    Phylogenetic relationships of the major living lineages and fossil taxa of (A) Acipenseriformes and (B) Holostei. Filled circles identify the common ancestor of clades, with formal names defined in the clade accounts. Open circles highlight clades with informal group names. Fossil lineages are indicated with a dagger (†). Details of the fossil taxa are presented in Appendix 1.

    img-z16-1_03.jpg

    Neopterygii C. T. Regan 1923b:458
    [J. A. Moore and T. J. Near 2020]

  • Definition. Defined as a minimum-crown-clade by Moore and Near (2020c) as: “The least inclusive crown clade containing Lepisosteus osseus (Linnaeus 1758), Amia calva Linnaeus 1766, and Perca fluviatilis Linnaeus 1758.”

  • Etymology. From the ancient Greek νἐος (n̍iːo͡Ʊz), meaning new, and πτερὀν (t̍εɹαːn), meaning fin or wing.

  • Registration number. 210.

  • Reference phylogeny. Diogo (2007, figs. 3, 4) was designated as the primary reference phylogeny by Moore and Near (2020c). See Figures 2 and 3 for summary phylogenies of the major clades in Neopterygii. The placements of the pan-holosteans and Pan-Teleostei fossil taxa in the phylogeny are on the basis of inferences from analyses of morphological characters (Patterson 1977; Patterson and Rosen 1977; Arratia 1991, 1997, 1999, 2000a, 2001, 2008, 2013, 2016, 2017; Arratia and Thies 2001; Arratia and Tischlinger 2010; Taverne 2013; Sferco et al. 2015; Giles et al. 2017, 2023; Latimer and Giles 2018; Bean and Arratia 2020; Veysey et al. 2020; Arratia et al. 2021; Bean 2021; C. Shen and Arratia 2021).

  • Phylogenetics. The earliest phylogenetic investigations of Neopterygii resulted in tree topologies that depicted Holostei (Lepisosteidae and Amia) plus Teleostei as a monophyletic group (e.g., G. J. Nelson 1969a; Patterson 1973; Wiley 1976; Lauder and Liem 1983; Wiley and Schultze 1984; Maisey 1986). Phylogenetic analyses of morphological data matrices resolve Neopterygii as monophyletic (Olsen 1984; Olsen and McCune 1991; Gardiner et al. 1996; Coates 1999; Cavin and Suteethorn 2006; Hurley et al. 2007; Arratia and Tischlinger 2010; L. Grande 2010; Xu and Gao 2011; Xu and Wu 2012; Xu et al. 2012; Arratia 1999, 2013; Xu, Gao, et al. 2014; Poyato-Ariza 2015; Xu and Ma 2016; Xu and Zhao 2016; Giles et al. 2017, 2023; Argyriou et al. 2018, 2022; Latimer and Giles 2018; López-Arbarello and Sferco 2018; Ren and Xu 2021; Xu 2021; Mu et al. 2022; Yuan et al. 2022).

  • One of the earliest molecular phylogenetic studies of ray-finned fishes used DNA sequences of small fragments of three mtDNA protein coding genes and failed to resolve Neopterygii as monophyletic (Normark et al. 1991). Phylogenetic analysis of complete mtDNA genome sequences strongly resolves Neopterygii as paraphyletic, with Acipenseriformes and Holostei as sister lineages (Inoue et al. 2003a). Molecular phylogenetic analyses of Sanger-sequenced nuclear genes, combinations of nuclear and mtDNA genes, and phylogenomic studies all resolve Neopterygii as monophyletic (Kikugawa et al. 2004; Alfaro, Santini, et al. 2009; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; Broughton et al. 2013; M.-Y. Chen et al. 2015; Betancur-R et al. 2017; Hughes et al. 2018; Vialle et al. 2018; Wcisel et al. 2020).

  • Composition. Neopterygii includes more than 35,045 living species classified in Holostei and Teleostei (Near, Eytan, et al. 2012; Fricke et al. 2023). Fossil neopterygian lineages classified as Pan-Teleostei include †Ankylophoriformes, †Ascalabos, †Aspidorhynchidae, †Atacamichthys, †Catervariolus, †Dorsetichthys, †Ichthyodectiformes, †Ichthyokentema, †Leptolepis, †Pachycormidae, †Pholidophoridae, †Prohalecites, †Tharsis, and †Varasichthyidae (Patterson and Rosen 1977; J. Gaudant 1978; Arratia 1981; Arratia and Tischlinger 2010; Taverne 2011b, 2013; Arratia 2013; Arratia and Schultze 2024). Fossil lineages of pan-holostean neopterygians include †Dapediidae and †Hulettia (Schaeffer and Patterson 1984; Latimer and Giles 2018; López-Arbarello and Sferco 2018). Details of the ages and locations of the fossil taxa are presented in Appendix 1. Over the past 10 years 3,657 new living species of Neopterygii have been described (Fricke et al. 2023), comprising approximately 10.4% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Neopterygii include (1) number of fin-rays in the anal and dorsal fins equal in number to endoskeletal supports (Patterson 1973; Patterson and Rosen 1977; Lauder and Liem 1983), (2) premaxilla with interior process that lines front part of nasal pit (Patterson 1973; Patterson and Rosen 1977), (3) vomer attached to underside of ethmoid (Patterson 1973), (4) coronoid process on articular (Patterson 1973; Patterson and Rosen 1977), (5) vertically oriented suspensorium (Patterson 1973), (6) dorsal limb of preopercle narrow (Patterson 1973), (7) symplectic present and is an outgrowth of the hyomandibular cartilage (Patterson 1973; Patterson and Rosen 1977), (8) enhanced upper pharyngeal dentition (Patterson 1973; Patterson and Rosen 1977; Lauder and Liem 1983), (9) clavicle lost or reduced to small plate lateral to cleithrum (Patterson 1973; Wiley 1976; Patterson and Rosen 1977; Lauder and Liem 1983), (10) basipterygoid process entirely composed of parasphenoid (Wiley 1976), (11) posterior commissure between the supraorbital and infraorbital canals (Wiley 1976), (12) uncinate process on first and second infrapharyngobranchials (Wiley 1976), (13) infrabranchials laterally supported (Wiley 1976), (14) differentiated dorsal gill arch musculature (Wiley 1976), (15) four basibranchial copulae (Wiley 1976), (16) quadratojugal braces the quadrate (Gardiner 1984), (17) antorbitals present (Gardiner 1984), (18) palatoquadrate disconnected from dermal cheek bones dorsally and posteriorly (Gardiner 1984), (19) hyoid facet directed posteroventrally (Gardiner and Schaeffer 1989; Coates 1999), (20) maxilla elongate and shallow (L. Grande and Bemis 1998; Hurley et al. 2007; López-Arbarello and Sferco 2018), (21) maxilla detached from preopercle (Gardiner and Schaeffer 1989; Xu, Gao, et al. 2014; López-Arbarello and Sferco 2018), (22) upper-most hypaxial caudal rays with a bundle of elongate fin ray bases that extend over several hypurals (Gardiner et al. 1996; Hurley et al. 2007), (23) ventral cranial-otic fissure closed by bone (Coates 1999), (24) canal for dorsal aorta secondarily absent (Coates 1999), (25) cerebellar corpus arches above fourth ventricle (Coates 1999), (26) presence of one or more accessory postcleithra (Arratia 1999; Hurley et al. 2007), (27) rostral-postrostral and frontal contact wholly or partially separating nasal bones (Xu, Gao, et al. 2014), (28) nasal process on premaxilla (Xu, Gao, et al. 2014), (29) four or more infraorbitals between antorbital and dermosphenotic (Xu, Gao, et al. 2014), (30) presence of mobile maxilla in cheek (Xu, Gao, et al. 2014), (31) interopercle present (Xu, Gao, et al. 2014; López-Arbarello and Sferco 2018), (32) presence of medial gular bones (Xu, Gao, et al. 2014), (33) presence of peg-like anterior process of maxilla (Xu, Gao, et al. 2014), (34) infraorbitals and suborbitals broadly overlap preopercle (Giles et al. 2017), (35) postrostral bone absent (López-Arbarello and Sferco 2018), (36) supramaxilla present (López-Arbarello and Sferco 2018), (37) subopercle with ascending process (López-Arbarello and Sferco 2018), (38) absence of a distinguishable spiracularis of the constrictor mandibularis (Datovo and Rizzato 2018), (39) posterior end of maxilla ends behind orbit (Xu 2021), and (40) posttemporals broad, nearly as wide as extrascapular (Xu 2021).

  • Synonyms. Cope's (1877b:293–294) revised definition of Actinopteri, Regan's (1904b:331–332, 1909b:76–82) delimitation of Teleostei, and Goodrich's (1930:xvii) composition of Holostei were limited to Amia calva, Lepisosteidae, and Teleostei and are all approximate synonyms of Neopterygii (Moore and Near 2020c). While not a formal taxonomic name, the term “crown Neopterygii” is an ambiguous synonym of Neopterygii.

  • Comments. In a study of the morphology of Lepisosteidae, Regan (1923b:458) justified the use of a new group name (italics added to clade names): “Holostei and Teleostei, therefore are one group, for which it seems better to use the name Neopterygii, rather than to use Holostei or Teleostei in a new and extended sense.” Among the earliest studies of actinopterygian relationships after the introduction of phylogenetic systematics, Neopterygii is resolved as the clade containing Holostei and Teleostei (G. J. Nelson 1969a; Patterson 1973) and was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade. The oldest fossil taxon of Neopterygii is the pan-amiiform †Watsonulus eugnathoides from the Induan (251.9–249.9 Ma) in the Triassic of Madagascar (Olsen 1984; Giles et al. 2017, 2023). The crown age of Neopterygii estimated from Bayesian relaxed molecular clock analyses ranges from the Permian to the Carboniferous between 278 and 318 million years ago (Giles et al. 2017).

  • img-z19-3_03.gif

    Holostei J. Müller 1845a:420
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Amia calva Linnaeus 1766 and Lepisosteus osseus (Linnaeus 1758), but not Perca fluviatilis Linnaeus 1758. This is a minimum-crown-clade definition with an external specifier.

  • Etymology. From the ancient Greek ὃλoς (h̍o͡Ʊlo͡Ʊz), meaning whole, entire, or complete, and ὀστέoν (̍αːstIәn), meaning bone.

  • Registration number. 881.

  • Reference phylogeny. A phylogeny inferred from concatenated DNA sequences of 1,105 exons (Hughes et al. 2018, fig. S2). See Figures 2 and 3 for the relationship of Holostei among the major lineages of Actinopterygii. Phylogenetic relationships among the lineages of Holostei are shown in Figure 5B. Placements of the fossil holostean taxa in the phylogeny are on the basis of inferences from morphological analyses (Olsen 1984; Schultze and Wiley 1984; Lambers 1995; Gardiner et al. 1996; Wenz 1999; Xu and Gao 2011; López-Arbarello 2012; Xu and Wu 2012; Xu et al. 2012, 2018; Cavin et al. 2013; López-Arbarello et al. 2014, 2019, 2020; Xu. Zhao, et al. 2014; Poyato-Ariza 2015; Xu and Shen 2015; Brito et al. 2017; Sun et al. 2017; Ebert 2018; Latimer and Giles 2018; López-Arbarello and Sferco 2018; Ren and Xu 2021; Brownstein 2022; Brownstein and Lyson 2022; Brownstein et al. 2023).

  • Phylogenetics. The monophyly of Holostei was supported in one of the earliest phylogenetic systematic perspectives on the relationships of vertebrates (G. J. Nelson 1969a), reflecting pre-cladistic hypotheses that grouped Amia and Lepisosteidae (Regan 1923b; Goodrich 1930). An assessment of skeletal morphology led to the conclusion that Holostei is paraphyletic, with Amia calva as the sister lineage of Teleostei (Patterson 1973). Nearly every molecular phylogenetic analysis from the earliest efforts using partial-gene DNA sequences to phylogenomic analyses resolves Holostei as monophyletic (Normark et al. 1991; Inoue et al. 2003a; Broughton 2010; Near, Eytan, et al. 2012; Faircloth et al. 2013; Braasch et al. 2016; Hughes et al. 2018; Mu et al. 2022). In addition, a phylogenetic analysis of 70 morphological character state changes resolved Holostei as monophyletic (Hurley et al. 2007). A critical examination of morphology in bowfin, gars, teleosts, and several fossil lineages demonstrated that nearly all of the proposed characters supporting the hypothesis that Amia and teleosts share common ancestry are also present in gars (L. Grande 2010). Subsequent morphological phylogenetic analyses consistently resolve Holostei as monophyletic (Hurley et al. 2007; L. Grande 2010; Xu and Gao 2011; Xu and Wu 2012; Xu et al. 2012; Cavin et al. 2013; Xu, Gao, et al. 2014; Xu, Zhao, et al. 2014; Poyato-Ariza 2015; Xu and Shen 2015; Xu and Ma 2016; Xu and Zhao 2016; Giles et al. 2017, 2023; Sun et al. 2017; Argyriou et al. 2018, 2022; Latimer and Giles 2018; López-Arbarello and Sferco 2018; Xu et al. 2018, 2019; López-Arbarello et al. 2020; Ren and Xu 2021; Xu 2021; Yuan et al. 2022; Feng et al. 2023). As such, Holostei exemplifies one of the first conflicts in ichthyological systematics between morphological and molecular phylogenetic analyses (Patterson 1994:65–70) that was reconciled through continued morphological and genomic phylogenetic studies, in this case offering overwhelming support for the monophyly of Holostei (e.g., Hurley et al. 2007; L. Grande 2010; Near, Eytan, et al. 2012; Hughes et al. 2018; López-Arbarello and Sferco 2018; A. W. Thompson et al. 2021).

  • Composition. There are nine living species of Holostei, two species of Amia, and seven species of Lepisosteidae (Suttkus 1963; L. Grande 2010; Brownstein et al. 2022). There are several extinct pan-amiiform taxa that include †Amiopsis, †Caturus, †Cyclurus, †Ionoscopus, †Panxianichthys, †Sinamia, †Solnhofenamia, †Vidalamia, and †Watsonulus. Extinct pan-lepisosteiform lineages include †Araripelepidotes, †Cuneatus, †Fuyuanichthys, †Lepidotes, †Macrosemius, †Masillosteus, †Nhanulepisosteus, †Obaichthyidae, †Pliodetes, †Semionotus, †Thaiichthys, and †Ticinolepis (L. Grande and Bemis 1998; Wenz 1999; L. Grande 2010; López-Arbarello 2012; Xu and Wu 2012; Cavin et al. 2013; Xu, Zhao, et al. 2014; Xu and Shen 2015; López-Arbarello et al. 2016; Brito et al. 2017). Details of the ages and locations of fossil holosteans are presented in Appendix 1. Over the past 10 years no new living species of Holostei have been described (Fricke et al. 2023), but one species was elevated from synonymy with Amia calva (Brownstein et al. 2022).

  • Diagnostic apomorphies. Morphological apomorphies for Holostei include (1) posterior extent of median rostral bone in adults reduced (L. Grande 2010), (2) anterior arm on antorbital with a tube-like canal (L. Grande 2010; Xu et al. 2018), (3) adults with two vertebral centra fused into the occipital condyle (L. Grande 2010), (4) pterotic bone absent (L. Grande 2010), (5) adults with paired vomer (L. Grande 2010), (6) coronoid process of mandibula involves more than one bone (L. Grande 2010), (7) supraangular bone present (L. Grande 2010), (8) caudal region with both paired and median neural spines (L. Grande 2010), (9) normally all primary rays in caudal fin branched (L. Grande 2010), (10) fringing fulcra present on upper and lower margins of caudal fin (L. Grande 2010), (11) presence of anterior and posterior clavicle elements (L. Grande 2010), (12) four hypobranchials present (L. Grande 2010), (13) long nasal process that is tightly sutured to the frontals attaches immovable premaxilla to braincase (L. Grande 2010; Xu et al. 2018), (14) anterior portion of premaxilla pierced by olfactory foramen and lies in nasal pit (L. Grande 2010), (15) sphenotic with dermal component (L. Grande 2010; Xu et al. 2018), and (16) presence of a larval attachment organ that is a compound super-organ located at the front of the snout (Pinion et al. 2023).

  • Synonyms. There are no synonyms of Holostei.

  • Comments. Müller (1845a) delimited Holostei as including Polypteridae and Lepisosteidae. Later definitions of Holostei limited the group to Amia calva, pan-amiiforms, pan-lepisosteiforms, and Lepisosteidae (Regan 1923b; Goodrich 1930; L. Grande 2010). The alternative phylogenetic hypothesis that A. calva and Teleostei are sister lineages to the exclusion of Lepisosteidae was introduced by Patterson (1973). If future phylogenetic analyses find support for this hypothesis, the use of an external specifier in the clade definition would render Holostei inapplicable and Halecostomi would be an appropriate name for the smallest clade containing A. calva and Teleostei, but not Lepisosteidae. We were motivated to include an external specifier because the situation with Holostei and Halecostomi was used as an example in the Phylonyms volume of how to create a definition that will make a name inapplicable in the context of some phylogenies (de Queiroz et al. 2020a:xxvii). The earliest holostean is the pan-amiiform †Watsonulus eugnathoides from the Induan (251.9–249.9 Ma) in the Triassic of Madagascar (Olsen 1984; Giles et al. 2017, 2023). Fossil-calibrated Bayesian relaxed molecular clock analyses place the crown age of Holostei between 248 and 312 million years ago (Near, Eytan, et al. 2012, tbl. S1), which spans the Lower Triassic, Permian, and Upper Pennsylvanian (Carboniferous).

  • img-z21-2_03.gif

    Teleostei J. Müller 1845b:129
    [J. A. Moore and T. J. Near 2020]

  • Definition. Defined as a minimum-crown-clade by Moore and Near (2020f) as: “The least inclusive crown clade that contains Hiodon tergisus Lesueur 1818 (Osteoglossomorpha), Elops saurus Linnaeus 1766 (Elopomorpha), Engraulis encrasicolus (Linnaeus 1758) (Otocephala/ Clupeomorpha), and Perca fluviatilis Linnaeus 1758 (Euteleostei).”

  • Etymology. From the ancient Greek τέλειoς (t̍εlƗᵻo͡Ʊz), meaning perfect or complete, and ὀστέoν (̍αːstIәn), meaning bone.

  • Registration number. 212.

  • Reference phylogeny. Diogo (2007, figs. 3, 4) was designated as the primary reference phylogeny by Moore and Near (2020f). See Figures 2 and 3 for summary phylogenies of major clades that comprise Teleostei. The phylogenetic placement of the fossil taxon †Tselfatiiformes in Figure 3 is on the basis of analysis of morphological characters (Cavin 2001).

  • Phylogenetics. The first phylogenetic analyses supporting the monophyly of Teleostei were inferred from a distribution of derived character states without an analysis of a coded character data matrix using an explicit optimality criterion (Patterson 1977; Patterson and Rosen 1977). Subsequent phylogenetic analyses of morphological characters consistently resulted in teleost monophyly (Arratia 1991, 1997, 1999, 2001, 2008, 2013, 2017; Diogo 2007; Gouiric-Cavalli and Arratia 2022). Many of these morphological studies did not include a broad sampling of teleost diversity as they were aimed at resolving relationships among Teleostei and stem lineages that comprise the more inclusive Pan-Teleostei (Moore and Near 2020e).

  • The earliest molecular phylogenetic studies of ray-finned fishes used DNA sequences from small fragments of mtDNA and nuclear ribosomal RNA genes and did not resolve teleosts as monophyletic or did so with low node support (Normark et al. 1991; Lê et al. 1993). Starting in the early 21st century, molecular phylogenetic analyses ranging from the use of whole mtDNA genomes to phylogenomic analyses consistently resolve Teleostei as monophyletic (Inoue et al. 2003a; Hurley et al. 2007; Alfaro, Santini, et al. 2009; Broughton 2010; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; Austin et al. 2015; M.-Y. Chen et al. 2015; Bian et al. 2016; Betancur-R et al. 2017; Hughes et al. 2018; Vialle et al. 2018; Roth et al. 2020; Wcisel et al. 2020; Mu et al. 2022; Parey et al. 2023).

  • Composition. Teleostei contains more than 35,035 living species (Fricke et al. 2023) classified in Oseanacephala and Clupeocephala. Fossil teleosts include the †Tselfatiiformes (Cavin 2001). Details of the age and location of the fossil tselfatiiform taxon are presented in Appendix 1. Over the past 10 years 3,657 new living species of Teleostei have been described (Fricke et al. 2023), composing 10.4% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Teleostei include (1) presence of endoskeletal basihyal (G. J. Nelson 1969a; Patterson 1977; Arratia 1999, 2000c, 2008), (2) absence of a structure on ventral surface of basioccipital for cranial attachment of aortic ligament (Patterson 1975; Patterson and Rosen 1977; De Pinna 1996), (3) three hypobranchials (Patterson 1977), (4) four pharyngobranchials (Patterson 1977; De Pinna 1996), (5) seven hypurals in caudal skeleton (Patterson 1977; Patterson and Rosen 1977; De Pinna 1996), (6) base of fin rays on upper lobe of caudal fin attaches to or overlies no more than one hypural (Patterson and Rosen 1977; Arratia 1996b, 1997), (7) craniotemporal muscle present (Stiassny 1986; De Pinna 1996; Arratia 1999, 2000c; Wiley and Johnson 2010), (8) hypurals 1 and 2 laterally fused in adults (Arratia 1991), (9) absence of dorsal processes of the bases of the innermost primary caudal rays of upper lobe (Arratia 1991, 1996b, 2000c, 2008), (10) lateral forebrain bundle composed of myelinated fibers (De Pinna 1996; Wiley and Johnson 2010), (11) presence of accessory nasal sacs (X. Y. Chen and Arratia 1994; De Pinna 1996; Arratia 1999, 2000c, 2008; Wiley and Johnson 2010), (12) hyoidean artery pierces either both hypohyals or ventral hypohyal (Arratia 1999, 2000c, 2008), (13) pharyngobranchials with three ossified elements and a tooth plate-bearing cartilaginous element (Arratia 1999, 2000c, 2008; Wiley and Johnson 2010), (14) five or fewer ural neural arches modified as uroneurals (Arratia 1999, 2008; Wiley and Johnson 2010), (15) absence of notch in deep dorsal ascending margin of dentary (Arratia 2008, 2013, 2017), (16) many developed epipleural intermuscular bones in abdominal and caudal region (Arratia 2008), (17) parahypural haemal arch in adults not fused laterally to autocentrum (Arratia 2008), (18) uroneural 1 reaches anterior to preural centrum 2 (Wiley and Johnson 2010), (19) presence of an independent endoskeletal basihyal (Wiley and Johnson 2010), (20) absence of segmentum buccalis of adductor mandibulae (Datovo and Rizzato 2018), (21) presence of dilatator process on opercle (Datovo and Rizzato 2018), (22) presence of adductor crest (Datovo and Rizzato 2018), and (23) autocentrum of vertebrae with thickened lateral wall and series of ornaments including crests, grooves, and pits (Arratia 1997, 1999, 2013; Peskin et al. 2020).

  • Synonyms. Teleocephala (de Pinna 1996:159; Wiley and Johnson 2010:129–130; J. S. Nelson et al. 2016:132–133) is an ambiguous synonym of Teleostei. Many authors (Patterson 1977; Patterson and Rosen 1977; de Pinna 1996; Arratia 2001, 2013; Hilton 2022) use Teleostei as the name for a more inclusive clade that includes several stem fossil lineages (e.g., †Ichthyodectiformes, †Leptolepis, †Pholidophorus, and †Varasichthyidae), which is synonymous with Pan-Teleostei (Moore and Near 2020e).

  • Comments. Müller (1845b) introduced, named, and diagnosed Teleostei with a composition that is nearly identical to the delimitation presented here. Teleosts are an iconic lineage of vertebrates, but evidence for their monophyly, identification of major lineages of teleosts, and resolution of teleost phylogeny did not come into focus until the second half of the 20th century (Gosline 1965; Greenwood et al. 1966; G. J. Nelson 1969a, 1969c; Patterson 1977). The results of this research inaugurated a dramatic shift in ichthyology regarding Teleostei, a situation described by Patterson (1997:201) as: “An analogy is to imagine the situation in mammalogy if monotremes, marsupials, and placentals were not distinguished until 1966.”

  • Bayesian relaxed molecular clock analyses of Teleostei result in an average posterior crown age estimate of 239.6 million years ago, with the credible interval ranging between 224.5 and 256.5 million years ago (Giles et al. 2017).

  • img-z22-5_03.gif

    Oseanacephala C. E. Thacker and T. J. Near, new clade name

  • Definition. The least inclusive crown clade that contains Anguilla rostrata (Lesueur 1817) and Osteoglossum bicirrhosum (Cuvier 1829), but not Engraulis encrasicolus (Linnaeus 1758) or Perca fluviatilis Linnaeus 1758. This is a minimum-crown-clade definition with external specifiers.

  • Etymology. Oseanacephala is a partial acronym composed of the first two letters of Osteoglossomorpha and the first letter from the remaining lineages that comprise the clade: Elopiformes, Albulidae, Notacanthiformes, and Anguilliformes. The suffix is from the ancient Greek ϰεϕαλή (kεf̍αːlә), meaning the head of a human or other animal.

  • Registration number. 882.

  • Reference phylogeny. A phylogeny inferred from concatenated DNA sequences of 1,105 exons (Hughes et al. 2018, fig. S2). See Figures 2 and 3 for the resolution of living lineages of Oseanacephala in the phylogeny of Actinopterygii. See Figure 6 for the phylogenetic relationships of living and fossil lineages of Oseanacephala. Phylogenetic placements of the pan-osteoglossomorphs †Jiuquanichthys and †Lycoptera are on the basis of inferences from morphological analyses (G.-Q. Li and Wilson 1996, 1999; J.-Y. Zhang 1998, 2006; Hilton 2003; Murray et al. 2018).

  • Phylogenetics. In contrast to the substantial support for teleost monophyly from morphological and molecular phylogenetic analyses, uncertainty has remained regarding the relationships among the teleost lineages Clupeocephala, Elopomorpha, and Osteoglossomorpha (Hilton and Lavoué 2018; Dornburg and Near 2021; Takezaki 2021). Taeniopaedia was introduced as a name for the group that included Elopomorpha and Clupeomorpha (Greenwood et al. 1967), which was presented as “Division I” in the classification of teleosts (Greenwood et al. 1966). The morphological phylogeny presented in Patterson and Rosen (1977) resolved Clupeocephala and Elopomorpha as a clade supported with two traits: the presence of two uroneurals in the caudal skeleton that extend beyond ural centrum 2 and the presence of well-developed epipleural intermuscular bones. Arratia (1997) inferred a phylogeny of Pan-Teleostei using parsimony analyses of 131 character state changes coded from living and fossil taxa, resulting in a hypothesis where Elopomorpha is the sister lineage of all other teleosts.

  • Molecular phylogenetic analyses have resulted in all three possible relationships among Clupeocephala, Elopomorpha, and Osteoglossomorpha (Inoue et al. 2001; Hurley et al. 2007; Broughton 2010; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; Faircloth et al. 2013; J. N. Chen et al. 2014; Bian et al. 2016; Betancur-R et al. 2017). The earliest molecular phylogenetic studies of teleosts resolved Elopomorpha and Osteoglossomorpha as sister lineages (Lê et al. 1993), which is a frequent result in phylogenomic analyses (M.-Y. Chen et al. 2015; Bian et al. 2016; Lin et al. 2016; Hughes et al. 2018; Vialle et al. 2018; Hao et al. 2020; Roth et al. 2020; Wcisel et al. 2020; Takezaki 2021; Parey et al. 2023). Evidence from genomic organization in the form of the conservation of gene adjacency and the proportion of shared chromosomal breakpoints support monophyly of Oseanacephala (Parey et al. 2023).

  • Composition. There are currently 1,361 living species of Oseanacephala (Fricke et al. 2023) classified in Elopomorpha and Osteoglossomorpha. Fossil lineages of Oseanacephala include the pan-osteoglossomorphs †Jiuquanichthys and †Lycoptera. Details of the ages and locations of the fossil taxa are presented in Appendix 1. Over the past 10 years 139 new living species of Oseanacephala have been described, comprising 10.2% of the living species diversity in the clade.

  • Diagnostic apomorphies. All lineages of Oseanacephala share a chromosomal rearrangement, where duplicated chromosomes 1a and 2a are fused and lineages of Clupeocephala are characterized by an independent fusion of duplicated chromosomes 1b and 2b (Parey et al. 2023). There are no known morphological apomorphies for Oseanacephala; however, fusion of the retroarticular with the angular or the articular is shared by Elopomorpha, Hiodon, and Mormyridae (Parey et al. 2023). The absence of this trait in Gymnarchus niloticus, Notopteridae, Osteoglossidae, and Pantodon may represent a secondary loss in these lineages of Osteoglossomorpha (Parey et al. 2023).

  • Synonyms. Eloposteoglossocephala (Parey et al. 2023) is an ambiguous synonym of Oseanacephala.

  • Comments. The resolution of Oseanacephala is completely driven by molecular phylogenetic analyses and consideration of genomic organization. From the start of phylogenetic investigations of teleosts using morphology, the hypothesis that Elopomorpha and Osteoglossomorpha are sister lineages was never proposed (Patterson and Rosen 1977; Arratia 1997, 1999, 2000c). It is not clear what insight on the evolutionary diversification of teleosts is gained through the resolution of the relationships among Clupeocephala, Elopomorpha, and Osteoglossomorpha, but at minimum it may motivate a reexamination of jaw anatomy and bite kinematics between the bony-tongued Osteoglossomorpha and the complex pharyngeal jaw morphology in Anguilliformes. This resolution also invites investigation of potential commonalities between the robust larvae and juveniles of osteoglossomorph species and the leptocephalus larvae characteristic of Elopomorpha.

  • The earliest Oseanacephala fossil is the pan-elopiform †Anaethalion zapporum from the Kimmeridgian (154.8–149.2 Ma) in the Jurassic of Germany (Arratia 2000c). A Bayesian relaxed molecular clock analysis of Oseanacephala resulted in an average posterior crown age estimate of 223.98 million years ago, but no credible interval was reported (Vialle et al. 2018).

  • img-z25-3_03.gif

    FIGURE 6.

    Phylogenetic relationships of the major living lineages and fossil taxa of Oseanacephala, Osteoglossomorpha, Osteoglossiformes, Osteoglossidae, Elopomorpha, Elopiformes, Albulidae, Notacanthiformes, Anguilliformes, Synaphobranchoidei, Anguilloidei, Muraenoidei, and Congroidei. Asterisk identifies lineages currently classified as Congridae. Lineages currently classified as Congridae are highlighted with an asterisk. Filled circles identify the common ancestor of clades, with formal names defined in the clade accounts. Open circles highlight clades with informal group names. Fossil lineages are indicated with a dagger (†). Details of the fossil taxa are presented in Appendix 1.

    img-z24-1_03.jpg

    Elopomorpha P. H. Greenwood, D. E. Rosen,
    S. H. Weitzman, and G. S. Meyers 1966:350, 354–358, 393–394
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Elops saurus Linnaeus 1766, Albula vulpes (Linnaeus 1758), and Anguilla rostrata (Lesueur 1817). This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek ϰλλoΨ (Ɨl̍αːps), an epithet for fish that may mean either scaly or dumb, for example, “dumb as a fish” (D. W. Thompson 1947:62; Liddell et al. 1968:537) and µoρϕή (m̍ͻ͡ɹ fiː), meaning form or shape.

  • Registration number. 883.

  • Reference phylogeny. A phylogeny inferred from a concatenated dataset of DNA sequences of mitochondrial and nuclear genes and morphological characters (Dornburg et al. 2015, fig. 3). Phylogenetic relationships among living and fossil lineages of Elopomorpha are shown in Figure 6. The resolutions of fossil taxa in the phylogeny are on the basis of inferences from morphological characters (Arratia 1991, 1997, 1999, 2000b, 2000c, 2008, 2010b; Forey et al. 1996; Belouze 2002; Gallo and de Figueiredo 2002; Arratia and Tischlinger 2010; Forey and Maisey 2010; Mayrinck et al. 2010; de Figueiredo, Gallo, and Leal 2012; Pfaff et al. 2016; Guinot and Cavin 2018; Alves et al. 2020; Bean and Arratia 2020; Bean 2021; Hernández-Guerrero et al. 2021).

  • Phylogenetics. The shared presence of specialized leptocephalus larvae was the primary character that led to the delimitation of Elopomorpha to include Elopiformes (including Albulidae), Notacanthiformes, and Anguilliformes (Greenwood et al. 1966). The monophyly of Elopomorpha was challenged in several morphological and molecular inferences that included a de-emphasis on the importance of the leptocephalus larvae (Gosline 1971:100; Nybelin 1971; Hulet and Robins 1989; Filleul and Lavoué 2001; Obermiller and Pfeiler 2003); however, surveys of osteological traits, explicit phylogenetic analyses of morphological character state changes, and molecular phylogenetic analyses consistently resolve elopomorphs as monophyletic (Forey 1973a; G. J. Nelson 1973; Greenwood 1977; Patterson and Rosen 1977; Forey et al. 1996; Inoue et al. 2004; Forey and Maisey 2010; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; J. N. Chen et al. 2014).

  • While analyses of morphological and molecular characters consistently resolve Elopomorpha as monophyletic, relationships among the elopomorph subclades vary among phylogenetic studies. Albulidae, containing Albula, Pterothrissus, and the recently described Nemoossis (Hidaka et al. 2017), is resolved as paraphyletic in some morphological and molecular studies (Forey 1973b; Inoue et al. 2004; Dornburg et al. 2015), but is monophyletic in others (Forey et al. 1996; de Figueiredo, Gallo, and Leal 2012; Alves et al. 2020). Notacanthiformes is resolved as either sharing common ancestry with Albulidae (G. J. Nelson 1973; Greenwood 1977; Patterson and Rosen 1977; C. R. Robins 1989; Inoue et al. 2004; G. D. Johnson et al. 2012) or Anguilliformes (Forey 1973a; Forey et al. 1996; J. N. Chen et al. 2014; Dornburg et al. 2015). There are several morphological character state changes that support Albulidae as the sister lineage of a clade containing Notacanthiformes and Anguilliformes (Forey et al. 1996; Datovo and Vari 2014).

  • Composition. Elopomorpha currently contains 1,107 living species (Fricke et al. 2023) classified in Albulidae, Anguilliformes, Elopiformes, and Notacanthiformes. Fossil taxa of Elopomorpha include the pan-elopiforms †Anaethalion, †Daitingichthys, and †Paraelops (Arratia 1987a; Fielitz and Bardack 1992; de Figueiredo, Gallo, and Leal 2012); the pan-albulids †Baugeichthys, †Brannerion, †Bullichthys, †Farinichthys, †Lebonichthys, and †Osmeroides (Forey et al. 1996, 2003; Filleul 2000; Gallo and de Figueiredo 2002; Forey and Maisey 2010; Mayrinck et al. 2010); and the pan-anguilliforms †Abisaadia, †Anguillavus, †Enchelurus, †Hayenchelys, †Luenchelys, and †Urenchelys (Belouze 2002; Belouze et al. 2003; Pfaff et al. 2016; Guinot and Cavin 2018). Details of the ages and locations of the fossil taxa are presented in Appendix 1. Over the past 10 years 124 new living species of Elopomorpha have been described (Fricke et al. 2023), comprising 11.2% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Elopomorpha include (1) presence of the leptocephalus larval stage (Greenwood et al. 1966; Forey 1973a, 1973b; Forey et al. 1996; Inoue et al. 2004; Wiley and Johnson 2010), (2) fusion between angular and retroarticular bones of lower jaw (G. J. Nelson 1973), (3) presence of prenasal ossicles (Forey 1973a, 1973b; Forey et al. 1996; Wiley and Johnson 2010), (4) presence of pectoral splint (Forey 1973a, 1973b; Forey et al. 1996), (5) sternohyoides originates primarily on cleithrum (Greenwood 1977; Wiley and Johnson 2010), (6) spermatozoa flagellum with 9+0 axoneme arrangement and proximal centriole divided into two elongate bundles of four- and five-triplet structure (Matthei and Matthei 1975; Jamieson 1991; Wiley and Johnson 2010), (7) compound neural arch forms in a mass of cartilage over first preural and first ural centrum (Schultze and Arratia 1988; Arratia 1996a, 1997; Forey and Maisey 2010; Wiley and Johnson 2010), and (8) presence of a branchial spiracle (Forey and Maisey 2010).

  • Synonyms. Elopoidei (Gosline 1960:357) and Elopocephalai (Arratia 1999; Betancur-R, Broughton, et al. 2013; Betancur-R et al. 2017:13) are ambiguous synonyms of Elopomorpha.

  • Comments. Greenwood et al. (1966) introduced Elopomorpha as the name for a group that includes Albulidae, Anguilliformes, Elopiformes, and Notacanthiformes, and it is recognized in all subsequent classifications of Teleostei (e.g., G. J. Nelson 1969a; Patterson and Rosen 1977; Wiley and Johnson 2010; Betancur-R et al. 2017). Elopomorpha is an ancient lineage with the pan-elopid †Elopsomolos frickhingeri and pan-elopomorph †Anaethalion zapporum as the earliest known fossil taxa, both of which date from the Kimmeridgian (154.8–149.2 Ma) in the Jurassic (Arratia 2000c; Guinot and Cavin 2018). Bayesian relaxed molecular clock estimates of the crown age of Elopomorpha range between 157 and 200 million years ago in the Jurassic (Dornburg et al. 2015).

  • img-z26-7_03.gif

    Elopiformes P. H. Greenwood, D. E. Rosen,
    S. H. Weitzman, and G. S. Meyers 1966:354, 393
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Elops saurus Linnaeus 1766 and Megalops cyprinoides (Broussonet 1782), but not Albula vulpes (Linnaeus 1758). This is a minimum-crown-clade definition with an external specifier.

  • Etymology. From the ancient Greek ἔλλoΨ (Ɨl'αːps), an epithet for fish that may mean either scaly or dumb, for example, “dumb as a fish” (D. W. Thompson 1947:62; Liddell et al. 1968:537). The suffix is from the Latin word forma, meaning form, figure, or appearance.

  • Registration number. 884.

  • Reference phylogeny. A phylogeny inferred from a concatenated dataset of DNA sequences of mitochondrial and nuclear genes and morphological characters (Dornburg et al. 2015, fig. 3). Phylogenetic relationships of Elopiformes are presented in Figure 6. The placements of the fossil taxa in the phylogeny are on the basis of inferences from morphological characters (Arratia 2000c; de Figueiredo, Gallo, and Leal 2012; Alves et al. 2020; Hernández-Guerrero et al. 2021).

  • Phylogenetics. Elopiformes is consistently resolved as monophyletic in morphological and molecular phylogenetic studies (Forey 1973b; Demartini and Donaldson 1996; Forey et al. 1996; Filleul and Lavoué 2001; Obermiller and Pfeiler 2003; C. Wang et al. 2003; Inoue et al. 2004; Forey and Maisey 2010; de Figueiredo, Gallo, and Leal 2012; G. D. Johnson et al. 2012; K. L. Tang and Fielitz 2013; J. N. Chen et al. 2014; Dornburg et al. 2015; Poulsen et al. 2018; Alves et al. 2020; de Sousa et al. 2021; Hernández-Guerrero et al. 2021). Analyses of mtDNA sequences indicate there are multiple undescribed species masquerading as Elops smithi(McBrideetal.2010;Willifordetal.2022).

  • Composition. There are currently nine living species of Elopiformes classified in Elops and Megalops (Fricke et al. 2023). Fossil lineages of Elopiformes include the pan-megalopid †Elopoides and the pan-elopids †Elopsomolos and †Ichthyemidion (Forey 1973b; Poyato-Ariza 1995; Arratia 2000c). Details of the ages and locations of the fossil taxa are given in Appendix 1. Over the past 10 years no new living species of Elopiformes have been described (McBride et al. 2010; Fricke et al. 2023).

  • Diagnostic apomorphies. Morphological apomorphies for Elopiformes include (1) medial position of posterior opening of mandibular sensory canal within lower jaw (Forey et al. 1996; Wiley and Johnson 2010), (2) presence of posteriorly expanded preopercle (Arratia 2000c), (3) presence of posteriorly expanded opercles and subopercles (Arratia 2000c), (4) presence of well-developed process on mesethmoid (Arratia 2000c), (5) presence of lateral rostral bone (Arratia 2000c), (6) presence of elongated antorbital placed anterior to infraorbital (Arratia 2000c), (7) posterior margins of infraorbitals 3 and 4 do not reach anterior margin of preopercle (Arratia 2000c), (8) anterior portion of ceratohyal not fenestrated (Arratia 2000c), (9) first ossified pleural rib occurring on the fourth or more posterior centrum (Forey and Maisey 2010), and (10) presence of constrictor mandibularis dorsalis, levator arcus palatinia, and pars temporalis (Datovo and Rizzato 2018).

  • Synonyms. Elopoidei (Greenwood et al. 1966:393) is an approximate synonym of Elopiformes.

  • Comments. Greenwood et al. (1966) applied the name Elopiformes to a lineage that included Albulidae, Elopidae, and Megalopidae, a grouping proposed by Gosline (1960) on the basis of morphology of the caudal skeleton. Subsequent phylogenetic studies consistently resolve a clade that accords with our delimitation of Elopiformes as the sister lineage to all other elopomorphs (Forey et al. 1996; Inoue et al. 2004). Elopiformes is an ancient lineage dating to the Jurassic and the pan-elopid †Elopsomolos frickhingeri from the Kimmeridgian (154.8–149.2 Ma) of Germany is the earliest known fossil taxon (Arratia 2000c; Dornburg et al. 2015; Guinot and Cavin 2018). Bayesian relaxed molecular clock crown age estimates for Elopiformes range between 82 and 175 million years ago (Near, Eytan, et al. 2012).

  • img-z27-10_03.gif

    Albulidae P. Bleeker 1849:6, 12
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Albula vulpes (Linnaeus 1758), Nemoossis belloci (Cadenat 1937), and Pterothrissus gissu Hilgendorf 1877. This is a minimum-crown-clade definition.

  • Etymology. Albulae is a Latin name for the Tiber River in Italy (Livy 1919:14–15).

  • Registration number. 885.

  • Reference phylogeny. A phylogeny resulting from a phylogenetic analysis of morphological character state changes (Forey and Maisey 2010, fig. 13). Nemoossis belloci (Longfin Bonefish) is not included in any phylogenetic analyses, but it is assumed it will resolve as the sister species of Pterothrissus gissu (Japanese Gissu) (Hidaka et al. 2017). Phylogenetic relationships of Albulidae (bonefishes) are shown in Figure 6. The placements of fossil taxa in the phylogeny are on the basis of inferences from morphological characters (Fielitz and Bardack 1992; Gallo and de Figueiredo 2002; de Figueiredo, Gallo, and Leal 2012; Guinot and Cavin 2018; Alves et al. 2020; Hernández-Guerrero et al. 2021; L-Recinos et al. 2023).

  • Phylogenetics. Classifications of Teleostei from the early to mid-20th century grouped Albula and Pterothrissus in either Albulidae, Albuloidae, or Albuloidei (Boulenger 1904b:547–549; Goodrich 1909:387–388; Berg 1940:420; Greenwood et al. 1966). Reflecting alternative classifications that grouped Albula and Pterothrissus in separate and unrelated family rank taxonomic groups (Jordan 1905:44, 46–48), it was proposed that Pterothrissus is the sister lineage of a clade containing Notacanthiformes and Anguilliformes on the basis of shared similarities of an elongate snout, subterminal mouth, reduced ossification of the braincase, and inwardly turned head of the maxilla (Forey 1973a). Subsequent morphological studies consistently resolve Albulidae as monophyletic (Greenwood 1977; Forey et al. 1996), and several morphological phylogenetic analyses incorporated fossil taxa that are either more closely related to Albula or to the Pterothrissus-Nemoossis clade (Forey and Maisey 2010; de Figueiredo, Gallo, and Leal 2012; Guinot and Cavin 2018; Alves et al. 2020; Hernández-Guerrero et al. 2021; L-Recinos et al. 2023). Molecular phylogenies differ in their support for the monophyly of Albulidae. Analyses of mitochondrial DNA and concatenated nuclear genes each result in paraphyly of Albulidae, with Pterothrissus resolved as the sister lineage of Notacanthiformes (Inoue et al. 2004; G. D. Johnson et al. 2012; Dornburg et al. 2015); however, other phylogenetic studies using mitochondrial DNA result in the resolution of a monophyletic Albulidae (C. Wang et al. 2003; K. L. Tang and Fielitz 2013; Poulsen et al. 2018).

  • Composition. Albulidae currently contains 13 living species classified in Albula, Nemoossis, and Pterothrissus (Hidaka et al. 2017; Fricke et al. 2023). Fossil taxa of Albulidae include †Deltaichthys, †Hajulia, †Istieus, †Macabi, and †Nunaneichthys (Forey and Maisey 2010; de Figueiredo, Gallo, and Leal 2012; Guinot and Cavin 2018; Alves et al. 2020; Hernández-Guerrero et al. 2021; L-Recinos et al. 2023). Details of the ages and locations of the fossil taxa are presented in Appendix 1. There were no new living species of Albulidae described over the past 10 years, but there remains at least one undescribed species of Albula (Pickett et al. 2020).

  • Diagnostic apomorphies. Morphological apomorphies for Albulidae include (1) presence of subepiotic fossa (Forey et al. 1996; Wiley and Johnson 2010), (2) ectopterygoid with dorsal process (Forey et al. 1996; Wiley and Johnson 2010), (3) presence of fenestration within hyomandibular and metapterygoid suture that allows levator arcus palatine to pass through and insert on medial surface of palate (Forey et al. 1996; Wiley and Johnson 2010), and (4) sternohyoideus originating mainly on cleithrum (Forey et al. 1996).

  • Synonyms. Albuloidae (Berg 1940:420), Albuloidei (Greenwood et al. 1966:393; Forey 1973a:94), and Albuliformes (Forey et al. 1996:184; J. S. Nelson et al. 2016; Betancur-R et al. 2017:14) are all ambiguous synonyms of Albulidae.

  • Comments. When Bleeker (1849) introduced the name Albulidae, there was only one taxon, Albula, classified in the group (Günther 1868:468). Shortly after the description of Pterothrissus (Hilgendorf 1877), several classifications of teleosts grouped Albula and Pterothrissus in Albulidae (Boulenger 1904b:547–549; Goodrich 1909:387–388). Albulidae was selected as the clade name over its synonyms because they are redundant group names relative to Albulidae in ranked taxonomies. Albulidae is a valid family-group name under the International Code of Zoological Nomenclature (Van der Laan et al. 2014:64).

  • The earliest fossil taxa in Albulidae is †Nunaneichthys mexicanus from the Albian-Cenomanian (100.5–93.9 Ma) in the Cretaceous from Mexico (Hernández-Guerrero et al. 2021). There are no molecular divergence time estimates for Albulidae.

  • img-z29-4_03.gif

    Notacanthiformes E. S. Goodrich 1909:416
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Notacanthus chemnitzii Bloch 1788 and Halosaurus ovenii J. Y. Johnson 1864. This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek νῶτoν (no͡Ʊtәn), meaning of the back, and ἇκανθα (æk'ænθә), meaning thorn or spine. The suffix is from the Latin forma, meaning form, figure, or appearance.

  • Registration number. 886

  • Reference phylogeny. A phylogeny resulting from analysis of a concatenated dataset of DNA sequences from mitochondrial and nuclear genes and morphological characters (Barros-García et al. 2018, fig. 1b). Phylogenetic relationships of Notacanthiformes are presented in Figure 6. The placement of the fossil lineage †Echidnocephalus in the phylogeny is based on inferences from morphological characters (Forey et al. 1996; Arratia 2010b; Guinot and Cavin 2018).

  • Phylogenetics. Classifications of teleost fishes from the early 20th century grouped Notacanthidae (deep-sea spiny eels) and Halosauridae (halosaurs) with the pan-aulopiform †Dercetidae and Fierasfer, which is a synonym of the ophiid Carapus (Boulenger 1904b; Goodrich 1909:416–419). Regan (1909b) removed †Dercetidae and Fierasfer and limited the group Heteromi to Notacanthidae and Halosauridae. Notacanthiformes, comprising Notacanthidae and Halosauridae, was identified as one of the major lineages of Elopomorpha (Greenwood et al. 1966) and subsequent phylogenetic analyses have supported notacanthiform monophyly (Forey et al. 1996; Inoue et al. 2004; J. N. Chen et al. 2014; Dornburg et al. 2015; Barros-García et al. 2018; Poulsen et al. 2018). There is less certainty on the relationships of Notacanthiformes among major lineages of Elopomorpha. Some phylogenetic analyses of morphological and molecular characters place Notacanthiformes as the sister lineage of Albulidae (Greenwood 1977; Patterson and Rosen 1977; C. R. Robins 1989; C. Wang et al. 2003; Inoue et al. 2004; G. D. Johnson et al. 2012; Near, Eytan, et al. 2012), but other studies resolve Notacanthiformes and Anguilliformes as sister lineages (Forey 1973a; Forey et al. 1996; Santini, Kong, et al. 2013; K. L. Tang and Fielitz 2013; J. N. Chen et al. 2014; Dornburg et al. 2015). Forey et al. (1996) identified 14 morphological synapomorphies for a clade containing Notacanthiformes and Anguilliformes; many of these traits are character losses in the context of their evolution within Elopomorpha (Wiley and Johnson 2010).

  • Composition. There are currently 28 living species of Notacanthiformes (Fricke et al. 2023) classified in Notacanthidae and Halosauridae. Fossil lineages of Notacanthiformes include the pan-halosaurid †Echidnocephalus (Forey et al. 1996; Arratia 2010b). Details of the age and location of †Echidnocephalus are presented in Appendix 1. Over the past 10 years one new species of Notacanthiformes has been described (Fricke et al. 2023).

  • Diagnostic apomorphies. Morphological apomorphies for Notacanthiformes include (1) complete separation of parmalaris from remaining muscles of adductor mandibulae (Greenwood 1977; Datovo and Vari 2014), (2) nodule between maxillary head and palatine (Greenwood 1977; Wiley and Johnson 2010), (3) presence of posteriorly directed spine on maxilla (Forey et al. 1996; Wiley and Johnson 2010), and (4) pelvic fins connected by membrane (Forey et al. 1996; Wiley and Johnson 2010).

  • Synonyms. Heteromi (T. N. Gill 1893:133; Regan 1909a:82–83) and Halosauri (Garstang 1931:258) are approximate synonyms of Notacanthiformes.

  • Comments. Greenwood et al. (1966) limited Notacanthiformes to Notacanthidae and Halosauridae. The name Notacanthiformes was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade.

  • The earliest notacanthiform fossil taxon is the pan-halosaurid †Echidnocephalus troscheli from the Campanian (83.2–72.2 Ma) in the Cretaceous of Germany (Forey et al. 1996; Arratia 2010b). Bayesian relaxed molecular clock age estimates of Notacanthiformes result in an average posterior crown age estimate between 70 and 125 million years ago (Dornburg et al. 2015).

  • img-z30-6_03.gif

    Anguilliformes E. S. Goodrich 1909:403
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Myroconger compressus Günther 1870, Gymnothorax formosus Bleeker 1864b, Protanguilla palau Johnson, Ida, and Sakaue in G. D. Johnson et al. 2012, Synaphobranchus kaupi J. Y. Johnson 1862, Conger oceanicus (Mitchill 1818a), and Anguilla anguilla (Linnaeus 1758). This is a minimum-crown-clade definition.

  • Etymology. From the Latin Anguilla, meaning eel, and forma, meaning form, figure, or appearance.

  • Registration number. 887.

  • Reference phylogeny. A phylogeny inferred from a concatenated dataset of DNA sequences from three nuclear genes and two mitochondrial protein coding genes (Santini, Kong, et al. 2013, fig. 2). Phylogenetic relationships of Anguilliformes are presented in Figure 6.

  • Phylogenetics. Species classified as Anguilliformes were initially grouped with unrelated eel-like species in Apodes of Linnaeus (1758:242). By the middle of the 19th century, a taxonomic group comprising the modern Anguilliformes was established (Bleeker 1864c). Greenwood et al. (1966) delimited two groups within Anguilliformes, Anguilloidei for the typical eels and Saccopharyngoidei containing the morphologically bizarre deep-sea lineages that included Saccopharynx (swallowers), Eurypharynx pelecanoides (Pelican Eel), and Monognathus (onejaw gulpers). The saccopharyngoids are so morphologically unique that it has been proposed they were a divergent lineage not closely related to any living osteichthyans (Tchernavin 1947). The saccopharyngoid traits include the absences of ventral fins, pelvic girdle, opercular bones, and branchiostegals (Böhlke 1966; Bertelsen et al. 1989). The saccopharyngoids were included with all other eels in Boulenger's (1904b:599–605) Apodes and in Goodrich's (1909:403–408) Anguilliformes. In a classification of teleosts, Regan (1909b) grouped anguilloids and saccopharyngoids in Apodes, but he later put Saccopharynx in T. N. Gill and Ryder's (1883) Lyomeri, established to accommodate the saccopharyngoid Eurypharynx pelecanoides (Regan 1912a, 1912e). On the basis of comparative morphology, C. R. Robins (1989) countered the classification of Anguilliformes presented in Greenwood et al. (1966) and vigorously promoted the hypothesis that anguilloids and saccopharyngoids are distantly related. The delimitation of the saccopharyngoids was later expanded to include the bobtail snipe eels Cyema atrum and Neocyema erythrosoma (Raju 1974; Castle 1977).

  • Subsequent to the delimitation of Elopomorpha (Greenwood et al. 1966), there is broad support for the monophyly of Anguilliformes in morphological and molecular phylogenetic studies (Forey 1973a; Forey et al. 1996; Inoue et al. 2003b, 2004, 2010; Obermiller and Pfeiler 2003; C. Wang et al. 2003; López et al. 2007; G. D. Johnson et al. 2012; Santini, Kong, et al. 2013; K. L. Tang and Fielitz 2013; J. N. Chen et al. 2014; Dornburg et al. 2015; Poulsen et al. 2018). The use of morphological characters to investigate phylogenetic relationships of Anguilliformes is challenged by difficulties in constructing inclusive data matrices due to limited knowledge on anguilliform anatomy and the reductive nature of eel skeletons (Forey et al. 1996). The situation is improving with detailed studies of gill arch musculature (Springer and Johnson 2015), the pharyngeal jaw apparatus (G. D. Johnson 2019), and the pectoral girdle (da Silva and Johnson 2018). A recent phylogenetic analysis of Congroidei using 42 coded characters from the pectoral girdle demonstrates the potential for explicit phylogenetic analysis of morphological traits in resolving relationships within Anguilliformes (da Silva et al. 2019).

  • Despite the historic challenges of using morphology to investigate anguilliform phylogeny, parsimony analysis of a data matrix of morphological character state changes resulted in the nesting of saccopharyngoids within the anguilloids (Forey et al. 1996). The paraphyly of anguilloids relative to saccopharyngoids is reflected in several molecular phylogenetic analyses (Inoue et al. 2003b, 2004, 2010; Santini, Kong, et al. 2013; J. N. Chen et al. 2014; Dornburg et al. 2015; Poulsen et al. 2018). The issue of the phylogenetic affinities of saccopharyngoids is effectively settled, as evidenced by a proposed set of taxonomic groupings in Anguilliformes that do not include Saccopharyngiformes or Saccopharyngoidei, classifying them with the anguilloid lineages Anguillidae (freshwater eels), Moringuidae (spaghetti eels), Nemichthyidae (snipe eels), and Serrivomeridae (sawtooth eels) (K. L. Tang and Fielitz 2013). Molecular phylogenetic analyses resolve Anguilliformes into four clades: Synaphobranchoidei, Muraenoidei, Congroidei, and Anguilloidei (K. L. Tang and Fielitz 2013). Several currently recognized taxa within Anguilliformes are non-monophyletic in molecular phylogenetic analyses, including Chlopsidae (false morays), Coloconger (shottail eels), Congridae (conger eels), Cyematidae (bobtail snipe eels), Derichthyidae (narrowneck eels), and Nettastomatidae (Santini, Kong, et al. 2013; K. L. Tang and Fielitz 2013; Poulsen et al. 2018; Lü et al. 2019; K. Zhang, Zhu, et al. 2021; Huang et al. 2023).

  • Composition. Anguilliformes currently contains 1,057 species (Fricke et al. 2023) classified in Anguilloidei, Chlopsidae, Congroidei, Muraenoidei, and Synaphobranchoidei (K. L. Tang and Fielitz 2013). Over the past 10 years 122 new living species of Anguilliformes have been described, comprising 11.5% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Anguilliformes include (1) symplectic fused with quadrate (Forey et al. 1996; Wiley and Johnson 2010), (2) absence of first pharyngobranchial, gill arches displaced posteriorly and free from the neurocranium (Forey et al. 1996; Wiley and Johnson 2010; Espíndola et al. 2023), (3) absence of pelvic girdle and pelvic fins (Forey et al. 1996; Wiley and Johnson 2010), (4) body scales absent or embedded with a basket-weave pattern (C. R. Robins 1989; Wiley and Johnson 2010; G. D. Johnson et al. 2012; Espíndola et al. 2023), (5) ceratohyal with elongated anterior end (C. R. Robins 1989; Wiley and Johnson 2010), (6) anterior branchiostegals curve behind and above opercle (C. R. Robins 1989; Wiley and Johnson 2010; G. D. Johnson et al. 2012; Espíndola et al. 2023), (7) endopterygoid absent (G. D. Johnson et al. 2012; Espíndola et al. 2023), (8) single hypohyal or hypohyal absent (G. D. Johnson et al. 2012; Espíndola et al. 2023), (9) dorsal and anal fins confluent with caudal fin (G. D. Johnson et al. 2012; Espíndola et al. 2023), (10) fewer than eight caudal fin rays in each lobe (G. D. Johnson et al. 2012; Espíndola et al. 2023), (11) posttemporal absent (G. D. Johnson et al. 2012; Espíndola et al. 2023), (12) epurals absent (G. D. Johnson et al. 2012; Espíndola et al. 2023), (13) absence of levator internus 3 (Springer and Johnson 2015; Espíndola et al. 2023), (14) presence of musculus pharyngobranchialis 2-epibranchialis 1 (Springer and Johnson 2015; Espíndola et al. 2023), (15) presence of a single pharyngoclavicularis (Springer and Johnson 2015; Espíndola et al. 2023), (16) presence of rectus ventralis 3 and 4 (Springer and Johnson 2015; Espíndola et al. 2023), (17) absence of rectus communis (Springer and Johnson 2015; Espíndola et al. 2023), (18) levator internus 2 insertion includes upper tooth plate 4 (Springer and Johnson 2015; Espíndola et al. 2023), (19) hypobranchial 3 either absent or entirely cartilaginous (Springer and Johnson 2015; Espíndola et al. 2023), (20) absence of accessory element at distal end of ceratobranchial 4 (Springer and Johnson 2015; Espíndola et al. 2023), (21) adductor mandibulae originates on parietal (Espíndola et al. 2023), and (22) adductor mandibulae lacks segmentum mandibularis (Espíndola et al. 2023).

  • Synonyms. Apodes (Kaup 1856:1; Boulenger 1904b:600–605; Regan 1912e:377–379; Jordan 1923:130; Trewavas 1932:655–656) and Muraeni (Bleeker 1864c:113) are approximate synonyms of Anguilliformes. Encheli is a partial synonym of Anguilliformes (Garstang 1931:257).

  • Comments. The composition of Anguilliformes in Goodrich (1909:370, 403–404) is very close to that delimited here and in Greenwood et al. (1966), the differences being the addition of lineages discovered after these important studies (e.g., Castle 1977; G. D. Johnson et al. 2012). The name Anguilliformes was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade.

  • While there are several fossil lineages of pan-anguilliforms from the Cretaceous, the earliest fossil Anguilliformes are from the Ypresian (56.0–48.1 Ma) in the Eocene of Italy (Bannikov 2014b; Carnevale et al. 2014; Pfaff et al. 2016). Relaxed molecular clock analyses estimate the crown age of Anguilliformes between 84 and 116 million years ago (Santini, Kong, et al. 2013).

  • img-z32-6_03.gif

    Synaphobranchoidei P. Bleeker 1864a:13
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Synaphobranchus kaupi J. Y. Johnson 1862, Simenchelys parasitica Gill in Bean and Goode 1879, and Protanguilla palau Johnson, Ida, and Sakaue in G. D. Johnson et al. 2012. This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek σύν (s̍In), meaning together; ἁϕἠ (ɐf̍ε), meaning a joint or a fastening; and βραγχίoν (bɹ̍æɡki͡әn), Latinized as branchium, meaning a fish gill.

  • Registration number. 888.

  • Reference phylogeny. A phylogeny inferred from a concatenated dataset of DNA sequences from three nuclear genes and two mitochondrial protein coding genes (Santini, Kong, et al. 2013, fig. 2). Phylogenetic relationships of Synaphobranchoidei are presented in Figure 6.

  • Phylogenetics. Molecular phylogenetic analyses consistently resolve Protanguilla palau (Cave Eel) and species of Synaphobranchidae (cutthroat eels) as a monophyletic group (Santini, Kong, et al. 2013; K. L. Tang and Fielitz 2013; Poulsen et al. 2018). Some investigators contend that morphological character state changes support Protanguilla as the sister lineage of all other Anguilliformes (G. D. Johnson et al. 2012; Espíndola et al. 2023), but this inference is on the basis of the distribution of several key morphological traits and not the result of an explicit phylogenetic analysis of coded character state changes.

  • Composition. Synaphobranchoidei currently contains 53 species (Fricke et al. 2023) classified in Synaphobranchidae and Protanguilla (K. L. Tang and Fielitz 2013). Over the past 10 years 15 new living species of Synaphobranchoidei have been described (Fricke et al. 2023), comprising 28.3% of the living species diversity in the clade.

  • Diagnostic apomorphies. The leptocephalus larvae of species of Synaphobranchidae are unique among all other lineages of Anguilliformes in possessing vertically or diagonally elongated eyes (C. H. Robins and Robins 1989). The morphology of the larvae of Protanguilla palau is not known.

  • Synonyms. There are no synonyms of Synaphobranchoidei.

  • Comments. Bleeker (1864a,13) applied Synaphobranchoidei as a ranked taxonomic family to classify Synaphobranchus kaupi. Given the resolution of Synaphobranchidae and Protanguilla as sister lineages in molecular phylogenies (Santini, Kong, et al. 2013; Poulsen et al. 2018), K. L. Tang and Fielitz (2013, tbl. II) revised the classification of Anguilliformes with a new delimitation of Synaphobranchoidei that is the basis of the definition presented here. Bayesian relaxed molecular clock analysis estimates the crown age of Synaphobranchoidei between 55 and 108 million years ago (Santini, Kong, et al. 2013).

  • img-z33-5_03.gif

    Anguilloidei P. Bleeker 1859:xxxiii
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Anguilla anguilla (Linnaeus 1758), Moringua microchir Bleeker 1853a, and Serrivomer beanii T. N. Gill and Ryder 1883. This is a minimum-crown-clade definition.

  • Etymology. From the Latin Anguilla, meaning eel.

  • Registration number. 889.

  • Reference phylogeny. A phylogeny inferred from a concatenated dataset of DNA sequences from three nuclear genes and two mitochondrial protein coding genes (Santini, Kong, et al. 2013, fig. 2). See Figure 6 for a phylogeny of the major lineages of Anguilloidei.

  • Phylogenetics. Several molecular phylogenetic analyses result in the monophyly of Anguilloidei, with Moringuidae resolved as the sister lineage of all other anguilloids (Santini, Kong, et al. 2013; K. L. Tang and Fielitz 2013; Poulsen et al. 2018). The lineages previously classified as Lyomeri, Saccopharyngiformes, or Saccopharyngoidei are nested in Anguilloidei, but analyses differ on the monophyly of a group containing Monognathidae, Cyematidae, Saccopharyngidae, Neocyematidae, and Eurypharyngidae (Santini, Kong, et al. 2013; Poulsen et al. 2018).

  • Composition. Anguilloidei currently contains 81 species (Fricke et al. 2023) classified in Anguillidae, Cyema, Eurypharynx, Monognathidae, Moringuidae, Nemichthyidae, Neocyema, Saccopharyngidae, and Serrivomeridae. Over the past 10 years no new living species of Anguilloidei have been described (Fricke et al. 2023).

  • Diagnostic apomorphies. There are no known morphological apomorphies for Anguilloidei.

  • Synonyms. Lyomeri (T. N. Gill and Ryder 1883:263–264; Jordan 1923:134; Garstang 1931:257; Böhlke 1966:603–610), Saccopharyngiformes (Berg 1940:439–440; McAllister 1968:88–89; C. R. Robins 1989:13–15), and Saccopharyngoidei (Greenwood et al. 1966:393; J. S. Nelson 2006:125; J. S. Nelson et al. 2016:149–150) are all partial synonyms of Anguilloidei.

  • Comments. Bleeker (1864c) applied Anguilloidei as a ranked taxonomic family to a group containing Anguilla anguilla and the fossil taxon †Paranguilla tigrina. Greenwood et al. (1966) classified all Anguilliformes that were not in their Saccopharyngoidei into Anguilloidei. On the basis of the resolution of clades in molecular phylogenetic analyses, K. L. Tang and Fielitz (2013) revised the classification of Anguilliformes with a new delimitation of Anguilloidei that is the basis of the definition presented here. Bayesian relaxed molecular clock analysis estimates the crown age of Anguilloidei between approximately 64 and 90 million years ago (Santini, Kong, et al. 2013).

  • img-z34-2_03.gif

    Muraenoidei L. J. F. J. Fitzinger 1832:332
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive clade that contains Muraena helena Linnaeus 1758, Myroconger compressus Günther 1870, and Pythonichthys microphthalmus (Regan 1912d). This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek µύραινα (mjƱɹɹ̍e͡Inә) that is the name of the Mediterranean Moray, Muraena helena (D. W. Thompson 1947:162–165).

  • Registration number. 890.

  • Reference phylogeny. A phylogeny inferred from a concatenated dataset of the mitochondrial 12S and 16S rRNA genes (K. L. Tang and Fielitz 2013, fig. 1). Phylogenetic relationships among the lineages of Muraenoidei are presented in Figure 6.

  • Phylogenetics. Molecular phylogenetic analyses resolve Muraenoidei as monophyletic, with Myroconger (thin eels) and Muraenidae (moray eels) as sister clades relative to Heterenchelyidae (Inoue et al. 2010; G. D. Johnson et al. 2012; Santini, Kong, et al. 2013; K. L. Tang and Fielitz 2013; Poulsen et al. 2018). Alternatively, a morphological analysis results in paraphyly of Muraenoidei, with the chlopsid Xenoconger fryeri (Fryer's False Moray) resolved as the sister lineage of Muraenidae relative to Myroconger (D. G. Smith 1984).

  • Composition. Muraenoidei currently contains 238 species (Fricke et al. 2023) classified in Heterenchelyidae (mud eels), Muraenidae, and Myroconger (K. L. Tang and Fielitz 2013). Over the past 10 years 23 new living species of Muraenoidei have been described (Fricke et al. 2023), composing 9.7% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Muraenoidei include (1) frontals not fused (J. S. Nelson et al. 2016), (2) reduction in gill arch elements (J. S. Nelson et al. 2016), (3) reduction of lateral line (J. S. Nelson et al. 2016), and (4) normal-sized eyes (J. S. Nelson et al. 2016).

  • Synonyms. There are no synonyms of Muraenoidei.

  • Comments. Müller (1845b) used Muraenoidei as a family group name in his classification of Teleostei. Muraenoidei was later treated as a suborder containing Chlopsidae (false morays), Muraenidae, and Myrocongridae (C. R. Robins 1989). Given the resolution of a clade containing Heterenchelyidae, Muraenidae, and Myroconger in molecular phylogenies (Inoue et al. 2010; G. D. Johnson et al. 2012; Santini, Kong, et al. 2013; Poulsen et al. 2018), K. L. Tang and Fielitz (2013, table II) revised the classification of Anguilliformes with a new delimitation of Muraenoidei that is the basis of the definition presented here. Bayesian relaxed molecular clock analysis estimates the crown age of Muraenoidei ranges between 60 and 90 million years ago (Santini, Kong, et al. 2013).

  • img-z34-15_03.gif

    Congroidei P. Bleeker 1864a:18 [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Conger conger (Linnaeus 1758), Conger oceanicus (Mitchill 1818a), Derichthys serpentinus T. N. Gill 1884b, Heteroconger hassi (Klausewitz and Eibl-Eibesfeldt 1959), and Ophichthys zophochir Jordan and Gilbert 1882a. This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek γόγγρoϛ (ɡ̍ͻŋɹo͡Ʊz), meaning conger eel, Latinized to conger (D. W. Thompson 1947:49–50).

  • Registration number. 891.

  • Reference phylogeny. A phylogeny inferred from a concatenated dataset of DNA sequences from three nuclear genes and two mitochondrial protein coding genes (Santini, Kong, et al. 2013, fig. 2). Although Conger conger is not included in the reference phylogeny, it resolves with other species of Conger in molecular phylogenetic analyses (J. N. Chen et al. 2014, figs. 1, 2). The relationships among the lineages of Congroidei are shown in Figure 6.

  • Phylogenetics. The lineages delimited here in Congroidei are consistently resolved as monophyletic in molecular phylogenetic analyses (Inoue et al. 2010; G. D. Johnson et al. 2012; Santini, Kong, et al. 2013; K. L. Tang and Fielitz 2013; Poulsen et al. 2018). Despite the strong support for monophyly of Congroidei, the phylogenetics is complicated by the nonmonophyly of Derichthyidae (narrowneck eels) and Congridae (conger eels) in the analyses. Molecular studies support monophyly of a lineage containing Colocongridae (shorttail eels), Congriscus (Congridae), and Derichthyidae (López et al. 2007; Santini, Kong, et al. 2013; Poulsen et al. 2018); however, Nessorhamphus (Derichthyidae) and Congriscus are sister lineages, and Derichthys is resolved as sister to Colocongridae (worm eels) (Santini, Kong, et al. 2013). There is poor support for many of these nodes in the molecular phylogenies, but a morphological analysis provides strong support for the monophyly of Derichthyidae and resolution of a clade containing Colocongridae, Congriscus, and Derichthyidae (da Silva et al. 2019). Species of Nettastomatidae (duckbill eels) and the Congridae subclade Congrinae form a clade (Santini, Kong, et al. 2013; Poulsen et al. 2018), but Nettastomatidae and Congrinae are both paraphyletic. The Congridae subclades Bathymyrinae and Heterocongrinae are resolved as a clade (Santini, Kong, et al. 2013; Poulsen et al. 2018), but Bathymyrinae is rendered paraphyletic by Heteroconger (Santini, Kong, et al. 2013). Muraenesocidae (pike congers) and Ophichthidae (snake eels) are both monophyletic and resolved as sister lineages (Santini, Kong, et al. 2013; Poulsen et al. 2018).

  • Composition. Congroidei currently contains 660 species (Fricke et al. 2023) classified in Congridae, Coloconger, Derichthyidae, Muraenesocidae, Nettastomatidae, and Ophichthidae. Over the past 10 years 81 new living species of Congroidei have been described (Fricke et al. 2023), comprising 12.3% of the living species diversity in the clade.

  • Diagnostic apomorphies. There are no known morphological apomorphies for Congroidei.

  • Synonyms. There are no synonyms for Congroidei.

  • Comments. Bleeker (1864a:18) applied Congroidei as a taxonomic family. Classifications of Anguilliformes in the 20th century delimited Congroidei as a more inclusive group than given here on the basis of the presence of fused frontal bones in the skull (C. R. Robins 1989; J. S. Nelson 1994). Given the results of molecular phylogenetic analyses (Santini, Kong, et al. 2013; Poulsen et al. 2018), K. L. Tang and Fielitz (2013, table II) revised the classification of Congroidei to include Chlopsidae, Congridae, Derichthyidae, Muraenesocidae, Nettastomatidae, and Ophichthidae, which is not followed here. Bayesian relaxed molecular clock analysis estimates the crown age of Congroidei between 64 and 90 million years ago (Santini, Kong, et al. 2013).

  • img-z35-10_03.gif

    Osteoglossomorpha P. H. Greenwood,
    D. E. Rosen, S. H. Weitzman, and G. S. Meyers
    1966:350, 354–358, 393–394
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Hiodon tergisus Lesueur 1818, Pantodon buchholzi Peters 1876, Notopterus notopterus (Pallas 1769), and Osteoglossum bicirrhosum (Cuvier 1829). This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek ὀστέoν (̍αːstIәn), meaning bone; γλῶσσα (ɡl̍ͻsә), meaning tongue; and µoρϕή (m̍ͻ͡ɹfiː), meaning form or shape.

  • Registration number. 892.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of 546 exons (Peterson et al. 2022, fig. 1e). Phylogenetic relationships of the major living lineages and fossil taxa of Osteoglossomorpha are shown in Figure 6. The placements of the fossil lineages in the phylogeny are based on analyses of morphological characters (J.-Y. Zhang 1998, 2006; G.-Q. Li and Wilson 1999; Xu and Chang 2009).

  • Phylogenetics. Several studies prior to the mid-1960s hinted at a close relationship among what are now considered the lineages of Osteoglossomorpha (Ridewood 1904, 1905; Garstang 1931; Gregory 1933:161–175; Gosline 1960, 1961; Greenwood 1963), but it was Greenwood et al. (1966) that named the group and solidified evidence for its monophyly. The monophyly of Osteoglossomorpha is supported in several morphological and molecular phylogenetic analyses and Hiodon (mooneyes) and Osteoglossiformes are consistently resolved as sister groups (G.-Q. Li and Wilson 1996, 1999; G.-Q. Li, Wilson, et al. 1997; J.-Y. Zhang 1998; Hilton 2003; Inoue et al. 2003a, 2009; Lavoué and Sullivan 2004; M. V. H. Wilson and Murray 2008; Santini et al. 2009; Xu and Chang 2009; Lavoué, Miya, Arnegard, et al. 2012; Betancur-R, Broughton, et al. 2013; Hilton and Lavoué 2018; Murray et al. 2018; Brito et al. 2020; Peterson et al. 2022).

  • Composition. Osteoglossomorpha currently contains 254 living species (Fricke et al. 2023) classified in Hiodon and Osteoglossiformes. There are several fossil lineages of Osteoglossomorpha that include pan-hiodontids †Plesiolycoptera and †Yanbiania (G.-Q. Li and Wilson 1996, 1999; J.-Y. Zhang 1998) and the pan-osteoglossiforms †Paralycoptera, †Jinanichthys, †Huashia, and †Kuntulunia (Jiangyong 1990; G.-Q. Li and Wilson 1996, 1999; J.-Y. Zhang 1998, 2006; Xu and Chang 2009; Murray et al. 2018). Details of the ages and locations of the fossil taxa are given in Appendix 1. Over the past 10 years 15 new living species of Osteoglossomorpha have been described (Fricke et al. 2023), comprising 5.9% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Osteoglossomorpha include (1) primary bite between parasphenoid and basihyal; however, this trait is an apomorphy for a more inclusive pan-osteoglossomorphs (Greenwood et al. 1966; G.-Q. Li and Wilson 1996), (2) supramaxilla absent (G.-Q. Li and Wilson 1996, 1999; J.-Y. Zhang 2006; Xu and Chang 2009), (3) fourth and fifth infraorbitals fused (G.-Q. Li and Wilson 1996, 1999; J.-Y. Zhang 1998), (4) last uroneural much shorter than first uroneural (J.-Y. Zhang 1998), (5) rectangular-shaped infraorbital bone (G.-Q. Li and Wilson 1999), (6) seven pelvic-fin rays (J.-Y. Zhang 2006), (7) nasal bones tubular and strongly curved (Hilton 2003), (8) supraorbital sensory canal ending in frontal bone (Hilton 2003; M. V. H. Wilson and Murray 2008), (9) ascending process of premaxilla not developed or slightly developed (Hilton 2003; M. V. H. Wilson and Murray 2008), (10) autopalatine bone absent (M. V. H. Wilson and Murray 2008), (11) supraorbital absent (Mirande 2017), (12) complete absence of epurals (Mirande 2017), (13) bony epipleurals absent (Mirande 2017), and (14) intestine coils to the left of the stomach (Mirande 2017).

  • Synonyms. Osteoglossi is a partial (Garstang 1931:256–257) and an ambiguous (Gosline 1960:358) synonym of Osteoglossomorpha. Osteoglossoidei (Gosline 1960:358) is an ambiguous synonym of Osteoglossomorpha.

  • Comments. The earliest fossil osteoglossomorphs include the pan-osteoglossiforms †Paralycoptera, †Jinanichthys, and †Huashia that date from the Aptian (121.4–113.2 Ma) in the Cretaceous of China. Bayesian relaxed molecular clock analyses of Osteoglossomorpha result in an average posterior crown age estimate of 234.4 million years ago, with the credible interval ranging between 212.4 and 259.0 million years ago (Peterson et al. 2022).

  • img-z37-2_03.gif

    Osteoglossiformes P. H. Greenwood 1963:408
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Pantodon buchholzi Peters 1876, Notopterus notopterus (Pallas 1769), and Osteoglossum bicirrhosum (Cuvier 1829). This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek ὀστέoν ('αːstIәn), meaning bone, and γλῶσσα (ɡl'ͻsә), meaning tongue. The suffix is from the Latin forma, meaning form, figure, or appearance.

  • Registration number. 896.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of 546 exons (Peterson et al. 2022, fig. 1e). Phylogenetic relationships among the major lineages of Osteoglossiformes are shown in Figure 6. The placements of the fossil taxa †Palaeonotopterus and †Laeliichthys in the phylogeny are based on analyses of morphological characters (Cavin and Forey 2001; Murray et al. 2018; Brito et al. 2020).

  • Phylogenetics. The monophyly of Osteoglossiformes is supported in several morphological and molecular phylogenetic analyses (Taverne 1979, 1998; G.-Q. Li and Wilson 1996, 1999; G.-Q. Li, Wilson, et al. 1997; Hilton 2003; Lavoué and Sullivan 2004; J.-Y. Zhang 2006; M. V. H. Wilson and Murray 2008; Inoue et al. 2009; Xu and Chang 2009; Lavoué et al. 2011; Lavoue, Miya, Arnegard, et al. 2012; Lavoué 2015, 2016; Murray et al. 2018; Brito et al. 2020; Peterson et al. 2022). Within Osteoglossiformes, there is consistent support for the monophyly of a lineage consisting of Notopteridae (featherfin knifefishes) and the clade Mormyroidea, which contains Mormyridae (elephantfishes) and Gymnarchus niloticus (Aba) (Taverne 1979, 1998; G.-Q. Li and Wilson 1996, 1999; G.-Q. Li, Wilson, et al. 1997; Lavoué and Sullivan 2004; M. V. H. Wilson and Murray 2008; Inoue et al. 2009; Lavoué et al. 2011; Lavoue, Miya, Arnegard, et al. 2012; Lavoué 2015, 2016; Murray et al. 2018; Peterson et al. 2022).

  • Morphological phylogenies differ on the resolution of Osteoglossidae (bonytongues) with Pantodon buchholzi (Butterflyfish) as either the sister lineage of all other osteoglossids (Bonde 1996; M. V. H. Wilson and Murray 2008; Xu and Chang 2009) or nested within Osteoglossidae as the sister lineage of a clade containing Osteoglossum and Scleropages (Taverne 1979, 1998; G.-Q. Li and Wilson 1996, 1999; G.-Q. Li, Grande, et al. 1997; G.-Q. Li, Wilson, et al. 1997; Hilton 2003; Brito et al. 2020). Most molecular phylogenies resolve Pantodon as distantly related to other Osteoglossidae as the sister lineage of all other Osteoglossiformes (Lavoué and Sullivan 2004; Inoue et al. 2009; Lavoué et al. 2011; Lavoue, Miya, Arnegard, et al. 2012; Lavoué 2015, 2016; Hughes et al. 2018; Peterson et al. 2022).

  • Mormyridae is the most species-rich lineage of Osteoglossiformes, with at least 227 species classified in 22 genera (Fricke et al. 2023). Biodiversity discovery is active in mormyrids, as 11% of the living species diversity in the clade was described over the past 10 years (Sullivan et al. 2016; Fricke et al. 2023). Molecular phylogenies inferred from Sanger-sequenced nuclear and mitochondrial genes do not confidently resolve relationships within Mormyridae, but do strongly indicate that Brienomyrus, Hippopotamyrus, Marcusenius, and Pollimyrus are paraphyletic (Sullivan et al. 2000, 2016; Levin and Golubtsov 2018). Phylogenomic analyses of Mormyridae result in resolved and well-supported phylogenies where Hippopotamyrus and Marcusenius are paraphyletic, but Pollimyrus is monophyletic (Peterson et al. 2022). The Cretaceous fossil taxon †Palaeonotopterus greenwoodi is resolved as the sister lineage of Mormyroidea (Mormyridae and Gymnarchus) in phylogenetic analyses of morphological characters (Hilton 2003; Murray et al. 2018; Brito et al. 2020).

  • Morphological and molecular phylogenetic analyses resolve a monophyletic Notopteridae (e.g., Inoue et al. 2009; Brito et al. 2020). Within notopterids, the Asian (Chitala and Notopterus) and African (Papyrocranus and Xenomystus) lineages are each monophyletic and resolved as sister clades (Inoue et al. 2009). Morphological phylogenetic analyses resolved the Cretaceous fossil taxon †Laeliichthys ancestralis from Brazil as the sister lineage of Arapaiminae (Heterotis and Arapaima) (G.-Q. Li and Wilson 1996, 1999; Taverne 1998); however, a more recent morphological analysis places †Laeliichthys as the sister lineage of Notopteridae (Brito et al. 2020).

  • Composition. Osteoglossiformes currently contains 254 living species (Fricke et al. 2023) that include Pantodon buchholzi, Gymnarchus niloticus, and species classified in Mormyridae, Notopteridae, and Osteoglossidae (Hilton 2003). Fossil taxa include the pan-mormyroid †Palaeonotopterus and pan-notopterid †Laeliichthys (Silva Santos 1985; Lundberg 1993; Forey 1997; Cavin and Forey 2001; Murray et al. 2018; Brito et al. 2020). The ages and locations of †Palaeonotopterus and †Laeliichthys are given in Appendix 1. Over the past 10 years 15 new living species of Osteoglossiformes have been described (Fricke et al. 2023), comprising 5.9% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Osteoglossiformes include (1) 15 or fewer primary branched caudal fin rays (G.-Q. Li and Wilson 1996; G.-Q. Li, Grande, et al. 1997; G.-Q. Li, Wilson, et al. 1997; Hilton and Britz 2010), (2) two or fewer uroneurals in caudal skeleton (G.-Q. Li and Wilson 1996; Wiley and Johnson 2010), (3) nasal bone gutterlike or subrectangular (G.-Q. Li and Wilson 1996; G.-Q. Li, Grande, et al. 1997; G.-Q. Li, Wilson, et al. 1997), (4) six or fewer hypurals in caudal skeleton (G.-Q. Li, Grande, et al. 1997; Xu and Chang 2009), (5) dorsal hypurals and ural centrum 2 fused (G.-Q. Li, Wilson, et al. 1997; M. V. H. Wilson and Murray 2008; Hilton and Britz 2010; Wiley and Johnson 2010), (6) epurals absent (Hilton 2003; M. V. H. Wilson and Murray 2008; Hilton and Britz 2010), (7) bony elements associated with second ventral gill arch present as processes on second hypobranchial (Xu and Chang 2009), (8) presence of one ossified pair of hypohyals (Xu and Chang 2009), and (9) palatine and ectopterygoid fused (Xu and Chang 2009).

  • Synonyms. There are no synonyms of Osteoglossiformes.

  • Comments. The first delimitation of Osteoglossiformes included Hiodon and excluded Mormyridae (Greenwood et al. 1966:394). The hypothesis that Hiodon was nested in the clade delimited here as Osteoglossiformes was supported in several studies (G. J. Nelson 1968; Greenwood 1973; Lauder and Liem 1983). The delimitation of Osteoglossiformes that includes all living species of Osteoglossomorpha except Hiodon tergisus and H. alosoides was first proposed by Taverne (1979), and this hypothesis is corroborated in nearly all subsequent morphological and molecular phylogenetic analyses (e.g., G.-Q. Li and Wilson 1996; Lavoué and Sullivan 2004; Peterson et al. 2022).

  • The earliest fossil taxon of Osteoglossiformes is the pan-notopterid †Laeliichthys ancestralis from the Barremian (126.5–121.4 Ma) in the Cretaceous of Brazil (Silva Santos 1985; Brito et al. 2020). Bayesian relaxed molecular clock analyses of Osteoglossiformes result in an average posterior crown age estimate of 197.7 million years ago, with the credible interval ranging between 174.4 and 221.6 million years ago (Peterson et al. 2022).

  • img-z38-8_03.gif

    Osteoglossidae C. L. Bonaparte 1845:387
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Osteoglossum bicirrhosum (Cuvier 1829) and Heterotis niloticus (Cuvier 1829), but not Pantodon buchholzi Peters 1876. This is a minimum-crown-clade definition with an external specifier.

  • Etymology. From the ancient Greek ὀστέoν (̍αːstIәn), meaning bone, and γλῶσσα (ɡl̍ͻsә), meaning tongue.

  • Registration number. 897.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of complete mitochondrial genomes (Lavoué 2015, fig. 2). Phylogenetic relationships among the living lineages and fossil taxa of Osteoglossidae are presented in Figure 6. The placements of the fossil taxa in the phylogeny are on the basis of inferences from morphological characters (G.-Q. Li and Wilson 1996, 1999; J.-Y. Zhang 1998, 2006; Hilton 2003; Xu and Chang 2009; Murray et al. 2018).

  • Phylogenetics. Morphological and molecular analyses differ on the phylogenetic resolution of Pantodon buchholzi and Osteoglossidae. All morphological analyses resolve Pantodon either as the sister lineage of all other Osteoglossidae (G. J. Nelson 1969b; Greenwood 1973; Bonde 1996; M. V. H. Wilson and Murray 2008; Murray et al. 2018) or as the sister lineage of Osteoglossinae (G. J. Nelson 1968; Taverne 1979, 1998; G.-Q. Li and Wilson 1996, 1999; G.-Q. Li, Grande, et al. 1997; G.-Q. Li, Wilson, et al. 1997; Taverne 1998; J.-Y. Zhang 2006; Murray et al. 2018), which is a clade containing Osteoglossum and Scleropages (Hilton and Lavoué 2018). Molecular analyses agree with morphological studies in resolving two sets of sister lineages within Osteoglossidae: Osteoglossinae (Osteoglossum and Scleropages) and Arapaiminae (Arapaima and Heterotis); however, most molecular phylogenies place Pantodon as the sister lineage of all other Osteoglossiformes, distantly related to Osteoglossidae (Lavoué and Sullivan 2004; Inoue et al. 2009; Lavoué et al. 2011; Lavoue, Miya, Arnegard, et al. 2012; Lavoué 2015, 2016; Hughes et al. 2018; Peterson et al. 2022).

  • Composition. Osteoglossidae currently contains 12 living species (D. J. Stewart 2013a, 2013b; Fricke et al. 2023) that include Heterotis niloticus (African Arowana) and species classified in Arapaima, Osteoglossum, and Scleropages. Fossil lineages of Osteoglossidae include the pan-arapaimines †Joffrichthys and †Sinoglossus and the pan-osteoglossines †Cretophareodus, †Phareodus, and †Singida (G.-Q. Li and Wilson 1996, 1999; J.-Y. Zhang 1998, 2006; Hilton 2003; Xu and Chang 2009; Murray et al. 2018). The ages and locations of the fossil osteoglossids are given in Appendix 1. Over the past 10 years no new living species of Osteoglossidae have been described (Fricke et al. 2023).

  • Diagnostic apomorphies. Morphological apomorphies for Osteoglossidae include (1) six hypurals in caudal skeleton (G.-Q. Li and Wilson 1996), (2) opercle oval or kidney- shaped (G.-Q. Li and Wilson 1996; G.-Q. Li, Grande, et al. 1997), (3) palatoquadrate area behind and below orbit completely covered by infraorbitals (G.-Q. Li and Wilson 1996; G.-Q. Li, Grande, et al. 1997; Hilton 2003; J.-Y. Zhang 2006; M. V. H. Wilson and Murray 2008; Forey and Hilton 2010), (4) ventral part of preopercle does not reach level of orbit (G.-Q. Li, Wilson, et al. 1997; M. V. H. Wilson and Murray 2008), (5) basipterygoid process present (G.-Q. Li, Wilson, et al. 1997; Hilton 2003), (6) no connection between swim bladder and ear (G.-Q. Li, Wilson, et al. 1997; Forey and Hilton 2010), (7) supraorbital canal ending in frontal (G.-Q. Li and Wilson 1999; Forey and Hilton 2010), (8) extrascapular bone reduced and irregularly shaped (Hilton 2003; M. V. H. Wilson and Murray 2008; Forey and Hilton 2010), (9) nasal bones flat and broad (Hilton 2003; Forey and Hilton 2010), tooth plates of basibranchial and basihyal continuous (Hilton 2003), (10) subopercle small and anterior to opercle (Hilton 2003; J.-Y. Zhang 2006; Forey and Hilton 2010), (11) scales with reticulate furrows present over entire scale (Hilton 2003; Forey and Hilton 2010), (12) infraorbitals 3 and 4 fused (J.-Y. Zhang 2006), (13) temporal fossa present, bordered by epioccipital and pterotic (Xu and Chang 2009), and (14) first parapophysis expanded (Forey and Hilton 2010).

  • Synonyms. There are no synonyms of Osteoglossidae.

  • Comments. Bonaparte's (1845) introduction of the name Osteoglossidae was in a list of taxonomic names in a classification of fishes with no comment. Günther's (1868:377–380) delimitation of Osteoglossidae is identical to that presented here.

  • Osteoglossidae is a valid family-group name under the International Code of Zoological Nomenclature (Van der Laan et al. 2014:64). The earliest fossil taxon included in Osteoglossidae is †Cretophareodus alberticus from the Campanian (83.2–72.2 Ma) in the Cretaceous of Canada (G.-Q. Li 1996; Arbour et al. 2009). Bayesian relaxed molecular clock analyses of Osteoglossidae result in an average posterior crown age estimate of 96.6 million years ago, with the credible interval ranging between 78.6 and 112.7 million years ago (Peterson et al. 2022).

  • img-z40-3_03.gif

    Clupeocephala P. H. Greenwood 1973:326
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Clupea harengus Linnaeus 1758 (Otocephala, Clupeiformes), Engraulis encrasicolus (Linnaeus 1758) (Otocephala, Clupeiformes), Cyprinus carpio Linnaeus 1758 (Otocephala, Cypriniformes), Lepidogalaxias salamandroides Mees 1961 (Euteleostei), and Perca fluviatilis Linnaeus 1758 (Euteleostei, Perciformes). This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek ϰλoυπαῖα (kluːpi͡ә), a name with an obscure origin for an uncertain number of fish species used by ancient authors such as Plutarch (D. W. Thompson 1947:117–118) and ϰεϕαλή (kεfˈαːlә), meaning the head of a human or other animal.

  • Registration number. 898.

  • Reference phylogeny. A phylogeny inferred from DNA sequences sampled from 1,105 exons (Hughes et al. 2018, fig. S2). Phylogenetic relationships among the major living lineages and fossil taxa of Clupeocephala are shown in Figure 7. The resolutions of the fossil taxa in the phylogeny are on the basis of inferences from morphology (Taverne 1981; Gayet 1994; Fielitz 2002; de Figueiredo and Gallo 2004; de Figueiredo 2005; Gallo et al. 2009; de Figueiredo, Gallo, and Delarmelina, et al. 2012a; Guinot and Cavin 2018).

  • Phylogenetics. Clupeocephala was identified as the clade containing all living teleosts to the exclusion of Elopomorpha and Osteoglossomorpha (Patterson and Rosen 1977). Monophyly of Clupeocephala is consistently supported; however, the delimitation of lineages within the clade and hypotheses of their relationships vary among molecular and morphological phylogenetic analyses (Lê et al. 1993; Lecointre 1995; G. D. Johnson and Patterson 1996; Lecointre and Nelson 1996; Arratia 1997, 2018; Ishiguro et al. 2003; Lavoué et al. 2005; Poulsen et al. 2009; Near, Eytan, et al. 2012; Faircloth et al. 2013; Hughes et al. 2018; Straube et al. 2018; Musilova et al. 2019; Roth et al. 2020; Mu et al. 2022). In addition to morphological and molecular phylogenetic analyses, the conservation of gene adjacency in the genome and the proportion of shared chromosomal breakpoints support monophyly of Clupeocephala (Parey et al. 2023).

  • Composition. Clupeocephala currently contains more than 33,675 living species (Fricke et al. 2023) classified in Otocephala and Euteleostei (Near, Eytan, et al. 2012; Dornburg and Near 2021). Fossil lineages of Clupeocephala include the pan-euteleosts †Avitosmerus, †Beurlenichthys, †Erichalcis, †Gaudryella, †Ghabouria, †Helgolandichthys, †Parawenzichthys, †Santanasalmo, †Scombroclupeoides, †Wenzichthys, and †Tchernovichthys (Taverne 1981; Gayet 1994; Fielitz 2002; de Figueiredo 2005; Gallo et al. 2009; de Figueiredo, Gallo, and Delarmelina, et al. 2012; Guinot and Cavin 2018). Details of the ages and locations of fossil lineages are presented in Appendix 1. Over the past 10 years there have been 3,518 new living species of Clupeocephala described, comprising 10.5% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Clupeocephala include (1) autopalatine bone ossifies early in ontogeny (Arratia 2010a), (2) hypohyals pierced by hyoidean arteries (Arratia 2010a), (3) tooth plate of cartilaginous fourth pharyngobranchial element forms by the growth of only one tooth plate (Arratia 2010a), (4) uroneurals not inclined toward horizontal plane, but aligned at different angles (Arratia 2010a), (5) angular and articular bones fused (Arratia 2010a), (6) retroarticular bone excluded from articular facet of quadrate (Arratia 2010a), (7) absence of tooth plates on pharyngobranchial 1 (Arratia 2010a), (8) absence of tooth plates on pharyngobranchial 2 (Arratia 2010a), (9) absence of tooth plates on pharyngobranchial 3 (Arratia 2010a), (10) six or fewer hypurals (Arratia 2010a), and (11) fusion of duplicated chromosomes 2a and 2b (Parey et al. 2023).

  • Synonyms. There are no synonyms of Clupeocephala.

  • Comments. In defining Clupeocephala as all living teleosts to the exclusion of Elopomorpha and Osteoglossomorpha, Patterson and Rosen (1977) provided a resolution to the long-standing uncertainly regarding the relationships of Clupeiformes that was left unresolved in Greenwood et al. (1966). The composition of Clupeocephala has not changed subsequent to its introduction by Patterson and Rosen (1977). The earliest fossil taxon in Clupeocephala that is not an otocephalan is the pan-euteleost †Tchernovichthys exspectatum from the Hauterivian (132.6–126.5 Ma) in the Cretaceous of Israel (Gayet 1994). Bayesian relaxed molecular clock analyses of Clupeocephala result in an average posterior crown age estimate of 224.8 million years ago, with the credible interval ranging between 210.8 and 236.6 million years ago (Hughes et al. 2018).

  • img-z42-4_03.gif

    FIGURE 7.

    Phylogenetic relationships of the major living lineages and fossil taxa of Clupeocephala, Euteleostei, Argentiniformes, Salmoniformes, Esocidae, Stomiatii, Osmeriformes, and Stomiiformes. Filled circles identify the common ancestor of clades, with formal names defined in the clade accounts. Open circles highlight clades with informal group names. Fossil lineages are indicated with a dagger (†). Details of the fossil taxa are presented in Appendix 1.

    img-z41-1_03.jpg

    Otocephala G. D. Johnson and C. Patterson 1996:315
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Engraulis encrasicolus (Linnaeus 1758) (Clupeiformes), Gonorynchus greyi (Richardson 1845) (Gonorynchiformes), and Cyprinus carpio Linnaeus 1758 (Cypriniformes). This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek ώτός (h̍o͡Ʊt̍o͡Ʊz), meaning of the ear (the genitive declension of όυς), and ϰεϕαλή (kεf̍αːlә), meaning the head of a human or other animal.

  • Registration number. 899.

  • Reference phylogeny. A maximum likelihood phylogeny inferred from DNA sequences sampled from whole mitochondrial genomes (Poulsen et al. 2009, fig. 2). Phylogenetic relationships among the major lineages of Otocephala are shown in Figure 8. The placement of the fossil lineages †Ellimmichthyiformes, †Santanaclupea, and †Tischlingerichthys in the phylogeny reflects inferences based on morphology (Arratia 1997; Taverne 1997a; Forey 2004; Zaragüeta-Bagils 2004; Diogo 2007; Alvarado-Ortega et al. 2008; Mayrinck et al. 2015a; Vernygora et al. 2016; Vernygora 2020; Marramà et al. 2023).

  • Phylogenetics. The first phylogenies supporting monophyly of Clupeocephala resolved Clupeiformes and Euteleostei as sister groups, with Ostariophysi included in Euteleostei (Patterson and Rosen 1977). The monophyly of Otocephala as a group containing Ostariophysi and Clupeiformes to the exclusion of Euteleostei was a discovery resulting from early molecular phylogenetic analyses of gnathostomes (Lê et al. 1993), but subsequently supported in several morphological phylogenetic analyses and reviews of morphological synapomorphies (Arratia 1996b, 1997, 1999; G. D. Johnson and Patterson 1996; Lecointre and Nelson 1996). Phylogenetic analyses of DNA sequences from whole mitochondrial genomes resulted in an unexpected expansion of Otocephala to include the deep-sea Alepocephaliformes (Ishiguro et al. 2003; Lavoué et al. 2005, 2007; Lavoué, Miya, Kawaguchi, et al. 2008), historically classified within Euteleostei as Argentiniformes (e.g., Greenwood and Rosen 1971; A. C. Gill and Mooi 2002; J. S. Nelson 2006:192–194). The monophyly of the expanded Otocephala and the resolution of Alepocephaliformes and Ostariophysi as sister lineages is supported in molecular phylogenetic analyses of nuclear genes, combinations of mitochondrial and nuclear genes, and a phylogenomic analysis of DNA sequences sampled from more than 800 exons (Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; W.-J. Chen et al. 2013; Straube et al. 2018). Investigations of morphological characters identify apomorphies consistent with the delimitation of Otocephala presented here (Arratia 2018; Straube et al. 2018).

  • Composition. Otocephala currently contains 12,270 living species (Fricke et al. 2023) classified in Alepocephaliformes, Clupeiformes, and Ostariophysi. Fossil lineages of Otocephala include the pan-clupeiforms †Ellimmichthyiformes and †Santanaclupea and the pan-ostariophysan †Tischlingerichthys (L. Grande 1985; Maisey 1993; Arratia 1997; M.-M. Chang and Maisey 2003; Zaragüeta-Bagils 2004; Alvarado-Ortega et al. 2008, 2020; de Figueiredo 2009; Murray and Wilson 2013; Vernygora 2020; Marramà et al. 2023). Over the past 10 years 1,729 new living species of Otocephala have been described (Fricke et al. 2023), comprising 14.1% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Otocephala include (1) parietals fused with extrascapulars, with an uncertain distribution in Alepocephaliformes (Lecointre and Nelson 1996; Arratia 2018; Straube et al. 2018), (2) anterior part of swim bladder with silvery peritoneum (Fink and Fink 1996; Straube et al. 2018), but Alepocephaliformes lack a swim bladder (Arratia 2018; Straube et al. 2018), and (3) haemal spines anterior of preural centrum 2 fuse with their centra from an early point in development (Arratia 2018; Straube et al. 2018).

  • Synonyms. Otomorpha (Wiley and Johnson 2010:134; Betancur-R et al. 2017:14–15) and Ostarioclupeomorpha (Arratia 1997:155) are ambiguous synonyms of Otocephala.

  • Comments. G. D. Johnson and Patterson (1996) applied the group name Otocephala to the clade containing Clupeiformes and Ostariophysi, which was initially discovered in one of the earliest molecular data to investigate teleost phylogeny (Lê et al. 1993). Molecular phylogenetic analyses led to the expansion of Otocephala to include Alepocephaliformes (Ishiguro et al. 2003; Near, Eytan, et al. 2012; Straube et al. 2018). The name Otocephala was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade.

  • The earliest fossil otocephalan lineages include the pan-ostariophysan †Tischlingerichthys from the Tithonian (149.2–143.1 Ma) in the Jurassic of Germany (Arratia 1997, 2001). Bayesian relaxed molecular clock analyses of Otocephala result in an average posterior crown age estimate of 194.5 million years ago, with the credible interval ranging between 179.7 and 211.2 million years ago (Hughes et al. 2018).

  • img-z44-8_03.gif

    FIGURE 8.

    Phylogenetic relationships of the major living lineages and fossil taxa of Otocephala, Clupeiformes, Clupeoidei, Alepocephaliformes, Ostariophysi, Gonorynchiformes, Otophysi, Gymnotiformes, Pan-Siluriformes, and Cithariniformes. Filled circles identify the common ancestor of clades, with formal names defined in the clade accounts. Open circles highlight clades with informal group names. Fossil lineages are indicated with a dagger (†). Details of the fossil taxa are presented in Appendix 1. The clade description of Pan-Siluriformes is presented in Lundberg (2020c).

    img-z43-1_03.jpg

    Clupeiformes E. S. Goodrich 1909:386
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Denticeps clupeoides Clausen 1959, Clupea harengus Linnaeus 1758, and Engraulis encrasicolus (Linnaeus 1758). This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek ϰλoυπαα (kl̍uːpi͡ә), a name with an obscure origin for an uncertain number of fish species used by ancient authors such as Plutarch (D. W. Thompson 1947:117–118). The suffix is from the Latin forma, meaning form, figure, or appearance.

  • Registration number. 900.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of 1,165 exons (Q. Wang et al. 2022, fig. 2). Phylogenetic relationships among the living and fossil lineages of Clupeiformes are shown in Figure 8. The fossil lineages †Cynoclupea and †Paleodenticeps are placed in the phylogeny on the basis of inferences from morphology (Greenwood 1960, 1968; Malabarba and Di Dario 2017; Vernygora 2020).

  • Phylogenetics. Greenwood et al. (1966) delimited Clupeiformes to include Denticeps clupeoides and Clupeoidei, which is reflected in subsequent classifications (G. J. Nelson 1970b; L. Grande 1985; Lavoué, Konstantinidis, et al. 2014; J. S. Nelson et al. 2016:164–172; Betancur-R et al. 2017). A consistent result in morphological and molecular phylogenetic analyses of Clupeiformes is the resolution of Clupeoidei and Denticeps as sister groups (G. J. Nelson 1967, 1970b; Patterson and Rosen 1977; L. Grande 1985; Lavoué et al. 2007; de Pinna and Di Dario 2010; Lavoué, Konstantinidis, et al. 2014; Straube et al. 2018; Vernygora 2020; Milec et al. 2022; Q. Wang et al. 2022).

  • Composition. Clupeiformes currently contains 448 living species that include Denticeps clupeoides and species classified in Clupeoidei (Lavoué, Konstantinidis, et al. 2014; Q. Wang et al. 2022; Fricke et al. 2023). Fossil lineages of Clupeiformes include the pan-clupeoid †Cynoclupea (Malabarba and Di Dario 2017) and the pan-denticipitid †Paleodenticeps (Greenwood 1960). Details of the ages and locations of †Cynoclupea and †Paleodenticeps fossil taxa are given in Appendix 1. Over the past 10 years 43 new living species of Clupeiformes have been described (Fricke et al. 2023), comprising 9.6% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Clupeiformes include (1) presence of abdominal scutes (Whitehead 1962; Patterson 1970; L. Grande 1985; Wiley and Johnson 2010), (2) diverticulum of swim bladder penetrates exoccipital, expanding to form ossified bulla in prootic or pterotic (Greenwood et al. 1966; L. Grande 1985; Wiley and Johnson 2010), (3) presence of recessus lateralis where infraorbital canal merges with preopercular canal (Greenwood et al. 1966; Greenwood 1968; L. Grande 1982, 1985; T. Grande and de Pinna 2004; Zaragüeta-Bagils 2004), (4) supraoccipital completely separates parietals (Whitehead 1962; Patterson 1970; L. Grande 1982, 1985; Zaragüeta-Bagils 2004), (5) absence of basipterygoid process of parasphenoid (Zaragüeta-Bagils 2004), (6) third preural centrum with thin haemal spine (Zaragüeta-Bagils 2004), and (7) presence of sensory cephalic canal branch that originates at junction between extrascapular bone and recessus lateralis (Di Dario and de Pinna 2006).

  • Synonyms. Clupeomorpha (Greenwood et al. 1966:358–-361) and Clupei (Wiley and Johnson 2010:134–135; Betancur-R et al. 2017:15) are ambiguous synonyms of Clupeiformes.

  • Comments. When first delimited, Clupeiformes was a “purely artificial assemblage of lowly organised (sic) families (Goodrich 1909:386)” and included clupeiforms as well as lineages now classified as Elopomorpha, Osteoglossomorpha, Salmonidae, Gonorynchiformes, Alepocephaliformes, and Stomiiformes. Greenwood et al. (1966) dismantled the groups Isospondyli and Malacopterygii (e.g., Boulenger 1904a; Bigelow 1963), limiting Clupeiformes to Clupeoidei and Denticeps. The name Clupeiformes was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade.

  • The earliest fossil Clupeiformes is the pan-clupeoid †Cynoclupea from the Barremian-Aptian (129.4–113.0 Ma) in the Cretaceous of Brazil, which was initially placed as the sister lineage of a clade containing Chirocentridae and Engraulidae (Malabarba and Di Dario 2017). However, Engraulidae is the sister lineage of all other Clupeoidei, and Chirocentridae shares common ancestry with Pristigasteridae (Vernygora 2020). The shared character states with both Engraulidae and Pristigasteridae indicate †Cynoclupea is best resolved as a pan-clupeoid (Malabarba and Di Dario 2017). Bayesian relaxed molecular clock analyses of Clupeiformes result in an average posterior crown age estimate of 130.8 million years ago, with the credible interval ranging between 125.5 and 138.9 million years ago (Q. Wang et al. 2022).

  • img-z46-1_03.gif

    Clupeoidei P. Bleeker 1849:6
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Spratelloides gracilis (Temminck and Schlegel 1846), Clupea harengus Linnaeus 1758, and Engraulis encrasicolus (Linnaeus 1758), but not Denticeps clupeoides Clausen 1959. This is a minimum-crown-clade definition with an external specifier.

  • Etymology. From the ancient Greek ϰλoυπαῖα (kl̍uːpi͡ә), a name with an obscure origin for an uncertain number of fish species used by ancient authors such as Plutarch (D. W. Thompson 1947:117–118).

  • Registration number. 901.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of 1,165 exons (Q. Wang et al. 2022, fig. 2). See Figure 8 for a phylogeny of the living and fossil lineages comprising Clupeoidei. The placements of fossil lineages in the phylogeny are based on inferences from morphology (Taverne 2002, 2004, 2007a, 2007b, 2011a; Marramà and Carnevale 2018).

  • Phylogenetics. Greenwood et al. (1966) grouped all living species of Clupeiformes in Clupeoidei except Denticeps clupeoides. On the basis of gill arch morphology, G. J. Nelson (1967, 1970b) delimited four lineages of Clupeoidei: Chirocentridae (wolf herrings), Clupeidae (shads and sardines), Engraulidae (anchovies), and Pristigasteridae (longfin herrings). Analyses of morphological characters and molecular phylogenetic studies consistently support the monophyly of Clupeoidei (L. Grande 1985; Di Dario 2004; Lavoué et al. 2007, 2013; Li and Ortí 2007; Lavoué, Miya, Kawaguchi, et al. 2008; de Pinna and Di Dario 2010; Bloom and Lovejoy 2014; Lavoué, Konstantinidis, et al. 2014; Bloom and Egan 2018; Egan et al. 2018; Milec et al. 2022; Q. Wang et al. 2022); however, the traditional delimitation of Clupeidae is not resolved as monophyletic (e.g., Lavoué, Konstantinidis, et al. 2014; Egan et al. 2018; Vernygora 2020). The lack of clupeid monophyly has prompted the recognition of the lineages Alosidae (shads), Dorosomatidae (gizzard shads), Dussumieriidae (round herrings), Ehiravidae (ehiravines), and Spratelloididae (small round herrings) (Bloom and Egan 2018; Vernygora 2020; Q. Wang et al. 2022). Traditionally, Dussumieriidae included Dussumieria and Etrumeus (Whitehead 1985; J. S. Nelson et al. 2016:170), but phylogenomic analysis resolves Dussumieria and Chirocentrus as sister lineages and Etrumeus as the sister lineage of all sampled species of Clupeidae (Q. Wang et al. 2022).

  • Molecular phylogenies inferred from combinations of Sanger-sequenced mitochondrial and nuclear genes and phylogenomic analysis of 1,165 exons resolve Spratelloididae as the sister lineage of all other Clupeoidei (Bloom and Egan 2018; Egan et al. 2018; Q. Wang et al. 2022). Morphological characters seem to support Chirocentridae and Engraulidae as sister groups (Di Dario 2009; Malabarba and Di Dario 2017; Vernygora 2020, figs. 6, 7), but molecular phylogenies place Chirocentrus as the sister lineage to Pristigasteridae (Bloom and Egan 2018; Egan et al. 2018; Vernygora 2020, figs. 6–9). A morphological phylogenetic analysis of 175 characters sampled from 101 clupeiform species resulted in unresolved relationships with poor node support (Vernygora 2020, figs. 6, 7).

  • Composition. Clupeoidei currently contains 447 living species (Fricke et al. 2023) classified in Alosidae, Chirocentrus, Clupeidae, Dorosomatidae, Dussumieria, Ehiravidae, Engraulidae, Pristigasteridae, and Spratelloididae (Q. Wang et al. 2022). Fossil clupeoids include the pan-clupeids †Italoclupea and †Lecceclupea (Taverne 2007a, 2011a), the pan-dussumieriids †Nardoclupea and †Portoselvaggioclupea (Taverne 2002, 2007b), and the pan-alosids †Eoalosa and †Pugliaclupea (Taverne 2004; Marramà and Carnevale 2018). Details regarding the ages and locations of the fossil taxa are given in Appendix 1. Over the past 10 years 43 new living species of Clupeoidei have been described (Fricke et al. 2023), comprising 9.6% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Clupeoidei include (1) first uroneural and first preural fused (L. Grande 1985; Zaragüeta-Bagils 2004), (2) relative size of first ural centrum reduced (L. Grande 1985; Zaragüeta-Bagils 2004), (3) absence of lateral line scales (L. Grande 1985; Vernygora 2020), (4) parhypural and first ural centrum separated (L. Grande 1985; Zaragüeta-Bagils 2004), (5) absence of a complete series of ventral scutes between isthmus and anus (Zaragüeta-Bagils 2004), (6) ventral limb of hyomandibula and quadrate separated by metapterygoid (Di Dario 2009; Vernygora 2020), (7) single row of gill rakers on first through third arches (de Pinna and Di Dario 2010), (8) close proximity of dorsal gill arch elements to the midline (de Pinna and Di Dario 2010), (9) second and third infrapharyngobranchials produced anteriorly as a narrow long process (de Pinna and Di Dario 2010), and (10) presence of notch on third hypural (Vernygora 2020).

  • Synonyms. There are no synonyms of Clupeoidei.

  • Comments. Clupeoidei is among the most economically important lineages of fishes (FAO 2020). The generation of phylogenomic datasets that include hundreds of clupeoid species is a major priority for future teleost phylogenetics. This priority goes beyond the inherent interest in resolving this portion of the tree of life and is justified by the clade's economic importance and growing conservation concerns (FAO 2020; Birge et al. 2021).

  • Fossil taxa phylogenetically nested within crown subclades of Clupeoidei include †Knightia eocaena in Clupeidae, †Chasmoclupea aegyptica and †Trollichthys bolcensis in Spratelloididae, and †Eoengraulis fasoloi in Engraulidae (Vernygora 2020). The earliest fossil lineage of Clupeoidei is †Audenaerdia casieri with an uncertain phylogenetic resolution with Clupeidae or Alosidae from the Santonian (85.7–83.2 Ma) in the Cretaceous (Taverne 1997a, 1997b). The earliest Clupeoidei fossil lineages with a more confident phylogenetic resolution include the pan-clupeids †Italoclupea and †Lecceclupea (Taverne 2007a, 2011a), the pan-dussumieriids †Nardoclupea and †Portoselvaggioclupea (Taverne 2007b), and the pan-alosid †Pugliaclupea (Taverne 2004) from the Campanian-Maastrichtian (83.26–66.0 Ma) in the Cretaceous. Bayesian relaxed molecular clock analyses of Clupeoidei result in an average posterior crown age estimate of 91.4 million years ago, with the credible interval ranging between 76.1 and 107.3 million years ago (Q. Wang et al. 2022).

  • img-z47-6_03.gif

    Alepocephaliformes N. B. Marshall 1962:265
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Alepocephalus rostratus Risso 1820, Alepocephalus bairdii Goode and Bean 1879, Bathylaco nigricans Goode and Bean 1896, and Platytroctes apus Günther 1878b. This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek λεπἴς (l̍εpIs), meaning the scale of a fish, with the prefix “a” meaning without scales and ϰεϕαλή (kεf̍αːlә) meaning the head of a human or other animal. The suffix is from the Latin forma, meaning form, figure, or appearance.

  • Registration number. 902.

  • Reference phylogeny. A phylogeny of Alepocephaliformes inferred from DNA sequences of complete mitochondrial genomes (Poulsen et al. 2009, fig. 3). Although Alepocephalus rostratus is not included in the reference phylogeny, it clusters with Xenodermichthys copei as the only sampled species of Alepocephaliformes in a DNA barcoding study (Landi et al. 2014, fig. S1). Phylogenetic relationships of Alepocephaliformes are shown in Figure 8.

  • Phylogenetics. The phylogenetic placement of Alepocephaliformes within Teleostei has shifted substantially over the past century, previously being grouped with Clupeiformes (Gregory and Conrad 1936), a delimitation of Salmoniformes that includes Salmonidae, Argentiniformes, Galaxiidae, Osmeriformes, Stomiiformes, and Esocidae (Greenwood et al. 1966; Markle 1976), and Osmeriformes (Gosline 1969). Greenwood and Rosen (1971) hypothesized Alepocephaliformes and Argentiniformes are sister lineages on the basis of a modified posterior pharyngobranchial structure they named the crumenal organ, which was the basis for the resolution of this clade in subsequent morphological studies (Begle 1992; G. D. Johnson and Patterson 1996). However, Ahlstrom et al. (1984) rejected the hypothesized common ancestry of Alepocephaliformes and Argentiniformes because alepocephaliform species hatch from larger eggs and exhibit direct development; additionally, the two lineages share no unique ontogenetic characters. Molecular phylogenetic analyses consistently resolve Alepocephaliformes in a clade with Clupeiformes and Ostariophysi (Ishiguro et al. 2003; Lavoué, Miya, Poulsen, et al. 2008; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; Straube et al. 2018), prompting the classification of these three clades in Otocephala.

  • Two morphological analyses of relationships within Alepocephaliformes result in very different phylogenetic trees, with all alepocephaliforms classified as Alepocephalidae (slickheads) in Begle (1992) and the resolution of Alepocephalidae and Platytroctidae (tubeshoulders) in G. D. Johnson and Patterson (1996). Molecular phylogenetic analyses of DNA sequences from whole mitochondrial genomes or combinations of mitochondrial and nuclear genes resolve Alepocephalidae and Platytroctidae each as monophyletic groups (Lavoué, Miya, Poulsen, et al. 2008; Poulsen et al. 2009; Betancur-R et al. 2017; Rabosky et al. 2018; Poulsen 2019), but one molecular analysis resulted in Platytroctidae nested within Alepocephalidae (Betancur-R et al. 2017).

  • Composition. There are currently 142 living species of Alepocephaliformes classified in Alepocephalidae and Platytroctidae (Fricke et al. 2023). Over the past 10 years two new living species of Alepocephaliformes have been described, accounting for 1.4% of the living species diversity in the clade.

  • Diagnostic apomorphies. The apomorphies of Alepocephaliformes are uncertain because of the reductive nature of morphological characters in the lineages and the fact that all morphological phylogenetic analyses assumed a relationship with Argentiniformes (Begle 1992; G. D. Johnson and Patterson 1996). Morphological apomorphies for Alepocephaliformes include (1) separation of parietals by supraoccipital (Greenwood and Rosen 1971; G. D. Johnson and Patterson 1996; Wiley and Johnson 2010), (2) absence of posttemporal fossa (Gosline 1969; G. D. Johnson and Patterson 1996; Wiley and Johnson 2010), (3) presence of branchiostegal cartilages (G. D. Johnson and Patterson 1996; Wiley and Johnson 2010), (4) reduction of dorsal portion of opercle (Begle 1992; G. D. Johnson and Patterson 1996; Wiley and Johnson 2010), (5) forward extension of ossified epipleural series to third vertebra (Patterson and Johnson 1995; G. D. Johnson and Patterson 1996; Wiley and Johnson 2010), (6) absence of urodermal (G. D. Johnson and Patterson 1996; Wiley and Johnson 2010), and (7) presence of single postcleithrum (Markle 1976; G. D. Johnson and Patterson 1996; Wiley and Johnson 2010).

  • Synonyms. Alepocephaloidei (Bleeker 1859:xxx; Wiley and Johnson 2010:141), Alepocephaloidea (Greenwood and Rosen 1971:39–40; Begle 1992:351; G. D. Johnson and Patterson 1996:312), and Alepocephali (Betancur-R et al. 2017:15) are ambiguous synonyms of Alepocephaliformes. Alepocephaloidei and Bathylaconoidei (Greenwood et al. 1966:394) are approximate synonyms of Alepocephaliformes.

  • Comments. Marshall (1962:265) applied the name Alepocephaliformes to the lineage comprising Alepocephalidae and Searsiidae, a synonym of Platytroctidae (Parr 1951; Van der Laan et al. 2014:58). Long considered a subclade of Argentiniformes (Greenwood and Rosen 1971; Begle 1992; G. D. Johnson and Patterson 1996), Alepocephaliformes is now placed with Clupeiformes and Ostariophysi in Otocephala (Near, Eytan, et al. 2012; Arratia 2018; Straube et al. 2018). The name Alepocephaliformes was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade.

  • The fossil record of Alepocephaliformes is relatively poor when compared with other lineages of Otocephala. The earliest skeletal fossils of Alepocephaliformes date to the Rupelian (33.9–28.1 Ma) in the Oligocene and the earliest otoliths are from the Ypresian (56.0–47.8 Ma) in the Eocene (Přikryl and Carnevale 2019). A maximum likelihood relaxed molecular clock analysis of Alepocephaliformes resulted in a crown age estimate of 38.8 million years ago (Rabosky et al. 2018).

  • img-z49-3_03.gif

    Ostariophysi M. Sagemehl 1885:22
    (as Ostariophysen) [Lundberg 2020]

  • Definition. Defined as a minimum-crown-clade in Lundberg (2020a) as: “The crown clade originating in the most recent common ancestor of Gonorynchus (originally Cyprinus) gonorynchus (Linnaeus 1766), Cyprinus carpio Linnaeus 1758 (Cypriniformes), Charax (originally Salmo) gibbosus (Linnaeus 1758) (Characiformes), Gymnotus carpio Linnaeus 1758 (Gymnotiformes; Gymnotoidei on the reference phylogeny), and Silurus glanis Linnaeus 1758 (Siluriformes; Siluroidei on the reference phylogeny).”

  • Etymology. From the ancient Greek ὀστἀριoν (ho͡Ʊst̍α͡ɹɹi͡әn), meaning little bone, and ϕῦσα (f̍uːsә), meaning bladder.

  • Registration number. 196.

  • Reference phylogeny. Fink and Fink (1981, fig. 1) was designated as the reference phylogeny by Lundberg (2020a). Phylogenetic relationships of the living and fossil lineages of Ostariophysi are presented in Figure 8. The placement of the pan-otophysan fossil lineages †Chanoides, †Clupavus, †Lusitanichthys, †Nardonoides, and †Santanichthys are on the basis of inferences from morphology (Patterson 1984a; Taverne 1995; Diogo et al. 2008; Diogo 2009; Malabarba and Malabarba 2010; Mayrinck 2011).

  • Phylogenetics. The monophyly of Ostariophysi as a lineage that includes Gonorynchiformes and Otophysi was first inferred from the morphology of the caudal skeleton and cervical vertebrae (Rosen and Greenwood 1970), a conclusion not universally accepted at the time (T. R. Roberts 1973). Subsequent summaries and phylogenetic analyses of morphological characters consistently resolve Ostariophysi as monophyletic (Fink and Fink 1981, 1996; Patterson 1984a, 1984b, 1994; Arratia 1999, 2000a, 2008, 2010b; Diogo et al. 2008). Early molecular phylogenetic analyses of whole mitochondrial genomes resolved Gonorynchiformes and Clupeiformes as sister lineages (Ishiguro et al. 2003; Saitoh et al. 2003; Peng et al. 2006). However, the monophyly of Ostariophysi is supported in all subsequent molecular phylogenetic studies that include analyses of whole mitochondrial genomes (Lavoué et al. 2005, 2007, 2010; Jondeung et al. 2007; Lavoué, Miya, Poulsen, et al. 2008; Poulsen et al. 2009; Nakatani et al. 2011; Davis et al. 2013), collections of Sanger-sequenced mitochondrial or nuclear genes (Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; W.-J. Chen et al. 2013), and phylogenomic datasets (Arcila et al. 2017; Chakrabarty et al. 2017; Dai et al. 2018; Hughes et al. 2018; Straube et al. 2018; Mu et al. 2022).

  • Composition. Ostariophysi currently contains 11,682 species (Fricke et al. 2023) classified in Gonorynchiformes and Otophysi. Fossil ostariophysans include the pan-otophysans †Chanoides, †Clupavus, †Lusitanichthys, †Nardonoides, and †Santanichthys (Patterson 1984a; Fink and Fink 1996; Cavin 1999; Filleul and Maisey 2004; Diogo et al. 2008; Malabarba and Malabarba 2010; Mayrinck 2011; Mayrinck et al. 2015b). Details regarding the ages and locations of the fossil taxa are listed in Appendix 1. Over the past 10 years there have been 1,686 new living species of Ostariophysi described (Fricke et al. 2023), comprising 14.4% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Ostariophysi include (1) sacculi and lagena situated posteriorly and along the midline (Rosen and Greenwood 1970; Fink and Fink 1981, 1996; Wiley and Johnson 2010; Lundberg 2020a), (2) swim bladder divided into small anterior and large posterior chamber (Rosen and Greenwood 1970; Fink and Fink 1981, 1996; Wiley and Johnson 2010), (3) anterior chamber of swim bladder covered with silvery peritoneal tunic (Rosen and Greenwood 1970; Fink and Fink 1981, 1996; Lundberg 2020a), (4) peritoneal tunic covering anterior chamber of swim bladder attached to two most anterior pleural ribs (Rosen and Greenwood 1970; Fink and Fink 1981, 1996; Wiley and Johnson 2010; Lundberg 2020a), (5) absence of basisphenoid (Fink and Fink 1981, 1996; Wiley and Johnson 2010; Lundberg 2020a), (6) absence of dermopalatine (Fink and Fink 1981, 1996; Wiley and Johnson 2010; Lundberg 2020a), (7) absence of supramaxillae (Fink and Fink 1981, 1996; Wiley and Johnson 2010), (8) dorsal mesentery suspending swim bladder thickened anterodorsally (Fink and Fink 1981, 1996; Wiley and Johnson 2010; Lundberg 2020a), (9) absence of supraneural or accessory neural arch anterior to first vertebra (Fink and Fink 1981, 1996; Lundberg 2020a), (10) presence of expanded anterior neural arches that form roof over neural canal (Fink and Fink 1981, 1996; Wiley and Johnson 2010; Lundberg 2020a), (11) absence of neural arch anterior to arch of first vertebral centrum (Fink and Fink 1981, 1996; Wiley and Johnson 2010; Lundberg 2020a), (12) haemal spines anterior to second preural centrum fused to centrum (Fink and Fink 1981, 1996), (13) presence of Schreckstoff pheromone, an alarm substance produced by epidermal cells, stimulating a fright reaction in conspecifics (Pfeiffer 1977; Fink and Fink 1981, 1996; Wiley and Johnson 2010; Lundberg 2020a), and (14) absence of supraneural 1 and its cartilaginous precursor (Hoffmann and Britz 2006; Wiley and Johnson 2010).

  • Synonyms. There are no synonyms of Ostariophysi.

  • Comments. Sagemehl (1885:22) applied the name Ostariophysen to a group consisting of Cypriniformes, Gymnotiformes, Siluriformes, Characiformes, and Cithariniformes, which are classified here as Otophysi. This more exclusive definition of Ostariophysi was maintained for nearly a century (Boulenger 1904b:573–596; Goodrich 1909:371; Regan 1911d, 1911e; Jordan 1923:134–153; Greenwood et al. 1966; Gosline 1971:120–124). Citing several shared morphological traits, Rosen and Greenwood (1970) expanded Ostariophysi to include Gonorynchiformes and placed Cypriniformes, Gymnotiformes, Siluriformes, and Characiformes (sensu lato) in Otophysi. The earliest fossil Ostariophysi is the pan-otophysan †Santanichthys diasii from the Aptian-Albian (121.4–100.5 Ma) in the Cretaceous of Brazil. Bayesian relaxed molecular clock analyses of Ostariophysi result in an average posterior crown age estimate of 160.6 million years ago, with the credible interval ranging between 154.2 and 169.6 million years ago (Hughes et al. 2018).

  • img-z50-5_03.gif

    Gonorynchiformes P. H. Greenwood,
    D. E. Rosen, S. H. Weitzman, and G. S. Myers
    1966:374 [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Gonorynchus gonorynchus (Linnaeus 1766), Gonorynchus greyi (Richardson 1845), Chanos chanos [Fabricius in Niebuhr (ex Forsskål) 1775], and Kneria paucisquamata Poll and Stewart 1975. This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek γωνία (ɡˈo͡Ʊniә), meaning angle, and ῤυγχoς (ɹˈuːɡko͡Ʊz), meaning snout or beak. The suffix is from the Latin forma, meaning form, figure, or appearance.

  • Registration number. 903.

  • Reference phylogeny. A time-calibrated phylogeny inferred from morphological characters and nine Sanger-sequenced nuclear genes (Near, Dornburg, and Friedman 2014, fig. 4). Although Gonorynchus gonorynchus is not included in the reference phylogeny, it resolves in a clade with four other species of Gonorynchus, including G. greyi, in a phylogenetic analysis of morphological characters (T. Grande 1999, fig. 10). Phylogenetic relationships among living and fossil lineages of Gonorynchiformes are shown in Figure 8. The placement of fossil lineages in the phylogeny is on the basis of analyses of morphological characters (Gayet 1993; T. Grande 1994, 1996; T. Grande and Poyato-Ariza 1999; Poyato-Ariza et al. 2010; Near, Dornburg, and Friedman 2014; Ribeiro, Poyato-Ariza, et al. 2018).

  • Phylogenetics. The first studies of relationships within Gonorynchiformes differed as to the earliest divergences in the clade. Greenwood et al. (1966) hypothesized that Gonorynchus was the likely sister lineage to all other gonorynchiforms, but Rosen and Greenwood (1970) argued that Chanos is the least morphologically specialized lineage of Gonorynchiformes and presented a classification reflecting this hypothesis.

  • Phylogenetic analyses using morphological characters have frequently included fossil lineages and all resolve Chanos as the living sister lineage of all other Gonorynchiformes (Patterson 1984b; Blum 1991; Gayet 1993; T. Grande 1994, 1996; T. Grande and Poyato-Ariza 1995, 1999; Poyato-Ariza 1996b; G. D. Johnson and Patterson 1997; Poyato-Ariza et al. 2010; Amaral and Brito 2012; Amaral et al. 2013; Ribeiro, Poyato-Ariza, et al. 2018). A diversity of molecular phylogenetic analyses of mtDNA, Sanger-sequenced nuclear genes, and phylogenomic datasets resolve Gonorynchus as the sister lineage of all other Gonorynchiformes (Lavoué et al. 2005; Lavoué, Miya, Moritz, et al. 2012; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; Davis et al. 2013; Chakrabarty et al. 2017; Straube et al. 2018). Morphological and molecular phylogenetic analyses consistently support Phractolaemus ansorgii and all other species of Kneriidae as sister taxa (T. Grande 1994; G. D. Johnson and Patterson 1997; T. Grande and Poyato-Ariza 1999; Lavoué et al. 2005; Lavoué, Miya, Moritz, et al. 2012; Davis et al. 2013; Near, Dornburg, and Friedman 2014). Relationships among the five living species of Gonorynchus were resolved in a phylogenetic analysis of 12 morphological characters (T. Grande 1999).

  • Composition. Gonorynchiformes currently contains 40 living species (Fricke et al. 2023; Kalumba et al. 2023) that include Chanos chanos and species classified in Gonorynchus and Kneriidae (T. Grande and Poyato-Ariza 1999). Fossil lineages of Gonorynchiformes include the pan-chanids †Aethalionopsis, †Dastilbe, †Gordichthys, †Parachanos, †Rubiesichthys, and †Tharrhias (Poyato-Ariza 1994, 1996a; Fara et al. 2010). Fossil pan-gonorynchid lineages include †Charitopsis, †Charitosomus, †Hakeliosomus, †Judeichthys, †Notogoneus, and †Ramallichthys (L. Grande and Grande 1999; Fara et al. 2010). Details of the ages and locations of the fossil taxa are given in Appendix 1. One new living species of Gonorynchiformes has been described over the past 10 years, comprising 2.6% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Gonorynchiformes include (1) bone and cartilage of interorbital septum reduced where orbitosphenoid absent (Fink and Fink 1981, 1996; Patterson 1984b; T. Grande and Poyato-Ariza 1995; Poyato-Ariza et al. 2010; Wiley and Johnson 2010), (2) parietals reduced in size to canal-bearing ossicles (Rosen and Greenwood 1970; Fink and Fink 1981; Patterson 1984b; Poyato-Ariza et al. 2010; Wiley and Johnson 2010), (3) middle region of suspensorium, bounded by articular condyle for quadrate and hyomandibular, longer relative to height of suspensorium and opercular series (Fink and Fink 1981, 1996; Wiley and Johnson 2010), (4) premaxilla thin and flat (Fink and Fink 1981, 1996; Patterson 1984b), (5) presence of bilateral pouches in branchial chamber located posterior to fourth epibranchial (Greenwood et al. 1966; Fink and Fink 1981, 1996; Wiley and Johnson 2010), (6) absence of teeth on fifth ceratobranchial (Fink and Fink 1981, 1996; Patterson 1984b; T. Grande and Poyato-Ariza 1999; Poyato-Ariza et al. 2010; Wiley and Johnson 2010), (7) anterior neural arch large, forming tight joint with exoccipital or exoccipital and supraoccipital (Fink and Fink 1981, 1996; Patterson 1984b; T. Grande and Poyato-Ariza 1999; Poyato-Ariza et al. 2010; Wiley and Johnson 2010), (8) presence of epicentral bones, also referred to as cephalic ribs (Patterson and Johnson 1995; Fink and Fink 1996; T. Grande and Poyato-Ariza 1999; Wiley and Johnson 2010), (9) absence of Baudelot's ligament (Patterson and Johnson 1995; Fink and Fink 1996; Wiley and Johnson 2010), (10) presence of exceptionally long esophagus (Fink and Fink 1996; Wiley and Johnson 2010), (11) pterosphenoids either slightly reduced, not articulating anteroventrally but in close proximity anterodorsally or greatly reduced and well-separated both anteroventrally and anterodorsally (T. Grande and Poyato-Ariza 1999; Poyato-Ariza et al. 2010), (12) parietals partially or completely separated by supraoccipital (T. Grande and Poyato-Ariza 1999; Poyato-Ariza et al. 2010), (13) ascending process of premaxilla absent (T. Grande and Poyato-Ariza 1999; Poyato-Ariza et al. 2010), (14) maximum height of dentary at midpoint or at anterior region close to symphysis (T. Grande and Poyato-Ariza 1999), (15) fewer than five infraorbitals (T. Grande and Poyato-Ariza 1999), (16) anterior neural arches slightly in contact with adjacent arches or exhibit overlapping lateral contact with adjacent arches (T. Grande and Poyato-Ariza 1999), (17) rib on third vertebral centrum wider and shorter than posterior ribs (T. Grande and Poyato-Ariza 1999; Poyato-Ariza et al. 2010), and (18) premaxilla, maxilla, and dentary without teeth (Poyato-Ariza et al. 2010).

  • Synonyms. Gonorhynchoidei (Gosline 1960:357, 1971:113–114), Anotophysi (Rosen and Greenwood 1970:23), and Anotophysa (Betancur-R et al. 2017:15) are ambiguous synonyms of Gonorynchiformes.

  • Comments. Gosline (1960, 1971:113–114) was the first investigator to delimit a group containing Gonorynchus, Chanos chanos, Cromeria, Kneria, and Phractolaemus ansorgii, which he named Gonorhynchoidei (sic). Greenwood et al. (1966) included the kneriid Grasseichthys gabonensis and named the group Gonorynchiformes. The name Gonorynchiformes was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade.

  • The earliest fossil Gonorynchiformes is the pan-chanid †Rubiesichthys gregalis from the Berriasian and Valanginian (143.1–132.6 Ma) in the Cretaceous of Spain (Poyato-Ariza 1996a). Bayesian relaxed molecular clock analyses of Gonorynchiformes using fossil tip-dating result in an average posterior crown age estimate of 219.8 million years ago, with the credible interval ranging between 201.7 and 240.0 million years ago (Near, Dornburg, and Friedman 2014).

  • img-z52-6_03.gif

    Otophysi W. Garstang 1931:253, 256
    [Lundberg 2020]

  • Definition. Defined as a minimum-crown-clade in Lundberg (2020a) as: “The crown clade originating in the most recent common ancestor of Cyprinus carpio Linnaeus 1758 (Cypriniformes), Charax (originally Salmo) gibbosus (Linnaeus 1758) (Characiformes), Gymnotus carpio Linnaeus 1758 (Gymnotiformes; Gymnotoidei on the reference phylogeny), and Silurus glanis Linnaeus 1758 (Siluriformes; Siluroidei on the reference phylogeny).”

  • Etymology. From the ancient Greek γτός (hˈo͡Ʊtˈo͡Ʊz), meaning belonging to the ear, and ϕῦσα (fˈuːsә), meaning bladder.

  • Registration number. 197.

  • Reference phylogeny. Fink and Fink (1981, fig. 1) was designated as the primary reference phylogeny by Lundberg (2020a). Phylogenetic relationships of the major lineages of Otophysi are presented in Figure 8. The placements of the pan-siluriform †Andinichthyidae and the pan-citharinid †Eocitharinus in the phylogeny are based on inferences from morphology (Arratia and Gayet 1995; Gayet and Meunier 2003; Murray 2003; Guinot and Cavin 2018).

  • Phylogenetics. Phylogenetic analyses of morphological characters resolve Otophysi as monophyletic and place Cypriniformes as the sister group of a clade containing Characiformes (sensu lato), Siluriformes, and Gymnotiformes (Fink and Fink 1981, 1996; Arratia 1992; Diogo et al. 2008). The monophyly of Otophysi is consistently supported by molecular phylogenetic studies, including analyses of whole mitochondrial genomes (Lavoué et al. 2005; Jondeung et al. 2007; Poulsen et al. 2009; Nakatani et al. 2011), collections of Sanger-sequenced mitochondrial or nuclear genes (Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; W.-J. Chen et al. 2013), and phylogenomic datasets (Arcila et al. 2017; Chakrabarty et al. 2017; Dai et al. 2018; Hughes et al. 2018; Straube et al. 2018; Faircloth et al. 2020). Within Otophysi, morphological and molecular phylogenies are incongruent with regards to the relationships of Characiformes (sensu lato), Siluriformes, and Gymnotiformes. Specifically, the traditional delimitation of Characiformes that includes Cithariniformes is not resolved as monophyletic relative to Siluriformes or Gymnotiformes in phylogenetic studies ranging from the early single locus analyses in the mid-1990s to phylogenomic analyses in the early 21st century (Ortí and Meyer 1996, 1997; Nakatani et al. 2011; Betancur-R, Broughton, et al. 2013; W.-J. Chen et al. 2013; Chakrabarty et al. 2017; Dai et al. 2018; Hughes et al. 2018, fig. S2; Faircloth et al. 2020; Simion et al. 2020; Melo, Sidlauskas, et al. 2022; Yang et al. 2023).

  • Composition. Otophysi currently contains more than 11,640 species (Fricke et al. 2023) classified in Characiformes, Cithariniformes, Cypriniformes, Gymnotiformes, and Siluriformes. Fossil otophysans include the Pan-Siluriformes lineage †Andinichthyidae (Gayet 1988a, 1990; Arratia and Gayet 1995; Gayet and Meunier 1998, 2003; Bogan et al. 2018) and the pan-cithariniform †Eocitharinus macrognathus (Murray 2003). Details of the ages and locations of the fossil taxa are presented in Appendix 1. Over the past 10 years there have been 1,683 new living species of Otophysi described (Fricke et al. 2023), comprising 14.5% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Otophysi include (1) axe-shaped endochondral portion of metapterygoid (Fink and Fink 1981, 1996; Wiley and Johnson 2010), (2) first or first and second anterior supraneurals with ventral expansion that forms synchondral joint with neural arches (Fink and Fink 1981, 1996; Wiley and Johnson 2010), (3) scaphium and claustrum of Weberian apparatus present (Fink and Fink 1981, 1996; Wiley and Johnson 2010), (4) reduction of second neural arch that is modified into intercalarium (Fink and Fink 1981, 1996; Wiley and Johnson 2010), (5) centra of anterior vertebrae shortened (Fink and Fink 1981, 1996; Wiley and Johnson 2010), (6) fusion of first two parapophyses and centra (Fink and Fink 1981, 1996; Wiley and Johnson 2010), (7) presence of the tripus, a bone that is an element of the Weberian apparatus and is likely a modified pleural rib (Fink and Fink 1981, 1996; Wiley and Johnson 2010), (8) presence of the os suspensorium (Fink and Fink 1981, 1996; Wiley and Johnson 2010), (9) pelvic bone bifurcated (Fink and Fink 1981, 1996; Wiley and Johnson 2010), (10) presence of compound terminal vertebrae (Fink and Fink 1981, 1996; Wiley and Johnson 2010), (11) hypural 2 fused with compound centrum (Fink and Fink 1981, 1996; Wiley and Johnson 2010), (12) the sinus impar of inner ear present (Fink and Fink 1981, 1996; Wiley and Johnson 2010), (13) loss of supradorsal 2 and all supradorsals posterior to vertebra 4 (Hoffmann and Britz 2006; Wiley and Johnson 2010), and (14) fusion of supradorsals 3 and 4 with supraneural 2 and 3 cartilages to form neural complex (Hoffmann and Britz 2006; Wiley and Johnson 2010).

  • Synonyms. Ostariophysen (Sagemehl 1885:22), Ostariophysi (Boulenger 1904b:573–596; Goodrich 1909:371; Regan 1911d:13–15, 1911e:554; Jordan 1923:134–153; Greenwood et al. 1966:380–382, 395–396; Gosline 1971:120–124), and Plectospondyli (Cope 1871a:454; Jordan 1923:134–153) are approximate synonyms of Otophysi. Cypriniformes is an ambiguous synonym of Otophysi (Bertin and Arambourg 1958:2285–2287; McAllister 1968:67–78).

  • Comments. Garstang (1931) delimited a more inclusive Otophysi that in addition to Siluriformes and Characiformes included Osteoglossiformes, Elopiformes, and Clupeiformes. Sagemehl (1885) applied the name Ostariophysen to a group now delimited as Otophysi. Rosen and Greenwood (1970) expanded Ostariophysi to include Gonorynchiformes, and placed Cypriniformes, Gymnotiformes, Siluriformes, and Characiformes (sensu lato) in Otophysi. The name Otophysi was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade.

  • Bayesian relaxed molecular clock analyses of Otophysi result in an average posterior crown age estimate of 146.9 million years ago, with the credible interval ranging between 137.9 and 156.5 million years ago (Hughes et al. 2018).

  • img-z54-4_03.gif

    Cypriniformes E. S. Goodrich 1909:371
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Catostomus catostomus (Forster 1773), Gyrinocheilus pustulosus Vaillant 1902, Cobitis taenia Linnaeus 1758, Cyprinus carpio Linnaeus 1758, and Paedocypris progenetica Kottelat et al. 2006. This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek κυπρῖνoς (kuːpɹˈ̍iːno͡Ʊz), frequently applied to the European Carp, Cyprinus carpio (D. W. Thompson 1947:135–136). The suffix is from the Latin forma, meaning form, figure, or appearance.

  • Registration number. 904.

  • Reference phylogeny. A phylogeny of 1,703 species of Cypriniformes inferred from a supermatrix of 27 nuclear and mitochondrial genes (Rabosky et al. 2018; J. Chang et al. 2019). The phylogeny is available on the Dryad data repository (Rabosky et al. 2019). Although the reference phylogeny does not include Paedocypris progenetica, the species resolves within the cyprinoid clade Danionidae (danionins) in phylogenetic analysis of mtDNA, combined mtDNA and nuclear gene sequences, and morphological characters (Rüber et al. 2007; Fang et al. 2009; K. L. Tang et al. 2010; Britz, Conway, et al. 2014). Phylogenetic analysis of DNA sequences of nuclear genes resolves Paedocypris as the sister lineage of Cyprinoidei or Cypriniformes (Mayden and Chen 2010; Stout et al. 2016; Malmstrøm et al. 2018). Phylogenetic relationships of living and fossil lineages of Cypriniformes are shown in Figure 9. The resolution of †Jianghanichthys in the phylogeny is based on analysis of morphological characters (J. Liu et al. 2015).

  • Phylogenetics. Greenwood et al. (1966) argued for monophyly of Cypriniformes on the basis of morphological characters from the pharyngeals, skull, oral jaws, vertebrae, and Weberian apparatus. X.-W. Wu et al. (1981) mapped morphological character changes onto a phylogeny that included Cyprinoidei and the cobitoid subclade Balitoridae (hillstream loaches) as sister lineages, a relationship that is not supported in any subsequent study of cypriniform phylogeny. Analysis of discretely coded morphological characters consistently resolves Cyprinoidei as the sister lineage of a clade containing Gyrinocheilus (algae eaters), Catostomidae (suckers), and Cobitoidei (Siebert 1987; Conway and Mayden 2007; Conway 2011). Inferred relationships differ among morphological analyses, with Gyrinocheilus and Catostomidae as successive sister lineages to Cobitoidei (Siebert 1987; Conway and Mayden 2007) or Gyrinocheilus and Catostomidae resolved as a clade that is the sister lineage of Cobitoidei (Conway 2011; Mabee et al. 2011; Britz, Conway, et al. 2014). Morphological phylogenetic analyses that include the Eocene-aged †Jianghanichthys result in a set of 116 most parsimonious trees. The strict consensus of these trees resolves the most recent common ancestor of Cypriniformes as a polytomy subtending Gyrinocheilus, Catostomidae, Cobitoidei, Cyprinoidei, and †Jianghanichthys (J. Liu et al. 2015).

  • The monophyly of Cypriniformes is supported in a range of molecular phylogenetic studies that include analyses of whole mitochondrial genomes (Saitoh et al. 2006, 2011; Jondeung et al. 2007; He, Gu, et al. 2008; Poulsen et al. 2009; Nakatani et al. 2011), trees inferred from collections of Sanger-sequenced mitochondrial or nuclear genes (Mayden et al. 2008, 2009; Mayden and Chen 2010; Betancur-R et al. 2017; Hirt et al. 2017; Luo et al. 2023), and analysis of phylogenomic datasets (Stout et al. 2016; Hughes et al. 2018). Molecular phylogenetic analyses uniformly resolve Catostomidae, Cobitoidei, Cyprinoidei, and Gyrinocheilus as monophyletic (Šlechtová et al. 2007; W.-J. Chen et al. 2009; Mayden and Chen 2010; Stout et al. 2016; Hirt et al. 2017; Tao et al. 2019); however, molecular analyses result in five different hypotheses of relationships among these four lineages (Saitoh et al. 2006; Šlechtová et al. 2007; W.-J. Chen et al. 2008; Mayden et al. 2008; Bohlen and Šlechtová 2009; Mayden and Chen 2010; Stout et al. 2016; Hirt et al. 2017; Tao et al. 2019).

  • Composition. Cypriniformes currently contains 4,827 living species (Fricke et al. 2023) classified in Catostomidae, Cobitoidei, Cyprinoidei, and Gyrinocheilus (Mayden and Chen 2010; Conway 2011; Tan and Armbruster 2018). †Jianghanichthys is the only fossil taxon of Cypriniformes that is not a lineage of Catostomidae, Cobitoidei, or Cyprinoidei (J. Liu et al. 2015). The age and location of †Jianghanichthys is presented in Appendix 1. Over the past 10 years 661 new living species of Cypriniformes have been described (Fricke et al. 2023), comprising 13.7% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Cypriniformes include (1) kinethmoid present (Fink and Fink 1981, 1996; Conway et al. 2010; Wiley and Johnson 2010; Conway 2011), (2) preethmoid present (Fink and Fink 1981, 1996; Conway et al. 2010; Wiley and Johnson 2010; Conway 2011), (3) dorsomedial autopalatine process present (Fink and Fink 1981, 1996; Conway et al. 2010; Wiley and Johnson 2010), (4) autopalatime-endopterygoid articulation present (Fink and Fink 1981, 1996; Conway et al. 2010; Wiley and Johnson 2010; Conway 2011), (5) loss of ectopterygoid-autopalatine overlap (Fink and Fink 1981, 1996; Conway et al. 2010; Wiley and Johnson 2010), (6) premaxilla extends furthest dorsally adjacent to midline (Fink and Fink 1981, 1996; Conway et al. 2010; Wiley and Johnson 2010; Conway 2011), (7) presence of ankylosed teeth on ceratobranchial 5 (Fink and Fink 1981, 1996; Conway et al. 2010; Wiley and Johnson 2010; Conway 2011), (8) lateral process of second vertebral centrum is elongate and projects into somatic musculature (Fink and Fink 1981, 1996; Conway et al. 2010; Wiley and Johnson 2010; Conway 2011), (9) absence of pharyngobranchial uncinate processes (Siebert 1987; Conway 2011), (10) three branchiostegal rays (Conway et al. 2010; Conway 2011; Mabee et al. 2011), and (11) teeth on ceratobranchial 5 arranged in a single row (Mabee et al. 2011).

  • Synonyms. Eventognathi (T. N. Gill 1861a:8–9; Gregory 1907:477–478; Jordan 1923:139–145), Cyprinidae (Boulenger 1904b:581–586; Goodrich 1909:375–376), Cyprinoidei (Berg 1940:444–446; Greenwood et al. 1966:384–386, 396; X.-W. Wu et al. 1981:572), Cyprinoidea (McAllister 1968:70–71), Cyprinoidae (Gosline 1971:121), and Cypriniphysae (Betancur-R et al. 2017) are ambiguous synonyms of Cypriniformes.

  • Comments. The taxa delimited here as Cypriniformes were grouped together in several pre-phylogenetic classifications (T. N. Gill 1893; Boulenger 1904b:581–586; Gregory 1907:477–478; Goodrich 1909:375–376; Regan 1911d; Jordan 1923:139–145; Berg 1940). The name Cypriniformes was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade. Despite the strong support for cypriniform monophyly, relationships among the constituent lineages are not well-resolved, and there are disparate hypotheses on the phylogenetic placement of Paedocypris (Britz and Conway 2011; Britz, Conway, et al. 2014; Tan and Armbruster 2018).

  • The earliest fossil Cypriniformes is †Jianghanichthys hubeiensis from the early Eocene (56.0–47.8 Ma) of China (J. Liu et al. 2015). Bayesian relaxed molecular clock analyses of Cypriniformes result in an average posterior crown age estimate of 97.2 million years ago, with the credible interval ranging between 84.9 and 115.3 million years ago (Hughes et al. 2018).

  • img-z57-1_03.gif

    FIGURE 9.

    Phylogenetic relationships of the major living lineages and fossil taxa of Cypriniformes, Cobitoidei, and Cyprinoidei. Filled circles identify the common ancestor of clades, with formal names defined in the clade accounts. Open circles highlight clades with informal group names. Fossil lineages are indicated with a dagger (†). Details of the fossil taxa are presented in Appendix 1.

    img-z55-1_03.jpg

    Cobitoidei L. J. F. J. Fitzinger 1832:332
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Botia almorhae Gray 1831 and Cobitis taenia Linnaeus 1758. This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek κωβπτις (cobitis), which is an adjective of the gudgeon Gobio gobio (Linnaeus 1758), translating to “like a gudgeon” (D. W. Thompson 1947:139; Kottelat 2012).

  • Registration number. 905.

  • Reference phylogeny. A phylogeny of 1,703 species of Cypriniformes inferred from a supermatrix of 27 nuclear and mitochondrial genes (Rabosky et al. 2018; J. Chang et al. 2019). The phylogeny is available on the Dryad data repository (Rabosky et al. 2019). Phylogenetic relationships of the major lineages of Cobitoidei are presented in Figure 9.

  • Phylogenetics. Analysis of morphological characters results in the resolution of a clade containing Catostomidae, Cobitoidei, and Gyrinocheilus (Siebert 1987; Conway and Mayden 2007; Conway 2011; Britz, Conway, et al. 2014), which had been called Cobitidoidea (Siebert 1987) and Cobitoidea (Sawada 1982; Conway et al. 2010; Simons and Gidmark 2010; J. S. Nelson et al. 2016:186). Morphological and molecular phylogenetic analyses consistently resolve Cobitoidei as monophyletic (Siebert 1987; Saitoh et al. 2006; Q. Tang et al. 2006; Šlechtová et al. 2007; Mayden et al. 2008, 2009; Bohlen and Šlechtová 2009; W.-J. Chen et al. 2009; Mayden and Chen 2010; Conway 2011; Britz, Conway, et al. 2014; Stout et al. 2016; Rabosky et al. 2018; Luo et al. 2023), but some molecular analyses resolve Cobitoidea as paraphyletic (W.-J. Chen et al. 2009; Stout et al. 2016).

  • Phylogenetic inferences of relationships within Cobitoidei are broadly congruent between morphological and molecular studies (e.g., Saitoh et al. 2006; Šlechtová et al. 2007; W.-J. Chen et al. 2009; Conway 2011; Mabee et al. 2011; Tao et al. 2019) with Botiidae (bottid loaches) placed as the sister lineage of all other Cobitoidei and resolution of a clade containing Cobitidae (loaches), Balitoridae (hillstream loaches), and Nemacheilidae (stone loaches) (Q. Tang et al. 2006; Mayden et al. 2008; Bohlen and Šlechtová 2009; Mayden and Chen 2010; S. Liu et al. 2012; Stout et al. 2016; Luo et al. 2023). Molecular phylogenies place Barbucca (fire-eyed loaches) and Serpenticobitis (serpent loaches) in Balitoridae (Šlechtová et al. 2007; Bohlen and Šlechtová 2009; Rabosky et al. 2018), Ellopostoma (enigmatic loaches) as the sister lineage of Nemacheilidae, Balitoridae, or a clade containing Balitoridae and Nemacheilidae (Bohlen and Šlechtová 2009; W.-J. Chen et al. 2009; Rabosky et al. 2018; Luo et al. 2023), and Vaillantella (longfin loaches) as the sister lineage of the cobitoid clade that contains Cobitidae, Ellopostoma, Balitoridae, and Nemacheilidae (Q. Tang et al. 2006; Šlechtová et al. 2007; Bohlen and Šlechtová 2009; W.-J. Chen et al. 2009; S. Liu et al. 2012; Stout et al. 2016; Rabosky et al. 2018).

  • Composition. There are currently 1,361 species of Cobitoidei (Fricke et al. 2023) classified in Balitoridae, Botiidae, Cobitidae, Ellopostoma, Nemacheilidae, and Vaillantella (Šlechtová et al. 2007; Bohlen and Šlechtová 2009; W.-J. Chen et al. 2009; Tan and Armbruster 2018). Over the past 10 years there have been 266 new living species of Cobitoidei described (Fricke et al. 2023), comprising 19.5% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological synapomorphies for Cobitoidei include (1) presence of transversus ventralis V process on ceratobranchial 5 (Siebert 1987; Conway 2011), (2) presence of second preethmoid (Conway 2011), (3) anteriormost edge of orbitosphenoid contacts ethmoid complex (Conway 2011), (4) presence of preautopalatine (Conway 2011), (5) presence of cleithral-occipital ligament (Conway 2011), and (6) third and fourth lateral line ossifications much larger than other lateral line ossifications (Conway 2011).

  • Synonyms. Cobitidoidea (Siebert 1987:43) and Cobitoidea (Sawada 1982:212) are approximate synonyms of Cobitoidei.

  • Comments. Cobitoidei was the name applied to the paraphyletic group that included all non-cyprinoid cypriniforms to the exclusion of Catostomidae (Kottelat 2012). Given the uncertainty in the phylogenetic relationships among major lineages of Cypriniformes (Figure 9), we apply the group name Cobitoidei to all non-cyprinoid cypriniforms to the exclusion of Gyrinocheilus and Catostomidae.

  • Cobitoidei are frequently classified with Catostomidae and Gyrinocheilus (Siebert 1987; Conway et al. 2010; J. S. Nelson et al. 2016:186) or with Gyrinocheilus to the exclusion of Catostomidae (Kottelat 2012). Some classifications of ray-finned fishes include Barbuccidae, Gastromyzontidae, and Serpenticobitidae as taxonomic families of Cobitoidei (Kottelat 2012; J. S. Nelson et al. 2016:191–193; Betancur-R et al. 2017; Tan and Armbruster 2018). Along with many other researchers, we include Barbucca, Gastromyzontinae, and Serpenticobitis in Balitoridae (Q. Tang et al. 2006; Šlechtová et al. 2007; Bohlen and Šlechtová 2009; W.-J. Chen et al. 2009; S. Liu et al. 2012; Z. S. Randall and Page 2015; Tao et al. 2019). This inclusive delimitation of Balitoridae is both consistent with phylogenetic relationships and reduces the number of redundant group names in the classification of Cobitoidei, as both Barbuccidae and Serpenticobitidae contain a single genus and ranking these clades as equivalent to Gastromyzontidae and Balitoridae conveys no information about their phylogenetic relationships.

  • The cobitoid fossil record is sparse and limited to Asia and Europe (Conway et al. 2010). The earliest fossil cobitoids are †Cobitis longipectoralis from the late early Miocene (18 Ma) and †C. nanningensis from the early-middle Oligocene in China (G.-J. Chen et al. 2010, 2015). Relaxed molecular clock analyses estimate the age of Cobitoidei to be between 50 and 78 million years ago (Hughes et al. 2018).

  • img-z58-6_03.gif

    Cyprinoidei L. J. F. J. Fitzinger 1832:332
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Cyprinus carpio Linnaeus 1758, Danio rerio (Hamilton 1822), Leuciscus leuciscus (Cuvier 1816), and Paedocypris progenetica Kottelat et al. 2006. This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek κυπρῖνoς (kuːpɹ̍iːno͡Ʊz), frequently applied to the European Carp, Cyprinus carpio (D. W. Thompson 1947:135–136).

  • Registration number. 906.

  • Reference phylogeny. A phylogeny of 1,703 species of Cypriniformes inferred from a supermatrix of 27 nuclear and mitochondrial genes (Rabosky et al. 2018; J. Chang et al. 2019). The phylogeny is available on the Dryad data repository (Rabosky et al. 2019). Although the reference phylogeny does not include Paedocypris progenetica, the species resolves within the cyprinoid clade Danionidae (danionins) in phylogenetic analysis of mtDNA, combined mtDNA and nuclear gene sequences, and morphological characters (Rüber et al. 2007; Fang et al. 2009; K. L. Tang et al. 2010; Britz, Conway, et al. 2014). Phylogenetic analysis of DNA sequences of nuclear genes resolves Paedocypris as the sister lineage of Cyprinoidei or Cypriniformes (Mayden and Chen 2010; Stout et al. 2016; Malmstrøm et al. 2018). Phylogenetic relationships among the major clades of Cyprinoidei are presented in Figure 9.

  • Phylogenetics. Inference of the phylogenetics of Cyprinoidei is challenged by the high diversity of species in the clade; incongruent relationships of miniature species classified in Paedocypris, Sundadanio, and Fangfangia (Mayden and Chen 2010; Britz et al. 2011; Britz, Conway, et al. 2014); and phylogenetic resolution of the southeast Asian Tanichthys (cardinal minnows) and the European Tinca tinca (Tench) (Conway et al. 2010; Simons and Gidmark 2010; Tan and Armbruster 2018). Despite the remaining problems in the phylogeny of Cyprinoidei, incremental resolution of their relationships over the past 30 years has led to the elevation of 11 taxonomic families that were all classified as Cyprinidae (carps) for over 100 years (T. N. Gill 1872, 1893; Hensel 1970; W.-J. Chen and Mayden 2009; Tan and Armbruster 2018).

  • Phylogenetic analysis of Cyprinoidei using morphological characters resolves Cyprinidae as the sister lineage of all other cyprinoid lineages and Danionidae (dianions) as the sister lineage of a clade containing Acheilognathidae (bitterlings), Gobionidae (gudgeons), Leuciscidae (true minnows), and Xenocyprididae (Cavender and Coburn 1992; Conway 2011). In addition, Tinca tinca has uncertain resolution and Psilorhynchus (torrent minnows) is the sister lineage of all other Cyprinoidei (Cavender and Coburn 1992; Conway 2011). Analysis of a dataset that expands the character matrix from Conway (2011) resolves the cyprinoid miniature lineages Paedocypris and Sundadanio in a clade with Danionella (Britz, Conway, et al. 2014).

  • There are many molecular phylogenetic studies of Cyprinoidei that collectively include all known major lineages. The types of molecular data include whole mtDNA genomes (Saitoh et al. 2006; He, Gu, et al. 2008; Mayden et al. 2008; Chen et al. 2023; Hao et al. 2023), individual mtDNA or nuclear genes (e.g., Cunha et al. 2002; X. Z. Wang et al. 2007; He, Mayden, et al. 2008), combinations of mtDNA and nuclear genes (e.g., W.-J. Chen and Mayden 2009; Mayden and Chen 2010; Tao et al. 2019), and phylogenomic datasets (Stout et al. 2016; Hughes et al. 2018). Molecular phylogenies consistently nest Psilorhynchus within Cyprinoidei as the sister lineage of Cyprinidae (Šlechtová et al. 2007; He, Gu, et al. 2008; W.-J. Chen and Mayden 2009; Mayden and Chen 2010; K. L. Tang et al. 2013; Hirt et al. 2017; Rabosky et al. 2018; Tao et al. 2019), resolve a clade containing Acheilognathidae, Gobionidae, Leptobarbus, Leuciscidae, Sundadanio, Tanichthys, Tinca tinca, and Xenocyprididae (W.-J. Chen and Mayden 2009; Fang et al. 2009; Mayden and Chen 2010; K. L. Tang et al. 2013; Stout et al. 2016; Hirt et al. 2017; Rabosky et al. 2018), and a lineage that includes Acheilognathidae, Gobionidae, Leuciscidae, Tanichthys, Tinca tinca, and Xenocyprididae (Saitoh et al. 2006; Rüber et al. 2007; X. Z. Wang et al. 2007, 2012; W.-J. Chen et al. 2008; He, Mayden, et al. 2008; Mayden et al. 2008, 2009; W.-J. Chen and Mayden 2009; Fang et al. 2009; Mayden and Chen 2010; K. L. Tang et al. 2013; Tao et al. 2013, 2019; Stout et al. 2016; Hirt et al. 2017; Hughes et al. 2018; Rabosky et al. 2018; F. Chen et al. 2023; Hao et al. 2023). The relationships of Tinca tinca and Tanichthys vary among studies, with some resolving these two lineages as closely related (Fang et al. 2009; Mayden and Chen 2010; K. L. Tang et al. 2013) and sharing phylogenetic affinities with Leuciscidae (X. Z. Wang et al. 2007, 2012; Stout et al. 2016; Rabosky et al. 2018) or Xenocyprididae (Rüber et al. 2007; Tao et al. 2013; Hirt et al. 2017; Tao et al. 2019).

  • Phylogenetic analysis of mtDNA, combined mtDNA and nuclear gene sequences, and morphological characters resolve Paedocypris within the cyprinoid subclade Danionidae (Rüber et al. 2007; Fang et al. 2009; K. L. Tang et al. 2010, 2013; Britz, Conway, et al. 2014); however, analysis of nuclear gene datasets places this taxon as the sister lineage of Cyprinoidei or Cypriniformes (Mayden and Chen 2010; Stout et al. 2016; Malmstrøm et al. 2018). Gene trees inferred from each of the six loci examined by Mayden and Chen (2010) exhibit six different phylogenetic resolutions of Paedocypris: nested in Cyprinidae, the sister lineage of Cyprinidae, the sister lineage of Cypriniformes, the sister lineage of Catostomidae, the sister lineage of Gyrinocheilus, and nested within Danionidae (Britz, Conway, et al. 2014). It is possible that the disparate phylogenetic placements of Paedocypris among molecular datasets are the result of long branch attraction related to the dramatically reduced size of its genome (Britz, Conway, et al. 2014; Malmstrøm et al. 2018).

  • Composition. There are currently more than 3,375 living species of Cyprinoidei (Fricke et al. 2023) that includes Tinca tinca and species in Acheilognathidae, Cyprinidae, Danionidae, Gobionidae, Leptobarbus (sultan barbs), Leuciscidae, Paedocypris, Psilorhynchus, Sundadanio, Tanichthys, Tinca, and Xenocyprididae. Over the past 10 years 395 new living species of Cyprinoidei have been described (Fricke et al. 2023), comprising 11.7% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Cyprinoidei include (1) absence of uncinate process on epibranchials 1 and 2 (Siebert 1987; Cavender and Coburn 1992; Conway et al. 2010), (2) pharyngobranchial 1 absent (Siebert 1987; Cavender and Coburn 1992; Conway et al. 2010), (3) pharyngobranchial 3 overlaps pharyngobranchial 2 (Siebert 1987; Cavender and Coburn 1992; Conway et al. 2010), (4) presence of well-developed subtemporal fossae (Siebert 1987; Cavender and Coburn 1992; Conway et al. 2010), (5) anterior opening of trigeminal-facial chamber positioned between prootic and pterosphenoid, (6) loss of contact between infraorbital 5 and supraorbital (Cavender and Coburn 1992; Conway et al. 2010), and (7) presence of opercular canal (Cavender and Coburn 1992; Conway et al. 2010).

  • Synonyms. Cyprinidae (T. N. Gill 1872:18, 1893:132; Siebert 1987:43; Howes 1991b:8–17; Cavender and Coburn 1992:296–300; J. S. Nelson 2006:139–143; Simons and Gidmark 2010:419–425) and Cyprinoidea (Greenwood et al. 1966:396; Conway 2011, fig. 43; J. S. Nelson et al. 2016:181) are ambiguous synonyms of Cyprinoidei.

  • Comments. The lineages of Cyprinoidei were long classified as Cyprinidae and highlighted as one of the most species-rich taxonomic families of vertebrates (T. N. Gill 1872; Jordan 1923; Greenwood et al. 1966; Howes 1991b; J. S. Nelson et al. 2016:181); however, the disassembly of Cyprinidae sensu lato into 12 taxonomic families was the result of a desire to preserve the Linnaean taxonomic family rank of the monogeneric Psilorhynchidae (Hora 1925) that is phylogenetically nested within Cyprinoidei (W.-J. Chen and Mayden 2009; Tan and Armbruster 2018). The name Cyprinoidei was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade. While it is appropriate to view the changing classification of Cyprinoidei as an outcome of greater resolution of their phylogenetic relationships, the uncertainty as to the phylogeny of the miniature lineages Paedocypris, Sundadanio, and Fangfangia (Britz, Conway, et al. 2014) remains one of the most important issues in vertebrate phylogeny.

  • The earliest fossil taxon of Cyprinoidei is †Palaeogobio zhongyuanensis, classified in Gobionidae from the early middle Eocene (approximately 47 Ma) of China (Zhou 1990; M.-M. Chang and Chen 2008). An interesting set of cyprinoid fossils from the Sangkarewang Formation in Sumatra, Indonesia is classified in Cyprinidae and Danionidae; however, the age of the formation is only tentatively assigned to the middle Eocene (Murray 2019, 2020). Bayesian relaxed molecular clock analyses of the crown age of Cyprinoidei result in a credible interval ranging between 67 and 98 million years ago (Hirt et al. 2017).

  • img-z60-7_03.gif

    Gymnotiformes C. T. Regan 1911d:23
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Gymnotus carapo Linnaeus 1758, Gymnotus pantherinus (Steindachner 1908), Apteronotus albifrons (Linnaeus 1766), and Sternopygus macrurus (Bloch and Schneider 1801). This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek γυµνός (d͡Ʒ̍Imno͡Ʊz), meaning naked, and νῶτoν (n̍a͡Ʊtәn), meaning back. The suffix is from the Latin forma, meaning form, figure, or appearance.

  • Registration number. 907.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of 966 ultraconserved element (UCE) loci (Alda et al. 2019). Although Gymnotus carapo is not included in the reference phylogeny, it resolves in a clade with five other species of Gymnotus, including G. pantherinus, in a phylogenetic analysis of Sanger-sequenced mitochondrial and nuclear genes (Tagliacollo et al. 2016, figs. 2–4). Phylogenetic relationships among the major lineages of Gymnotiformes are presented in Figure 8.

  • Phylogenetics. There is substantial morphological evidence supporting the monophyly of Gymnotiformes, which is consistently corroborated in molecular phylogenetic analyses (e.g., Fink and Fink 1981, 1996; Nakatani et al. 2011; W.-J. Chen et al. 2013; Arcila et al. 2017). Phylogenetic relationships among the five major lineages of Gymnotiformes differ among analyses of morphological characters (Triques 1993; Gayet et al. 1994; Albert 2001), short Sanger-sequenced fragments of mtDNA genes (Alves-Gomes et al. 1995), combined analyses of morphology and DNA sequences of mtDNA and nuclear genes (Albert and Crampton 2005; Tagliacollo et al. 2016), and phylogenomic datasets (Arcila et al. 2017; Alda et al. 2019). The phylogenies differ as to the resolution of the sister lineage of all other Gymnotiformes: analyses of morphology and combined molecular and morphological datasets place Gymnotidae (nakedback knifefishes) as the sister lineage of all other Gymnotiformes (Albert 2001; Albert and Crampton 2005; Tagliacollo et al. 2016) and phylogenies inferred from alternative morphological datasets and phylogenomic datasets composed of exons and UCEs resolve Apteronotidae (ghost knifefishes) as the sister to all other Gymnotiformes (Triques 1993; Gayet et al. 1994; Arcila et al. 2017; Alda et al. 2019). Coalescent-based species tree analysis of UCE loci results in a phylogenetic tree in which lineages that produce a pulse-type electrical signal [Gymnotidae, Hypopomidae (bluntnose knifefishes), and Rhamphichthyidae (sand knifefishes)] are a monophyletic group that is the sister group of a clade comprising lineages that produce a wave-type electrical signal [Apteronotidae and Sternopygidae (glass knifefishes)] (Alda et al. 2019).

  • Morphological studies imply that Gymnotiformes and Siluriformes share a common ancestor relative to other major clades of Otophysi (Fink and Fink 1981, 1996); however, no unconstrained phylogenetic analysis of molecular data supports this relationship (Dimmick and Larson 1996; Ortí and Meyer 1996; Nakatani et al. 2011; Betancur-R, Broughton, et al. 2013; W.-J. Chen et al. 2013; Arcila et al. 2017; Chakrabarty et al. 2017; Hughes et al. 2018; Melo, Sidlauskas, et al. 2022). The phylogeny of Otophysi inferred from molecular data suggests that the passive electroreception and its associated specialized neural anatomy, cytology, and physiology in Gymnotiformes and Siluriformes has multiple evolutionary origins or multiple losses within the clade (Fink and Fink 1996; Albert et al. 1998).

  • Composition. There are currently 272 living species of Gymnotiformes (Fricke et al. 2023) classified in Apteronotidae, Gymnotidae, Hypopomidae, Rhamphichthyidae, and Sternopygidae (Ferraris et al. 2017). Over the past 10 years 68 new living species of Gymnotiformes have been described (Fricke et al. 2023), comprising 25% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Gymnotiformes include (1) absence of palatine ossification and palatine cartilage with flexure permitting mobility (Fink and Fink 1981; Albert 2001), (2) mesopterygoid with vertical strut that usually articulates with orbitosphenoid (Fink and Fink 1981), (3) claustrum of Weberian apparatus absent as a separate ossified element (Fink and Fink 1981; Albert 2001), (4) anterior and posterior parts of Baudelot's ligament attach to cleithrum (Fink and Fink 1981), (5) pelvic girdle and pelvic fin absent (Fink and Fink 1981; Albert 2001), (6) dorsal fin absent (Fink and Fink 1981; Albert 2001), (7) presence of elongate anal fin (Fink and Fink 1981; Albert 2001), (8) anal fin rays articulate directly with proximal radials and distal radials are reduced (Fink and Fink 1981; Albert 2001), (9) caudal skeleton reduced to single element and caudal fin reduced or absent (Mago-Leccia and Zaret 1978; Fink and Fink 1981; Albert 2001), (10) anus placed ventral or anterior to pectoral fin origin (Fink and Fink 1981; Albert 2001), (11) absence of maxillary teeth (Albert 2001), (12) articular surface of maxilla on stalk (Albert 2001), (13) levator posterior muscle not differentiated, (14) lateral margins of parasphenoid not extending to a horizontal with trigeminal foramen (Albert 2001), (15) dorsal telencephalic area with large dorsalis centralis and small dorsalis medialis (Albert 2001), (16) eye in adults covered by epidermis (Albert 2001), (17) Schreckstoff club cells and fright response absent (Albert 2001), (18) ampullary organs organized into rosettes (Albert 2001), (19) ectopterygoid absent (Albert 2001), (20) metapterygoid triangular in shape (Albert 2001), (21) sixth epibranchial with elongate ascending process, and (22) presence of electric organs composed of rows of modified elongate myofibrils (Albert 2001).

  • Synonyms. Gymnonoti (T. N. Gill 1872:18; Jordan 1923:138), Gymnotidae (Boulenger 1904b:579–581), Gymnotoidei (Goodrich 1909:376–377; Berg 1940:443–444; Greenwood et al. 1966:383–384; Fink and Fink 1981:303), Gymnotoidea (McAllister 1968:69; Rosen and Greenwood 1970:23), and Gymnotoidae (Gosline 1971:121) are ambiguous synonyms of Gymnotiformes.

  • Comments. The group name Gymnotiformes has long been applied to the clade as defined above (Regan 1911d; Mago-Leccia 1978; J. S. Nelson 1984:154–156; Fink and Fink 1996; Betancur-R et al. 2017) and was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade.

  • The fossil record of Gymnotiformes is limited to a handful of fragmentary fossils, including †Humboldtichthys kirschbaumi from the Miocene of Bolivia (Gayet et al. 1994; Gayet and Meunier 2000; Albert and Fink 2007). A morphological phylogenetic analysis places the holotype specimen of †H. kirschbaumi within Sternopygidae (Albert and Fink 2007). Bayesian relaxed molecular clock analyses of Gymnotiformes result in an average posterior crown age estimate of 62.4 million years ago, with the credible interval ranging between 46.0 and 81.6 million years ago (Hughes et al. 2018).

  • img-z62-5_03.gif

    Cithariniformes J. M. Mirande 2017:342
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Citharinus citharus (Geoffroy St. Hilaire 1809) and Distichodus mossambicusPeters1852.Thisisaminimum-crown-clade definition.

  • Etymology. From the ancient Greek κυθνρα (kIθ̍α͡ә), meaning harp or lute. The suffix is from the Latin forma, meaning form, figure, or appearance.

  • Registration number. 908.

  • Reference phylogeny. A phylogeny inferred from a maximum likelihood analysis of DNA sequences from two mtDNA genes and two nuclear genes (Arroyave et al. 2013, fig. 4). Phylogenetic relationships of Cithariniformes are shown in Figure 8.

  • Phylogenetics. Analyses of morphological and molecular characters consistently support the monophyly of Cithariniformes (Vari 1979; Ortí and Meyer 1997; Buckup 1998; Calcagnotto et al. 2005; Arroyave and Stiassny 2011; Arroyave et al. 2013; Arcila et al. 2017, 2018; Lavoué et al. 2017; Rabosky et al. 2018; Betancur-R. et al. 2019; Burns and Sidlauskas 2019; Melo, Sidlauskas, et al. 2022).

  • Composition. There are currently 117 species of Cithariniformes (Fricke et al. 2023) classified in Citharinidae (citharinids) and Distichodontidae (distichodontids). Over the past 10 years nine new living species of Cithariniformes have been described (Fricke et al. 2023), comprising 7.7% of the living species diversity in the clade.

  • Diagnostic apomorphies. Vari (1979) listed 14 morphological synapomorphies that support monophyly of Cithariniformes; however, eight of these character states are either ancestral within Otophysi or are secondarily derived in some lineages of Characiformes (Fink and Fink 1981). Morphological character states consistent with the monophyly of Cithariniformes include (1) second and third vertebrae with ventral elaborations and ventral expansion of os suspensorium (Vari 1979), (2) bicuspidate teeth (Vari 1979), (3) postcleithra 2 and 3 fused (Vari 1979), (4) hypurals 1 and 2 fused (Vari 1979), (5) absences of lateral wings on supraethmoid (Vari 1979), and (6) large and ventrally ovate third posttemporal fossa bordered by epioccipital and exoccipital (Vari 1979).

  • Synonyms. Citharinidae (Regan 1911d:21–22; J. S. Nelson 1994:142–143) and Citharinoidei (Buckup 1993:138; J. S. Nelson et al. 2016:194–195; Betancur-R et al. 2017:17) are ambiguous synonyms of Cithariniformes.

  • Comments. Cithariniformes was a group name applied to the clade containing Citharinidae and Distichodontidae (Mirande 2017, table 3), but long classified as a lineage of Characiformes (Vari 1979; Fink and Fink 1981, 1996; Buckup 1998; Betancur-R et al. 2017). Molecular phylogenetic analyses consistently resolve Characiformes, Siluriformes, and Gymnotiformes as a clade to the exclusion of Cithariniformes (Nakatani et al. 2011; Betancur-R, Broughton, et al. 2013; W.-J. Chen et al. 2013; Chakrabarty et al. 2017; Hughes et al. 2018, fig. S2; Faircloth et al. 2020; Melo, Sidlauskas, et al. 2022; Yang et al. 2023). It is unknown whether the seven morphological apomorphies identified by Fink and Fink (1981) supporting the hypothesis that Cithariniformes and Characiformes share common ancestry are present in a wider range of characiform taxa; their study did not include species of Acestrorhynchus (needlejaws), Gasteropelecidae (freshwater hatchetfishes), Iguanodectidae (tetras), Serrasalmidae (pacus), or Triportheidae (elongate hatchetfishes). The monophyly of both Cithariniformes and Characiformes is validated in phylogenetic analyses of morphological data matrices that use an explicit optimality criterion (Buckup 1998; de Pinna et al. 2018). However, the relationships of these two lineages relative to Siluriformes and Gymnotiformes have not been investigated using morphological phylogenetic analyses that seek a tree or set of trees with an optimal distribution of character state changes.

  • The earliest Cithariniformes fossil is a tooth identified as a species of Distichodus from the Lower Nawata formation at Lothagam, Kenya dated to approximately 7.5 million years ago (McDougall and Feibel 1999; K. M. Stewart 2001, 2003). Bayesian relaxed molecular clock analyses of Cithariniformes result in an average posterior crown age estimate of 119.7 million years ago, with the credible interval ranging between 93.2 and 149.3 million years ago (Melo, Sidlauskas, et al. 2022).

  • img-z63-6_03.gif

    Siluriformes O. P. Hay 1929:25
    [Lundberg 2020]

  • Definition. Defined as a minimum-crown-clade in Lundberg (2020d) as: “The crown clade originating in the most recent common ancestor of Loricaria cataphracta Linnaeus 1758 (Loricarioidei), Diplomystes (originally Silurus) chilensis (Molina 1782) (Diplomystidae), and Silurus glanis Linnaeus 1758 (Siluroidei).”

  • Etymology. From the ancient Greek σίλoυρoς (sIl̍Ʊ͡ o͡Ʊz), which is the name applied to several species of catfishes in Europe and Egypt, including the Wels Catfish, Silurus glanis (D. W. Thompson 1947:233–237). The suffix is from the Latin forma, meaning form, figure, or appearance.

  • Registration number. 199.

  • Reference phylogeny. Sullivan et al. (2006, figs. 1, 2) was designated as the primary reference phylogeny by Lundberg (2020d). Phylogeny of the living and fossil lineages of Siluriformes is presented in Figure 10. The placements of the fossil lineages †Bachmannia and †Hypsidoris are on the basis of inferences from morphology (L. Grande 1987; L. Grande and de Pinna 1998; Azpelicueta and Cione 2011).

  • Phylogenetics. There are several reviews on the phylogenetics of Siluriformes prior to the application of molecular data (de Pinna 1998; Diogo 2003, 2004; Teugels 2003). The monophyly of Siluriformes is supported in analyses of morphological characters (Fink and Fink 1981, 1996; Mo 1991; Arratia 1992; de Pinna 1993; Diogo 2004) and in all molecular phylogenetic studies, which includes analyses of whole mitochondrial genomes (Jondeung et al. 2007; Poulsen et al. 2009; Nakatani et al. 2011; Schedel et al. 2022; Duong et al. 2023), collections of Sanger-sequenced mitochondrial or nuclear genes (Betancur-R, Broughton, et al. 2013; W.-J. Chen et al. 2013), and phylogenomic datasets (Arcila et al. 2017; Chakrabarty et al. 2017; Hughes et al. 2018).

  • The first explicit phylogenetic studies of relationships within Siluriformes were morphological analyses aimed at determining the relationships among the Loricarioidei (Howes 1983; Schaefer 1990) and the relationships of the Eocene fossil taxon †Hypsidoris (L. Grande 1987; L. Grande and de Pinna 1998). More inclusive morphological phylogenetic studies aimed at including representatives of all the taxonomic families of Siluriformes place Diplomystidae (velvet catfishes) as the sister lineage of all other catfishes (Mo 1991; de Pinna 1993, 1998); support the monophyly of Loricarioidei; and do not resolve Siluroidei as monophyletic (Mo 1991; de Pinna 1993, 1998). A subsequent morphological analysis roots the phylogeny on Diplomystidae and resolves both Loricarioidei and Siluroidei as monophyletic (Diogo 2004, fig. 3.124); however, this study was critiqued on issues involving character state polarity and homology (Schaefer 2006). The Eocene fossil taxa †Bachmannia and †Hypsidoris are resolved as the sister lineages of Diplomystidae and Siluroidei, respectively (L. Grande 1987; L. Grande and de Pinna 1998; Azpelicueta and Cione 2011).

  • Molecular phylogenetic analyses of Siluriformes consistently resolve Loricarioidei as the sister lineage of a clade containing Diplomystidae and Siluroidei (Sullivan et al. 2006; Lundberg et al. 2007; Nakatani et al. 2011; W.-J. Chen et al. 2013; Kappas et al. 2016; Arcila et al. 2017; Rivera-Rivera and Montoya-Burgos 2017, 2018; Schedel et al. 2022). In molecular phylogenetic studies, the monophyly of Loricarioidei and Siluroidei are strongly supported (e.g., Sullivan et al. 2006; Nakatani et al. 2011; Arcila et al. 2017; Schedel et al. 2022). Molecular evolutionary rate heterogeneity among lineages is proposed as a mechanism for the incongruence between morphological and molecular phylogenies with regard to the placement of Loricarioidei in contrast to Diplomystidae as the sister lineage of all other Siluriformes (Rivera-Rivera and Montoya-Burgos 2018).

  • Composition. Siluriformes currently contains 4,188 species (Fricke et al. 2023) classified in Loricarioidei, Diplomystidae, and Siluroidei. Siluriformes includes the pan-diplomystid †Bachmannia and the pan-siluroid †Hypsidoris (L. Grande 1987; L. Grande and de Pinna 1998; Gayet and Meunier 2003; Azpelicueta and Cione 2011). Details of the ages and locations of the siluriform fossil taxa are presented in Appendix 1. Over the past 10 years 628 new living species of Siluriformes have been described (Fricke et al. 2023), comprising 15% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Siluriformes include (1) parietal bones absent (Fink and Fink 1981, 1996; Arratia 1992, 2003a; Wiley and Johnson 2010; Lundberg 2020d), (2) autopalatine bone separate from suspensorium (Fink and Fink 1981, 1996; Wiley and Johnson 2010; Lundberg 2020d), (3) ectopterygoid and endopterygoid reduced and not articulating with metapterygoid, quadrate, and hyomandibular (Fink and Fink 1981, 1996; Arratia 1992; Wiley and Johnson 2010; Lundberg 2020d), (4) metapterygoid anterodorsal to quadrate (Fink and Fink 1981, 1996; Arratia 1992; Wiley and Johnson 2010; Lundberg 2020d), (5) symplectic and posterior process of quadrate absent (Fink and Fink 1981, 1996; Arratia 2003a; Wiley and Johnson 2010; Lundberg 2020d), (6) preopercle and interopercle shortened (Fink and Fink 1981, 1996; Wiley and Johnson 2010; Lundberg 2020d), (7) subopercles absent (Fink and Fink 1981, 1996; Arratia 1992, 2003a; Wiley and Johnson 2010; Lundberg 2020d), (8) complex centrum formed by fusion of centra 2, 3, and 4 (Fink and Fink 1981, 1996; Arratia 1992; Wiley and Johnson 2010; Lundberg 2020d), (9) third and fourth neural arches fused to each other and to complex centrum (Fink and Fink 1981, 1996; Arratia 1992; Wiley and Johnson 2010; Lundberg 2020d), (10) parapophysis of second vertebral centrum absent (Fink and Fink 1981, 1996; Arratia 1992; Wiley and Johnson 2010; Lundberg 2020d), (11) transformator process of Weberian apparatus tripus separated posteriorly by width of the complex centrum (Fink and Fink 1981, 1996; Arratia 1992; Wiley and Johnson 2010), (12) parapophysis of fourth vertebral centrum expanded and articulating with posttemporal supracleithrum (Fink and Fink 1981, 1996; Arratia 1992; Wiley and Johnson 2010; Lundberg 2020d), (13) parapophysis of fourth vertebral centrum fused to complex centrum (Fink and Fink 1981, 1996; Arratia 1992; Wiley and Johnson 2010), (14) os suspensorium of Weberian apparatus consisting of only an anterior horizontal process (Fink and Fink 1981, 1996; Arratia 1992; Wiley and Johnson 2010), (15) suspensorium of pectoral girdle consisting of single ossified element including the supracleithrum, an ossified Baudelot's ligament, and posttemporal (Fink and Fink 1981, 1996; Arratia 1992; Wiley and Johnson 2010; Lundberg 2020d), (16) Baudelot's ligament distally bifurcated (Fink and Fink 1981, 1996), (17) dorsal fin with two tightly bound anterior spines (Lundberg et al. 2007; Lundberg 2020d), (18) skin naked with no bony-ridge scales that are present in most other lineages of Teleostei (Fink and Fink 1981, 1996; Lundberg 2020d), (19) palatoquadrate with separate pars autopalatine (Arratia 1992), (20) posterior palatoquadrate fused with symplectic cartilage (Arratia 1992), (21) articulation of autopalatine and vomer at midpoint of autopalatine (Arratia 1992), (22) articulation of autopalatine and lateral ethmoid at mid length of autopalatine (Arratia 1992), (23) entopterygoid not the main support for the eye (Arratia 1992), (24) retroarticular and anguloarticular fused (Arratia 1992), (25) Meckel cartilage with coronoid process (Arratia 1992), (26) upper pharyngeal tooth plate with retractor muscles (de Pinna 1993), (27) first pharyngobranchial lies parallel to first epibranchial (de Pinna 1993), (28) second pharyngobranchial elongated and rod-like (de Pinna 1993), (29) first basibranchial absent (de Pinna 1993), (30) intermuscular epineural and epipleural bones absent (Arratia 2003b; Lundberg 2020d), (31) maxillary bears a fleshy barbel (Lundberg 2020d), (32) basihyal absent (Lundberg 2020d), (33) postcleithra absent (Lundberg 2020d), and (34) pectoral fin with single spine with rotating and locking joint that articulates with cleithrum (Lundberg 2020d).

  • Synonyms. Siluridae (Swainson 1838:325–360; Günther 1864a:1–2), Siluri (Bleeker 1858:13–43), Nematognathi (T. N. Gill 1861a:11; Eigenmann and Eigenmann 1890:5; Jordan 1923:145–153), Siluroidei (Goodrich 1909:377–384; Bertin and Arambourg 1958:2302–2304; McAllister 1968:71–78), and Siluroidea (Regan 1911e) are ambiguous synonyms of Siluriformes.

  • Comments. The lineages delimited here as Siluriformes were grouped together in several pre-Darwinian and pre-cladistic classifications of teleosts (Bleeker 1858; Günther 1864a; Boulenger 1904b), with a degree of sophistication exemplified by placing Diplomystidae apart from all other groups of Siluriformes based on the presence of a toothed maxillary (Goodrich 1909:380; Regan 1911e). The monophyly of Siluriformes is consistently supported, from the first phylogenetic treatments of fishes to recent molecular analyses (Greenwood et al. 1966; Fink and Fink 1981; Nakatani et al. 2011; Arcila et al. 2017; Hughes et al. 2018). Remaining problems in the phylogenetics of Siluriformes include the incongruence among morphological and molecular studies regarding Diplomystidae or Loricarioidei as the sister lineage of all other Siluriformes (Mo 1991; de Pinna 1993; Arcila et al. 2017; Rivera-Rivera and Montoya-Burgos 2018) and the slight morphological support for the monophyly of Siluroidei (Diogo 2004; Lundberg et al. 2014).

  • The earliest fossils of Siluriformes that are not Loricarioidei or Siluroidei are Campanian (83.2–72.2 Ma) and Maastrichtian (72.2–66.0 Ma) pectoral spines identified as Diplomystidae from Argentina and Bolivia (Cione 1987; Arratia and Cione 1996; Gayet and Meunier 1998). Bayesian relaxed molecular clock analyses of Siluriformes result in an average posterior crown age estimate of 121.4 million years ago, with the credible interval ranging between 111.3 and 131.7 million years ago (Hughes et al. 2018).

  • img-z67-1_03.gif

    FIGURE 10.

    Phylogenetic relationships of the major living lineages and fossil taxa of Siluriformes, Loricarioidei, and Siluroidei. Filled circles identify the common ancestor of clades, with formal names defined in the clade accounts. Open circles highlight clades with informal group names. Fossil lineages are indicated with a dagger (†). Details of the fossil taxa are presented in Appendix 1.

    img-z64-1_03.jpg

    Loricarioidei P. Bleeker 1858:37
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Nematogenys inermis (Guichenot 1848), Loricaria cataphracta Linnaeus 1758, Loricaria simillima Regan 1904a, and Trichomycterus guianense (Eigenmann 1909). This is a minimum-crown-clade definition.

  • Etymology. From the Latin lorica, a coat of chain mail armor, in reference to the bony plates on the body of many species in this clade.

  • Registration number. 909.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of two nuclear genes (Sullivan et al. 2006, fig. 1). Although Loricaria cataphracta is not included in the reference phylogeny, it resolves with other species of Loricaria in molecular phylogenetic analyses (Covain et al. 2016, fig. 7; Moreira et al. 2017, fig. 3). Phylogenetic relationships among the major lineages of Loricarioidei are presented in Figure 10.

  • Phylogenetics. Morphological and molecular phylogenetic analyses consistently support the monophyly of Loricarioidei (Howes 1983; Schaefer 1990; Mo 1991; de Pinna 1993, 1998; Diogo 2004; Sullivan et al. 2006; Lundberg et al. 2007; Covain et al. 2016; Arcila et al. 2017; Moreira et al. 2017; Schedel et al. 2022). Within Loricarioidei, morphological and molecular analyses resolve two primary clades: Trichomycteridae (pencil catfishes) and Nematogenys inermis (Mountain Catfish) form a monophyletic group that is the sister lineage of a clade containing Callichthyidae (callichthyid armored catfishes), Astroblepus (climbing catfishes), and Loricariidae (sucker-mouth armored catfishes) (Mo 1991; de Pinna 1993, 1998; Arcila et al. 2017).

  • Composition. Loricarioidei currently contains 1,773 species (Ferraris 2007; Fricke et al. 2023) that includes Nematogenys inermis and species classified in Astroblepus, Callichthyidae, Loricariidae, Nematogenys, Scoloplax (spiny dwarf catfishes), and Trichomycteridae (Sullivan et al. 2006). There have been 391 new living species of Loricarioidei described over the past 10 years (Fricke et al. 2023), comprising 22.1% of the living species diversity of the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Loricarioidei include (1) odontodes present (Baskin 1973; Howes 1983; Schaefer and Lauder 1986; Schaefer 1990; de Pinna 1998), (2) encapsulated swim bladder present (Howes 1983; Schaefer and Lauder 1986; Schaefer 1990), (3) median processes of exoccipitals do not meet at midline (de Pinna 1998), (4) absence of anterior cartilages on arms of basipeterygium (de Pinna 1998), (5) bifid cusps on oral jaw teeth (de Pinna 1998), and (6) autopalatine compressed dorsoventrally with dorsal process that forms surface of articulation with neurocranium (Diogo 2004).

  • Synonyms. Loricarioidea (Schaefer and Lauder 1986, fig. 1; de Pinna 1998:292–294, fig. 6) is an ambiguous synonym of Loricarioidei.

  • Comments. On the basis of the results of morphological and molecular phylogenetic studies (e.g., Schaefer 1990; Sullivan et al. 2006), the group name Loricarioidei was applied to the clade containing Loricariidae, Astroblepus, Scoloplax, Callichthyidae, Trichomycteridae, and Nematogenys (Sullivan et al. 2006).

  • The earliest phylogenetic analyses within Siluriformes aimed to resolve relationships among lineages of Loricarioidei (Howes 1983; Schaefer 1990). The results of morphological and molecular phylogenetic analyses of relationships within Loricarioidei are broadly congruent (e.g., de Pinna 1993; Arcila et al. 2017).

  • The earliest fossil Loricarioidei is the callichthyid †Corydoras revelatus from the Late Paleocene (58.5 Ma) of Argentina (Marshall et al. 1997; Lundberg et al. 1998; Reis 1998). Relaxed molecular clock analyses estimate the crown age of Loricarioidei at approximately 90 million years ago (Rabosky et al. 2018).

  • img-z68-1_03.gif

    Siluroidei P. Bleeker 1858:34
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Silurus glanis Linnaeus 1758, Cetopsis coecutiens (Lichtenstein 1819), and Pimelodus maculatus Lacepède 1803, but not Loricaria simillima Regan 1904a or Diplomystes nahuelbutaensis Arratia 1987b. This is a minimum-crown-clade definition with external specifiers.

  • Etymology. From the ancient Greek σίλoυρoς (sIl̍Ʊɹo͡Ʊz), which is the name applied to several species of catfishes in Europe and Egypt, including the Wels Catfish, Silurus glanis (D. W. Thompson 1947:233–237).

  • Registration number. 910.

  • Reference phylogeny. A phylogeny of 752 species of Siluroidei inferred from a supermatrix of 27 nuclear and mitochondrial genes (Rabosky et al. 2018; J. Chang et al. 2019). The phylogeny is available on the Dryad data repository (Rabosky et al. 2019). Phylogenetic relationships among the major lineages of Siluroidei are presented in Figure 10.

  • Phylogenetics. The first phylogenetic studies to resolve Siluroidei as monophyletic include analyses of 440 morphological characters and DNA sequences of two nuclear genes (Diogo 2004, fig. 3.124; Sullivan et al. 2006). Molecular phylogenetic analyses consistently support the monophyly of Siluroidei; however, relationships among deeper nodes are typically unresolved and poorly supported (Sullivan et al. 2006; Lundberg et al. 2007; Kappas et al. 2016; Arcila et al. 2017; Rivera-Rivera and Montoya-Burgos 2018; K. Zhang, Liu, et al. 2021; Schedel et al. 2022; Duong et al. 2023). Despite the lack of strong resolution along the backbone of the siluroid phylogeny, there are several well-supported conclusions from morphological and molecular phylogenetic analyses. For example, Cetopsidae (whale catfishes) are either deeply branching or specifically placed as the sister lineage of all other Siluroidei in many phylogenetic studies (Mo 1991; de Pinna 1993; Diogo 2004; Lundberg et al. 2007; Q. Wang et al. 2015; Arcila et al. 2017; Rivera-Rivera and Montoya-Burgos 2018; K. Zhang, Liu, et al. 2021; Schedel et al. 2022; Duong et al. 2023). Phylogenies inferred from both morphological and molecular datasets result in the polyphyly of the traditional delimitation of Schilbeidae (butter catfishes) distributed in freshwater habitats of Africa and Asia (Mo 1991; de Pinna 1993; Hardman 2005; Sullivan et al. 2006; Schedel et al. 2022), with Asian lineages subsequently classified in Ailiidae (Asian schilbeids) (J. Wang et al. 2016; X. Li and Zhou 2018). Phylogenetic analyses consistently support the common ancestry of several groupings of siluroid lineages: Aspredinidae (banjo catfishes), Auchenipteridae (driftwood catfishes), and Doradidae (thorny catfishes) (Sullivan et al. 2006, 2008; Nakatani et al. 2011; Q. Wang et al. 2015; Arcila et al. 2017; Rabosky et al. 2018; Rivera-Rivera and Montoya-Burgos 2018; Cui et al. 2020; K. Zhang, Liu,et al. 2021; Schedel et al. 2022; Duong et al. 2023); Clariidae (airbreathing catfishes) and Heteropneustes (airsac catfishes) (Mo 1991; Diogo 2004; Hardman 2005; Sullivan et al. 2006; Nakatani et al. 2011; Q. Wang et al. 2015; J. Wang et al. 2016; Rabosky et al. 2018; Cui et al. 2020; K. Zhang, Liu, et al. 2021; Schedel et al. 2022; Duong et al. 2023); the Madagascar endemic Anchariidae (Malagasy catfishes) and the marine Ariidae (sea catfishes) (de Pinna 1993; Sullivan et al. 2006; J. Wang et al. 2016); and the east Asian Cranoglanis (armorhead catfishes) and the North American Ictaluridae (bullhead catfishes) (Diogo 2004; Hardman 2005; Sullivan et al. 2006; Nakatani et al. 2011; Q. Wang et al. 2015; Kappas et al. 2016; J. Wang et al. 2016; Rabosky et al. 2018; Cui et al. 2020; Schedel et al. 2022; Duong et al. 2023).

  • An important result from the earliest inclusive molecular phylogenetic analyses of Siluroidei was the resolution of two inclusive clades: Big Asia [Ailiidae, Akysidae (stream catfishes), Amblycipitidae (torrent catfishes), Bagridae (bagrid catfishes), Horabagridae (sun catfishes), and Sisoridae (sisorid catfishes)] and Big Africa [Amphiliidae (loach catfishes), Claroteidae (claroteids), Lacantunia enigmatica (Chiapas Catfish), Malapteruridae (electric catfishes), Mochokidae (squeakers), and Schilbeidae], which highlighted freshwater habitats in Asia and Africa as important areas of siluroid diversification (Sullivan et al. 2006; Lundberg et al. 2007). Molecular phylogenetic analyses resolve the enigmatic Conorhynchos conirostris (Anteater Catfish), which is currently not classified in a Linnean-ranked taxonomic family (Eschmeyer and Fricke 2023), in a clade with other South American freshwater lineages that includes Heptapteridae (threebarbeled catfishes), Pimelodidae (long-whiskered catfishes), and Pseudopimelodidae (bumblebee catfishes) (Sullivan et al. 2006, 2013; G. S. C. Silva et al. 2021). An analysis of a supermatrix of 27 nuclear and mitochondrial genes places this South American siluroid lineage in the Big Africa clade (Rabosky et al. 2018; J. Chang et al. 2019).

  • Morphological and molecular studies provide insight into the phylogenetic relationships of the enigmatic South African lineage Austroglanis (rock catfishes) and two species discovered and described in the early 21st century, Lacantunia enigmatica and Kryptoglanis shajii (Subterranean Catfish) (Skelton et al. 1984; Rodiles-Hernández et al. 2005; Vincent and Thomas 2011; Britz, Kakkassery, et al. 2014). Austroglanis was initially classified in Bagridae (Skelton et al. 1984), but morphological and molecular analyses place this lineage in a clade that contains Cranoglanis, Ictaluridae, and Anchariidae or as the sister lineage of Pangasiidae (Diogo 2004; Rabosky et al. 2018; Schedel et al. 2022). Lacantunia enigmatica was discovered in the Rio Usumacinta basin in Chiapas, Mexico and Kryptoglanis shajii was discovered from subterranean waters in Kerala, India (Rodiles-Hernández et al. 2005; Vincent and Thomas 2011). Both species were each classified in monotypic taxonomic families, Lacantuniidae and Kryptoglanidae (Rodiles-Hernández et al. 2005; Britz, Kakkassery, et al. 2014). Molecular analyses resolve L. enigmatica and the African freshwater Claroteidae as sister lineages (Lundberg et al. 2007; Rabosky et al. 2018). Morphological characters suggest K. shajii is closely related to Siluridae (Lundberg et al. 2014).

  • Composition. There are currently 2,408 living species of Siluroidei (Ferraris 2007; Fricke et al. 2023) that includes Conorhynchos conirostris, Kryptoglanis shajii, Lacantunia enigmatica, Rita (ritas), and species classified in Ailiidae, Akysidae, Amblycipitidae, Amphiliidae, Anchariidae, Ariidae, Aspredinidae, Auchenipteridae, Auchenoglanididae (auchenoglanids), Austroglanis, Bagridae, Cetopsidae, Chaca (squarehead catfishes), Clariidae, Claroteidae, Cranoglanis, Doradidae, Heptapteridae, Heteropneustes, Horabagridae, Ictaluridae, Malapteruridae, Mochokidae, Pangasiidae (shark catfishes), Phreatobius (underground catfishes), Pimelodidae, Plotosidae (eeltail catfishes), Pseudopimelodidae, Schilbeidae, Siluridae, and Sisoridae. Over the past 10 years 236 new living species of Siluroidei have been described (Fricke et al. 2023), comprising 9.8% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Siluroidei include (1) protractor hyoideus differentiated into pars dorsalis, ventralis, and lateralis (Diogo 2004), (2) articulatory surface of autopalatine for neurocranium directed mesially (Diogo 2004), (3) coronomeckelian bone reduced (Diogo 2004), (4) barbels located on anterior rim of posterior nostril (Lundberg et al. 2014), and (5) parasphenoid positioned along anterior margin of trigeminofacial foramen (Lundberg et al. 2014).

  • Synonyms. There are no synonyms of Siluroidei.

  • Comments. Siluriformes is a clade that was long recognized as a taxonomic group and its composition was unchanged in post-Darwinian and phylogenetic classifications, but Siluroidei is a subclade discovered as a result of phylogenetic analyses in the first 10 years of the 21st century (Diogo 2004; Sullivan et al. 2006). Work remains in resolving the phylogenetic relationships among the lineages of Siluroidei, with initial phylogenomic analyses showing considerable potential (Arcila et al. 2017).

  • The earliest fossils of Siluroidei are Campanian (83.2–72.2 Ma) and Maastrichtian (72.2–66.0 Ma) pectoral spines and fragments of skull bones of Ariidae in Argentina (Cione 1987; Arratia and Cione 1996; Gayet and Meunier 1998). Relaxed molecular clock analyses estimate the crown age of Siluroidei between 100 and 105 million years ago (Lundberg et al. 2007).

  • img-z70-2_03.gif

    Characiformes C. T. Regan 1911d:15
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Crenuchus spilurus Günther 1863a, Alestes inferus Stiassny, Schelly, and Mamonekene 2009, Charax gibbosus (Linnaeus 1758), and Charax metae Eigenmann 1922, but not Citharinus congicus Boulenger 1897. This is a minimum-crown-clade definition with an external specifier.

  • Etymology. From the ancient Greek χάραξ (k̍α͡ɹɹæks) as a name for species of Sparidae that exhibit teeth on the oral jaws (D. W. Thompson 1947:284–285). The suffix is from the Latin forma, meaning form, figure, or appearance.

  • Registration number. 911.

  • Reference phylogeny. A phylogeny of 293 species of Characiformes inferred from DNA sequences of 1,288 ultraconserved element (UCE) loci (Melo, Sidlauskas, et al. 2022, fig. 1). Although Charax gibbosus is not included in the reference phylogeny, it resolves in a clade with three other species of Charax in a phylogenetic analysis of morphological characters (Mattox and Toledo-Piza 2012, fig. 41). See Figure 11 for the phylogenetic relationships among the major lineages of Characiformes.

  • Phylogenetics. The first phylogenetic studies of Characiformes utilized morphological characters to investigate relationships among the subclades Curimatidae (toothless characiforms), Prochilodontidae (flannelmouth characiforms), Anostomidae (toothed headstanders) (Vari 1983), Ctenoluciidae (pike characids), Lebiasinidae (pencilfishes), Hepsetus (African pikes), and Erythrinidae (trahiras) (Vari 1995). Phylogenetic analyses of molecular and morphological matrices consistently support the monophyly of Characiformes relative to Cithariniformes and other otophysans (Ortí 1997; Ortí and Meyer 1997; Buckup 1998; Calcagnotto et al. 2005; Hubert et al. 2005a, 2005b; Mirande 2009; Oliveira et al. 2011; Arcila et al. 2017, 2018; de Pinna et al. 2018; Betancur-R. et al. 2019; Burns and Sidlauskas 2019; Melo, Sidlauskas, et al. 2022). There is extensive incongruence among phylogenetic analyses of Characiformes; the analysis of multiple morphological datasets results in different phylogenies (Buckup 1998; Mirande 2009), different trees are inferred from different molecular datasets (e.g., Ortí and Meyer 1997; Oliveira et al. 2011), and there are substantial differences between phylogenies inferred from morphological and molecular datasets (e.g., Vari 1995; Mirande 2009; Betancur-R. et al. 2019; Melo, Sidlauskas, et al. 2022). Two sets of relationships that are congruent between phylogenies inferred from morphological and molecular datasets are the resolution of the phenotypically unique Tarumania walkerae (Muck Fish) as the sister lineage of all other species of Erythrinidae (Arcila et al. 2018; de Pinna et al. 2018; Melo, de Pinna, et al. 2022) and the monophyly of Anostomoidea that contains Anostomidae, Chilodontidae (headstanders), Curimatidae, and Prochilodontidae (Vari 1983; Buckup 1998; Oliveira et al. 2011; Dillman et al. 2016; Arcila et al. 2017, 2018; Melo et al. 2018; Betancur-R. et al. 2019; Burns and Sidlauskas 2019; Melo, Sidlauskas, et al. 2022).

  • Molecular phylogenetic studies with dense taxon sampling using either collections of Sanger-sequenced mtDNA and nuclear genes or phylogenomic datasets exhibit adequate congruence to highlight several consistent results. Crenuchidae (South American darters) is the sister lineage of all other Characiformes (Oliveira et al. 2011; Arcila et al. 2017, 2018; Betancur-R. et al. 2019; Burns and Sidlauskas 2019; Melo, de Pinna, et al. 2022; Melo, Sidlauskas, et al. 2022). The lineage Chalceus (toucanfishes) was traditionally classified in Alestidae (African tetras) (Zanata and Vari 2005; Mirande 2009, 2010), but is resolved as the sister lineage of a clade containing Acestrorhynchidae (needlejaws), Bryconidae (South American trouts), Characidae (tetras), Gasteropelecidae (freshwater hatchetfishes), Iguanodectidae (tetras), and Triportheidae (elongate hatchetfishes) (Arroyave and Stiassny 2011; Oliveira et al. 2011; Arcila et al. 2017, 2018; Betancur-R. et al. 2019; Burns and Sidlauskas 2019; Melo, Sidlauskas, et al. 2022). The predatory lineages Ctenoluciidae and Hepsetidae are sister lineages in a morphological phylogeny (Buckup 1998); however, molecular phylogenies resolve a monophyletic group containing both African characiform lineages Hepsetidae and Alestidae (Oliveira et al. 2011; Arcila et al. 2017, 2018; Betancur-R. et al. 2019; Melo, de Pinna, et al. 2022; Melo, Sidlauskas, et al. 2022). The traditional delimitation of the species-rich Characidae (Lima et al. 2003; Mirande 2009, 2010) is not monophyletic in molecular phylogenies, prompting the elevation of Acestrorhynchidae, Bryconidae, Iguanodectidae, and Triportheidae; Characidae was restricted to species lacking a supraorbital (Lucena and Menezes 1998; Mirande 2009; Oliveira et al. 2011).

  • Composition. Characiformes currently contains 2,238 species (Fricke et al. 2023) classified in Acestrorhynchidae, Alestidae, Anostomidae, Bryconidae, Chalceus, Characidae, Chilodontidae, Crenuchidae, Ctenoluciidae, Curimatidae, Cynodontidae (dogtooth characins), Erythrinidae, Gasteropelecidae, Hemiodontidae, Hepsetus, Iguanodectidae, Lebiasinidae, Parodontidae (scrapetooths), Prochilodontidae, Serrasalmidae (pacus), and Triportheidae. Over the past 10 years 317 new living species of Characiformes have been described (Fricke et al. 2023), comprising 14.2% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological synapomorphies of Characiformes include (1) fourth neural arch fused to vertebra (Fink and Fink 1981; Buckup 1998), (2) synchondral joint between third and fourth neural arches reduced or absent (Fink and Fink 1981; Buckup 1998), (3) pelvic girdle slightly emarginate anteriorly (Fink and Fink 1981), (4) medial portion of joint between mesethmoid and vomer either flat or covered by midsagittal osseus or cartilaginous crest (Buckup 1998), and (5) A1 and A2 muscles of adductor mandibulae completely separated at their origins (Datovo and Castro 2012).

  • Synonyms. Heterognathi (T. N. Gill 1893:131; Jordan 1923:134–138), Characoidei (Greenwood et al. 1966:383–384), and Characoidea (McAllister 1968:69; Rosen and Greenwood 1970:23; T. R. Roberts 1973:377) are approximate synonyms of Characiformes. Characoidei (Buckup 1998, table 3; Betancur-R et al. 2017:17) is an ambiguous synonym of Characiformes.

  • Comments. As delimited here, Characiformes resolves as a monophyletic group in morphological and molecular phylogenetic analyses (e.g., Buckup 1998; Melo, Sidlauskas, et al. 2022). Characiformes and Cithariniformes were classified together in a more inclusive Characiformes from the mid-19th century to the present day (Günther 1864a; Betancur-R et al. 2017). Molecular phylogenetic analyses consistently fail to resolve Characiformes and Cithariniformes as a monophyletic group relative to other clades of Otophysi. The phylogenies of Characiformes inferred from phylogenomic datasets are not only resolving relationships among the most inclusive lineages in the clade (Arcila et al. 2017; Betancur-R. et al. 2019; Melo, Sidlauskas, et al. 2022), but also illuminating the effect of Gondwanan fragmentation on the distribution of characiforms in South America and Africa (Melo, Sidlauskas, et al. 2022). South American characiforms are paraphyletic relative to the clade containing the African Alestidae and Hepsetidae. The relaxed molecular clock age estimate for the divergence of African characiforms is consistent with the timing of the separation of South America and Africa (Melo, Sidlauskas, et al. 2022), validating Characiformes as an iconic example of continental-drift-driven vicariance in the diversification of freshwater lineages (Lundberg 1993; Ortí and Meyer 1997).

  • The earliest fossil Characiformes are from the Maastrichtian (72.2–66.0 Ma) in Bolivia and include intermediate teeth and skeletal fragments identified as species of Acestrorhynchidae, Characidae, and Serrasalmidae (Gayet et al. 2001, 2003). Isolated teeth from the Cenomanian (100.5–93.9 Ma) of Morocco are often cited as the earliest characiform fossils (Dutheil 1999; Malabarba and Malabarba 2010), but these teeth may be attributed to pan-lepisosteiforms (Cavin 2017:105). Bayesian relaxed molecular clock analyses of Characiformes result in an average posterior crown age estimate of 129.4 million years ago, with the credible interval ranging between 110.0 and 148.7 million years ago (Melo, Sidlauskas, et al. 2022).

  • img-z73-3_03.gif

    FIGURE 11.

    Phylogenetic relationships of the major living lineages and fossil taxa of Characiformes. Filled circles identify the common ancestor of clades, with formal names defined in the clade accounts.

    img-z71-1_03.jpg

    Euteleostei P. H. Greenwood, G. S. Myers,
    D. E. Rosen, and S. H. Weitzman 1967:227
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Lepidogalaxias salamandroides Mees 1961, Salmo salar Linnaeus 1758, and Perca fluviatilis Linnaeus 1758, but not Clupea harengus Linnaeus 1758. This is a minimum-crown-clade definition with an external specifier.

  • Etymology. From the ancient Greek εὖ (ˌiːj̍uː), meaning good or well; τέλειoς (t̍εlƗˌo͡Ʊz), meaning perfect or complete; and ὀστέoν (̍αːstIәn), meaning bone.

  • Registration number. 912.

  • Reference phylogeny. A phylogeny inferred from a phylogenomic dataset composed of DNA sequences from more than 1,100 exons (Hughes et al. 2018, fig. S2). Phylogenetic relationships among the major living and fossil lineages of Euteleostei are presented in Figure 7. The placement of the pan-argentiniform †Surlykus; the pan-salmoniforms †Barcarenichthys, †Kermichthys, †Pyrenichthys, and †Stompooria; the pan-stomiat †Nybelinoides; and the pan-osmeriform †Spaniodon are on the basis of inferences from morphology (Taverne 1982, 1992; Gayet and Lepicard 1985; Gayet 1988b; Anderson 1998; Fielitz 2002; Taverne and Filleul 2003; Guinot and Cavin 2018; Schrøder and Carnevale 2023).

  • Phylogenetics. Euteleostei is resolved as monophyletic in molecular phylogenetic studies that range from analysis of whole mtDNA genomes (J. Li, Xia, et al. 2010; Campbell, López, et al. 2013) to DNA sequences from multiple nuclear and mtDNA genes (Burridge et al. 2012; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; Davis et al. 2016), and phylogenomic datasets (Campbell, Alfaro, et al. 2017; Hughes et al. 2018; Straube et al. 2018; Rosas Puchuri 2021). A phylogenetic analysis of 42 morphological characters resolves the otocephalan lineage Alepocephaliformes nested within Euteleostei as the sister lineage of Argentiniformes, nests Stomiiformes in Neoteleostei, and places Esocidae (pikes and mudminnows) as the sister lineage of Neoteleostei (G. D. Johnson and Patterson 1996). A supertree analysis that utilized phylogenies resulting from morphological and molecular studies as input trees resolved Salmoniformes as the sister lineage of a clade named Zoroteleostei that includes all other euteleosts (M. V. H. Wilson and Williams 2010). The phylogenies of Euteleostei presented in G. D. Johnson and Patterson (1996) and Wilson and Williams (2010) are incongruent with trees inferred from molecular phylogenetic analyses (e.g., J. Li, Xia, et al. 2010; Near, Eytan, et al. 2012; Hughes et al. 2018).

  • One of the most remarkable results from molecular phylogenetic analyses of fishes is the resolution of the unique and enigmatic freshwater Lepidogalaxias salamandroides (Salamanderfish) as the sister lineage of all other Euteleostei (J. Li, Xia, et al. 2010; McDowall and Burridge 2011; Burridge et al. 2012; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; Campbell, López, et al. 2013; Davis et al. 2016; W. L. Smith et al. 2016; Campbell, Alfaro, et al. 2017; Hughes et al. 2018; Straube et al. 2018; Rosas Puchuri 2021; Mu et al. 2022). Within euteleosts, molecular studies consistently resolve three sets of sister lineages: Salmonidae (salmons and trouts) and Esocidae (includes Umbridae); Stomiiformes and Osmeriformes; and a lineage containing Galaxiidae (galaxiids) and Neoteleostei (Burridge et al. 2012; Near, Eytan, et al. 2012; Davis et al. 2016; Straube et al. 2018; Rosas Puchuri 2021). The phylogenetic relationships of Argentiniformes remain unresolved, with molecular studies resulting in four different hypotheses: as the sister lineage of the clade containing Salmonidae and Esocidae (C. H. Li et al. 2008; J. Li, Xia, et al. 2010; Near, Eytan, et al. 2012; Campbell, López, et al. 2013; Hughes et al. 2018; Straube et al. 2018; Rosas Puchuri 2021); the sister lineage of a clade containing Galaxiidae, Salmonidae, and Esocidae (Betancur-R, Broughton, et al. 2013); the sister lineage of a clade containing Stomiiformes, Osmeriformes, and Galaxiidae (Burridge et al. 2012); or as the sister lineage of a clade containing Stomiiformes, Osmeriformes, Galaxiidae, and Neoteleostei (Campbell, Alfaro, et al. 2017; Rosas Puchuri 2021).

  • Composition. Euteleostei currently consists of more than 21,405 species (Fricke et al. 2023) that include Lepidogalaxias salamandroides and species classified in Salmoniformes, Stomiatii, Argentiniformes, Galaxiidae, and Neoteleostei. Fossil taxa include the pan-argentiniform †Surlykus, the pan-stomiat †Nybelinoides (Taverne 1982), and the pan-salmoniforms †Kermichthys (Taverne 1992), †Barcarenichthys (Gayet 1988b, 1989), †Stompooria (Anderson 1998), and †Pyrenichthys (Gayet and Lepicard 1985). Details of the locations and ages of the fossil taxa are presented in Appendix 1. Over the past 10 years 1,789 new living species of Euteleostei have been described (Fricke et al. 2023), comprising 8.4% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Euteleostei include (1) presence of stegural, a membranous outgrowth of uroneural 1 (G. D. Johnson and Patterson 1996; Wiley and Johnson 2010), (2) caudal median cartilages present (G. D. Johnson and Patterson 1996; Wiley and Johnson 2010), and (3) unique supraneural shape (G. D. Johnson and Patterson 1996; Wiley and Johnson 2010). The first two of these proposed synapomorphies for Euteleostei are also present in Alepocephaliformes, which is nested in Otocephala and distantly related to Euteleostei (Figure 2).

  • Synonyms. Protacanthopterygii (Greenwood et al. 1966:366–387, 394–396; Wiley and Johnson 2010:141–143; Betancur-R et al. 2017:18), Zoroteleostei (M. V. H. Wilson and Williams 2010:404; J. S. Nelson et al. 2016:251), and Osmeromorpha (J. S. Nelson et al. 2016:252) are partial synonyms of Euteleostei. Euteleosteomorpha (Wiley and Johnson 2010:140; Betancur-R et al. 2017:18) is an ambiguous synonym of Euteleostei.

  • Comments. Along with Osteoglossomorpha, Elopomorpha, and Otocephala, Euteleostei is one of the four major clades of Teleostei (Dornburg and Near 2021). On its initial delimitation, Euteleostei included Ostariophysi (Greenwood et al. 1966, 1967), which was accepted in subsequent studies and classifications (Rosen 1973, 1974; Travers 1981; W. L. Fink and Weitzman 1982; Lauder and Liem 1983; W. L. Fink 1984a; J. S. Nelson 1984:117–119, 1994:124–125; Sanford 1990; Begle 1992). On the basis of the morphology of the teleost skull occipital region, Rosen (1985) suggested that ostariophysans, esocoids, and argentinoids are not euteleosts. Within Euteleostei, the presence of acellular bone was proposed as a synapomorphy for a clade containing Esocidae, Osmeriformes, and Neoteleostei (L. R. Parenti 1986). With the consistent resolution of Otocephala as a clade that includes Ostariophysi and Clupeiformes in molecular and morphological phylogenetic analyses (e.g., Lê et al. 1993; Lecointre and Nelson 1996; Arratia 1997; Near, Eytan, et al. 2012; Straube et al. 2018), classifications no longer include Ostariophysi in Euteleostei and thus closely match the composition of the clade to which we are applying that name (J. S. Nelson 2006:189; Wiley and Johnson 2010; J. S. Nelson et al. 2016:241; Betancur-R et al. 2017; Dornburg and Near 2021).

  • The earliest fossil Euteleostei is the pan-stomiat †Nybelinoides brevis from the Barremian and Aptian (126.5–113.2 Ma) of Belgium (Appendix 1; Taverne 1982; Guinot and Cavin 2018). Bayesian relaxed molecular clock analyses of Euteleostei result in an average posterior crown age estimate of 210.5 million years ago, with the credible interval ranging between 196.4 and 223.8 million years ago (Hughes et al. 2018).

  • img-z75-3_03.gif

    Argentiniformes G. D. Johnson and C. Patterson 1996:315
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Argentina sphyraena Linnaeus 1758 and Microstoma microstoma (Risso 1810). This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek ἀργύρεoς (̍αː͡ɹɡjjƱɹɹɪo͡Ʊz), meaning silvery. The suffix is from the Latin forma, meaning form, figure, or appearance.

  • Registration number. 913.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of 1,133 exons (Rosas Puchuri 2021, fig. 3.1). The phylogenetic relationships of the major lineages of Argentiniformes are presented in Figure 7.

  • Phylogenetics. Over the past century Argentiniformes was classified with combinations of Salmonidae (salmons and trouts), Alepocephaliformes, Galaxiidae (galaxiids), Osmeriformes, Stomiiformes, Esocidae (pikes and mudminnows), and Myctophiformes (Gosline 1960; Greenwood et al. 1966; G. J. Nelson 1970a). Greenwood and Rosen (1971) hypothesized that Argentiniformes and Alepocephaliformes are sister lineages as evidenced by the presence of a modified posterior pharyngobranchial structure they named the crumenal organ, which was the basis for the resolution of this clade in subsequent morphological studies (Begle 1992; G. D. Johnson and Patterson 1996). Molecular phylogenetic analyses consistently resolve Argentiniformes and Alepocephaliformes as distantly related: Alepocephaliformes is related to Clupeiformes and Ostariophysi in Otocephala and Argentiniformes is phylogenetically nested in Euteleostei (Figure 2; Ishiguro et al. 2003; Lavoué, Miya, Poulsen, et al. 2008; J. Li, Xia, et al. 2010; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; Davis et al. 2016; Campbell, Alfaro, et al. 2017; Hughes et al. 2018; Straube et al. 2018; Rosas Puchuri 2021).

  • Morphological and molecular phylogenetic analyses consistently support the monophyly of Argentiniformes (Begle 1992; Patterson and Johnson 1995; Ishiguro et al. 2003; J. Li, Xia, et al. 2010; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; Straube et al. 2018; Schrøder and Carnevale 2023). Phylogenetic analysis of morphological characters resolves Argentinidae (argentines) as the sister lineage of all other Argentiniformes, with Bathylagidae (deep-sea smelts) and Opisthoproctidae (barreleyes) as sister taxa (Rosen 1974) or Bathylagidae and Microstomatidae (pencilsmelts) as sister taxa (Patterson and Johnson 1995). Molecular phylogenetic analyses resolve the four major lineages of Argentiniformes into two sets of sister lineages: one clade containing Argentinidae and Opisthoproctidae and the other including Bathylagidae and Microstomatidae (J. Li, Xia, et al. 2010; Rosas Puchuri 2021).

  • Composition. There are currently 100 living species of Argentiniformes (Fricke et al. 2023) classified in Argentinidae, Bathylagidae, Microstomatidae, and Opisthoproctidae. Over the past 10 years there have been eight new living species of Argentiniformes described (Fricke et al. 2023), comprising 8.0% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Argentiniformes include (1) metapterygoid reduced in size (Begle 1992; G. D. Johnson and Patterson 1996; Wiley and Johnson 2010), (2) endopterygoid teeth absent (G. D. Johnson and Patterson 1996; Wiley and Johnson 2010), (3) parietal carrying commissural sensory canal (G. D. Johnson and Patterson 1996; Wiley and Johnson 2010), (4) premaxilla without teeth (G. D. Johnson and Patterson 1996; Wiley and Johnson 2010), (5) maxilla without teeth (G. D. Johnson and Patterson 1996; Wiley and Johnson 2010), (6) supramaxillae absent (G. D. Johnson and Patterson 1996; Wiley and Johnson 2010), (7) basibranchials 1-3 without teeth (G. D. Johnson and Patterson 1996; Wiley and Johnson 2010), (8) epibranchial 4 with distinct levator process (G. D. Johnson and Patterson 1996), (9) pharyngobranchial 2 without teeth (G. D. Johnson and Patterson 1996; Wiley and Johnson 2010), (10) pharyngobranchial 3 without teeth (G. D. Johnson and Patterson 1996; Wiley and Johnson 2010), and (11) supraneurals develop in “pattern 2” (G. D. Johnson and Patterson 1996).

  • Synonyms. Argentinoidei (Greenwood et al. 1966:394; Wiley and Johnson 2010:141) and Argentinoidea (Greenwood and Rosen 1971:39; J. S. Nelson 1984:160–162, 1994:179–181; Begle 1992:351; Johnson and Patterson 1996:309) are ambiguous synonyms of Argentiniformes.

  • Comments. Subsequent to the resolution of Alepocephaliformes within Otocephala (e.g., Ishiguro et al. 2003), classifications of Actinopterygii consistently use the group name Argentiniformes for the clade containing Argentinidae, Bathylagidae, Microstomatidae, and Opisthoproctidae (Davis et al. 2016; J. S. Nelson et al. 2016:252–254; Betancur-R et al. 2017; Dornburg and Near 2021).

  • The earliest fossils of Argentiniformes are otoliths from the Maastrichtian (72.2–66.0 Ma) of Maryland, USA, identified as Argentinidae and †Argentina voigti from Bavaria, Germany (Nolf and Stringer 1996; Schwarzhans 2010; Schwarzhans and Jagt 2021; Stringer and Schwarzhans 2021). The earliest skeletal argentiniform fossil is †Glossanodon musceli from the Rupelian (33.9–27.3 Ma) of the Czech Republic and Poland (Paucă 1929; Gregorová 2011; Přikryl et al. 2016). Relaxed molecular clock analyses estimate the crown age of Argentiniformes between 34.5 and 76.5 million years ago (Near, Eytan, et al. 2012).

  • img-z76-7_03.gif

    Salmoniformes P. H. Greenwood, D. E. Rosen,
    S. H. Weitzman, and G. S. Myers 1966:394

  • Definition. The least inclusive crown clade that contains Salmo salar Linnaeus 1758 and Esox lucius Linnaeus 1758. This is a minimum-crown-clade definition, but the clade is not defined using the PhyloCode.

  • Etymology. Salmo is Latin for Salmo trutta, dating to Pliny (N.H. 9.68) in the first century CE (Andrews 1955). The suffix is from the Latin forma, meaning form, figure, or appearance.

  • Reference phylogeny. A phylogeny inferred from a phylogenomic dataset consisting of DNA sequences from more than 1,100 exons (Hughes et al. 2018, fig. S2). Phylogenetic relationships of the major lineages of Salmoniformes are presented in Figure 7. The placements of the fossil taxa †Oldmanesox and †Estesesox in the phylogeny follow inferences from morphology (Brinkman et al. 2014).

  • Phylogenetics. Morphological studies result in a disparate set of phylogenetic relationships for Salmonidae (trouts and salmons) and Esocidae (pikes and mudminnows). Salmonidae are resolved as the sister lineage of Osmeriformes (Rosen 1974; G. D. Johnson and Patterson 1996); Galaxiidae (Rosen 1974); Neoteleostei (Lauder and Liem 1983; W. L. Fink 1984a); a clade containing Osmeriformes, Argentiniformes, and Alepocephaliformes (Sanford 1990); or unresolved among euteleosts (W. L. Fink and Weitzman 1982; Begle 1991, 1992). Morphological studies place Esocidae as the sister lineage of a clade containing Argentiniformes, Galaxiidae, Salmonidae, and Osmeriformes (Rosen 1974); a clade containing Salmonidae and Osmeriformes (Rosen 1974); the sister lineage of all other Euteleostei (W. L. Fink and Weitzman 1982; W. L. Fink 1984a; Sanford 1990; Begle 1991, 1992); or as the sister lineage of Neoteleostei (G. D. Johnson and Patterson 1996). One set of morphological studies resolves Salmonidae and Esocidae as sister lineages (R. R. G. Williams 1987; M. V. H. Wilson and Williams 2010), a result that is congruent with molecular phylogenetic analyses (Ishiguro et al. 2003; Lopez et al. 2004; Osinov and Lebedev 2004; C. H. Li et al. 2008; Davis 2010; J. Li, Xia, et al. 2010; Burridge et al. 2012; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; Campbell, López, et al. 2013; Faircloth et al. 2013; Davis et al. 2014, 2016; Campbell, Alfaro, et al. 2017; Hughes et al. 2018; Straube et al. 2018; Musilova et al. 2019; Harvey et al. 2021; Rosas Puchuri 2021; Mu et al. 2022).

  • Composition. Salmoniformes includes 275 species classified in Salmonidae and Esocidae (Fricke et al. 2023). Fossil taxa include the Cretaceous pan-esocids †Estesesox from the Campanian and Maastrichtian (83.2–66.0 Ma) of Montana, USA, and †Oldmanesox from the Campanian (83.2–72.2 Ma) of Alberta, Canada (M. V. H. Wilson et al. 1992). Details of the ages and locations of the fossil taxa are presented in Appendix 1. Over the past 10 years 30 new living species of Salmoniformes have been described, comprising 10.9% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Salmoniformes include (1) hyomandibular with unique process that extends towards the symplectic and metapterygoid (R. R. G. Williams 1987; M. V. H. Wilson and Williams 2010), (2) absence of distinct ligament connecting adductor mandibulae and maxilla-mandibular ligament (R. R. G. Williams 1987; M. V. H. Wilson and Williams 2010), and (3) absence of caudal scutes, median bony plates that form anterior to procurrent caudal fin rays [caudal scutes are also absent in Alepocephaliformes] (G. D. Johnson and Patterson 1996).

  • Synonyms. Protacanthopterygii (M. V. H. Wilson and Williams 2010:404; J. S. Nelson et al. 2016:243–251) is an ambiguous synonym of Salmoniformes.

  • Comments. The earliest fossil Salmoniformes are the western North American pan-esocids †Oldmanesox from the Campanian (83.6–72.1 Ma) and †Estesesox from the Campanian and Maastrichtian (72.1–66.0 Ma) (M. V. H. Wilson et al. 1992; Brinkman et al. 2014). Bayesian relaxed molecular clock analyses of Salmoniformes result in an average posterior crown age estimate of 82.8 million years ago, with the credible interval ranging between 76.8 and 88.3 million years ago (Hughes et al. 2018).

  • img-z77-7_03.gif

    Esocidae C. S. Rafinesque 1815:89

  • Definition. The least inclusive crown clade that contains Esox lucius Linnaeus 1758 and Umbra krameri Walbaum 1792. This is a minimum-crown-clade definition, but the clade is not defined using the PhyloCode.

  • Etymology. Isox is Latin, possibly Celtic or Basque in origin, which was the name for Salmo salar dating to Pliny (N.H. 9.44) in the first century CE (D. W. Thompson 1947:95; Andrews 1955).

  • Reference phylogeny. A phylogeny inferred from analysis of DNA sequences of 53 ultraconserved element (UCE) loci (Campbell, Alfaro, et al. 2017, fig. 1). Phylogenetic relationships of living and fossil lineages of Esocidae are presented in Figure 7. Placements of the fossil taxa †Boltyshia, †Palaeoesox, and †Proumbra in the phylogeny are on the basis of inferences from morphology (J. Gaudant 2012).

  • Phylogenetics. Relationships inferred from morphology place Esox as the sister lineage to a clade previously classified as Umbridae that contains Umbra, Dallia, and Novumbra (Cavender 1969; G. J. Nelson 1972; M. V. H. Wilson and Veilleux 1982); however, a study of meristic and morphometric traits noted the lack of morphological evidence for the monophyly of Umbridae (Reist 1987). To date, there is no phylogenetic investigation of Esocidae that employs explicit analysis of coded morphological character states. Molecular phylogenetic analyses consistently resolve Umbridae as paraphyletic, with Umbra placed as the sister lineage of all other Esocidae (Lopez et al. 2000, 2004; Burridge et al. 2012; Near, Eytan, et al. 2012; Campbell, López, et al. 2013; Campbell, Alfaro, et al. 2017; Marić et al. 2017; Pan et al. 2021). Several molecular phylogenetic studies are aimed at resolving relationships among species of Esox and providing a basis for species discovery and delimitation in the clade (T. Grande et al. 2004; Denys et al. 2014, 2018).

  • Composition. There are currently 13 living species of Esocidae (T. Grande et al. 2004; Lucentini et al. 2011; Denys et al. 2014; Kuehne and Olden 2014; Fricke et al. 2023). The species Dallia admirabilis Chereshnev and D. delicatissima are synonyms of Dallia pectoralis Bean (Campbell and Lopéz 2014; Dyldin et al. 2020). Fossil taxa of Esocidae include †Novumbra oregonensis from the Rupelian (33.90–27.82 Ma) in Oregon (Cavender 1969; Woodburne 2004), several species of Esox (M. V. H. Wilson 1980; L. Grande 1999), and the pan-umbrines †Boltyshia, †Palaeoesox, and †Proumbra (J. Gaudant 2012). Details of the ages and locations of the fossil taxa are given in Appendix 1. Over the past 10 years one new species of Esocidae has been described (Fricke et al. 2023), comprising 7.7% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Esocidae include (1) ethmoidal and antorbital canals present as pitlines (G. J. Nelson 1972; Rosen 1974), (2) presence of mandibulopreopercular, subnasal, and opercular pitlines (G. J. Nelson 1972; Rosen 1974), (3) presence of paired elongate proethmoids (Rosen 1974; G. D. Johnson and Patterson 1996; Wiley and Johnson 2010), (4) basibranchial tooth plate in two parts (G. D. Johnson and Patterson 1996; Wiley and Johnson 2010), (5) second pharyngobranchial conical in shape with tip enclosed in bone (G. D. Johnson and Patterson 1996; Wiley and Johnson 2010), (6) single upper pharyngeal tooth plate composed of upper fourth upper pharyngeal (G. D. Johnson and Patterson 1996; Wiley and Johnson 2010), and (7) presence of a single postcleithrum (G. D. Johnson and Patterson 1996; Wiley and Johnson 2010).

  • Synonyms. Esociformes (J. S. Nelson 1994:176–178, 2006:204–206; G. D. Johnson and Patterson 1996:316; López et al. 2004, fig. 2; J. S. Nelson et al. 2016:248–251; Betancur-R et al. 2017:18; Pan et al. 2021, fig. 1), Esocoidei (Berg 1940:429; Gosline 1960:358; Greenwood et al. 1966:394; G. J. Nelson 1972:32; J. S. Nelson 1984:157–159; Wiley and Johnson 2010:142), and Esocoidea (Rosen 1974:311) are ambiguous synonyms of Esocidae. Umbridae (Greenwood et al. 1966:394; G. J. Nelson 1972:32–33; Rosen 1974:311; J. S. Nelson 1984:158_159, 1994:177–178) and Esocinae (López et al. 2000:429) are partial synonyms of Esocidae.

  • Comments. As a consequence of molecular phylogenetic analyses (e.g., López et al. 2000, 2004; Campbell, Alfaro, et al. 2017), the classification of esociform fishes was modified by the inclusion of Dallia and Novumbra into Esocidae with Esox and limiting Umbridae to Umbra (J. S. Nelson 2006:205–206; J. S. Nelson et al. 2016:251). This change makes Umbra and Umbridae redundant group names. Historically, Esocidae and Umbridae were classified as Esocoidei (e.g., Wiley and Johnson 2010) or Esociformes (e.g., Betancur-R et al. 2017); however, these group names are redundant with Esocidae as delimited here. Esocidae is a valid family-group name under the International Code of Zoological Nomenclature (Van der Laan et al. 2014:64).

  • The earliest fossil Esocidae is †Esox tiemani from Tiffanian (60.2–56.8 Ma) North American Land Mammal Age dated rocks in Alberta, Canada (M. V. H. Wilson 1980; L. Grande 1999; Speijer et al. 2020, fig. 28.12) or †Boltyshia brevicauda from the Thanetian (59.2–56.0 Ma) in Ukraine (Cavagnetto and Gaudant 2000; J. Gaudant 2012). Bayesian relaxed molecular clock analyses of Esocidae result in an average posterior age estimate of 88.6 million years ago, with the credible interval ranging between 85.1 and 95.6 million years ago (Campbell, López, et al. 2013).

  • img-z79-2_03.gif

    Stomiatii R. Betancur-R, R. E. Broughton, E. O. Wiley, K. Carpenter, J. A. López, C. Li, N. I. Holcroft, D. Arcila, M. Sanciangco, J. C. Cureton II, F. Zhang, T. Buser, M. A. Campbell, J. A. Ballesteros, A. Roa-Varón, S. Willis, W. C. Borden, T. Rowley, P. C. Reneau, D. J. Hough, G. Lu, T. Grande, G. Arratia, and G. Ortí 2013: app. 2 [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Osmerus mordax (Mitchill 1814) and Stomias boa (Risso 1810). This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek στγµᾰ (st̍o͡Ʊmә), meaning mouth.

  • Registration number. 920.

  • Reference phylogeny. A phylogeny inferred from nine Sanger-sequenced nuclear genes (Near, Eytan, et al. 2012, fig. S1). Phylogenetic relationships of the living and fossil lineages of Stomiatii are presented in Figure 7. The placements of the pan-stomiiform †Paravinciguerria and the pan-osmeriform †Spaniodon are on the basis of inferences from morphology (Taverne and Filleul 2003; Carnevale and Rindone 2011).

  • Phylogenetics. A pre-phylogenetic morphological study proposed that Stomiiformes and Osmeridae exhibit a “relatively close relationship” (Weitzman 1967:523). Subsequent morphological studies resulted in varied and incongruent phylogenetic hypotheses among major lineages of Euteleostei and did not resolve Stomiatii as monophyletic (e.g., W. L. Fink 1984a; Rosen 1985; G. D. Johnson and Patterson 1996; Wilson and Williams 2010). Molecular phylogenetic analyses of Euteleostei consistently resolve Stomiatii as a monophyletic lineage that includes Osmeriformes and Stomiiformes (Davis 2010; J. Li, Xia, et al. 2010; Burridge et al. 2012; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; Campbell, López, et al. 2013; Davis et al. 2014, 2016; W. L. Smith et al. 2016; Campbell, Alfaro, et al. 2017; Malmstrøm et al. 2017; Hughes et al. 2018; Straube et al. 2018; Musilova et al. 2019; Rosas Puchuri 2021; Mu et al. 2022).

  • Composition. There are currently 500 living species of Stomiatii (Fricke et al. 2023) classified in Osmeriformes and Stomiiformes. Fossil lineages of Stomiatii include the pan-osmeriform †Spaniodon and the pan-stomiiform †Paravinciguerria (Appendix 1; Taverne and Filleul 2003; Carnevale and Rindone 2011). Over the past 10 years 31 new living species of Stomiatii have been described (Fricke et al. 2023), comprising 6.2% of the living species diversity in the clade.

  • Diagnostic apomorphies. There are no known morphological synapomorphies for Stomiatii (Betancur-R et al. 2017; Straube et al. 2018).

  • Synonyms. Stomiati (Betancur-R et al. 2017:18) is a variant spelling of Stomiatii.

  • Comments. Stomiatii is a group name applied to the clade containing Osmeriformes and Stomiiformes (Betancur-R, Broughton, et al. 2013).

  • The earliest fossil Stomiatii is the pan-stomiiform †Paravinciguerria praecursor from the Cenomanian (100.5–93.9 Ma) of Morocco and Sicily (Appendix 1; Khalloufi et al. 2010; Carnevale and Rindone 2011). Bayesian relaxed molecular clock analyses of Stomiatii result in an average posterior crown age estimate of 115.4 million years ago, with the credible interval ranging between 81.1 and 147.6 million years ago (Hughes et al. 2018).

  • img-z79-24_03.gif

    Stomiiformes W. L. Fink and S. H. Weitzman 1982:32
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Stomias boa (Risso 1810), Gonostoma denudatum Rafinesque 1810b, Sternoptyx diaphana Hermann 1781, and Vinciguerria nimbaria (Jordan and Williams in Jordan and Starks 1895). This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek στὀµᾰ (st̍o͡Ʊmә), meaning mouth. The suffix is from the Latin forma, meaning form, figure, or appearance.

  • Registration number. 922.

  • Reference phylogeny. A phylogeny of 99 species of Stomiiformes inferred from a supermatrix of 27 nuclear and mitochondrial genes (Rabosky et al. 2018; J. Chang et al. 2019). The phylogeny is available on the Dryad data repository (Rabosky et al. 2019). Phylogenetic relationships among the major lineages of Stomiiformes are presented in Figure 7.

  • Phylogenetics. Morphological phylogenetic studies consistently support the monophyly of Stomiiformes (Rosen 1973; Weitzman 1974; W. L. Fink and Weitzman 1982; W. L. Fink 1984b; Harold and Weitzman 1996; Harold 1998). Aside from phylogenies with limited taxon sampling (Harold and Weitzman 1996; Harold 1998), there is no morphological phylogenetic analysis of Stomiiformes that includes a comprehensive taxon sampling of the major lineages in the clade. Morphological phylogenetic analyses are aimed at stomiiform subclades: Sternoptychidae (marine hatchetfishes) (Harold 1993, 1994; Harold and Weitzman 1996), Gonostomatidae (bristlemouths) (Harold and Weitzman 1996; Harold 1998), and Stomiidae (barbeled dragonfishes) (W. L. Fink 1984b; W. L. Fink 1985). Weitzman (1974:338) introduced Phosichthyidae (lightfishes) to contain Pollichthys mauli (Stareye Lightfish), Phosichthys argenteus (Silver Lightfish), and Vinciguerria, Yarrella, Polymetme, Ichthyococcus, and Woodsia. There are no morphological apomorphies identified for Phosichthyidae and the group is resolved as paraphyletic in morphological studies (W. L. Fink 1984b; Harold and Weitzman 1996).

  • Molecular phylogenetic analyses resolve Stomiiformes as monophyletic (Miya et al. 2003; J. Li, Xia, et al. 2010; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; Davis et al. 2014, 2016; W. L. Smith et al. 2016; Rosas Puchuri 2021). A small number of molecular phylogenetic analyses include a sampling of the major lineages of Stomiiformes (Davis et al. 2014; Kenaley et al. 2014; Rabosky et al. 2018; Rosas Puchuri 2021). In analyses of DNA sequence data, the phosichthyid Vinciguerria is resolved as the sister lineage of all other Stomiiformes (Kenaley et al. 2014; Betancur-R et al. 2017; Rosas Puchuri 2021); however, analysis of translated amino acid sequences from more than 1,000 exons places Vinciguerria as nested well within Stomiiformes (Rosas Puchuri 2021). In molecular phylogenies, Stomiidae, Gonostomatidae, and Sternoptychidae are each resolved as monophyletic, but Phosichthyidae is deeply paraphyletic (Davis et al. 2014; Kenaley et al. 2014; Rabosky et al. 2018; Rosas Puchuri 2021). The former lineages of Phosichthyidae that include Pollichthys mauli, Polymetme, Yarrella, Vinciguerria, and Ichthyococcus do not resolve with other lineages that are delimited in named Linnaean taxonomic families (Figure 7; Rabosky et al. 2018; Rosas Puchuri 2021), and there are no available family-group names to accommodate any of these genera (Van der Laan et al. 2014). We delimit Phosichthyidae to include Phosichthys argenteus and species of Woodsia.

  • Composition. There are currently 458 living species of Stomiiformes (Fricke et al. 2023), including Pollichthys mauli and species classified in Ichthyococcus, Polymetme, Vinciguerria, Yarrella, Gonostomatidae, Phosichthyidae, Sternoptychidae, and Stomiidae. Over the past 10 years there have been 31 new living species of Stomiiformes described (Fricke et al. 2023), comprising 6.8% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Stomiiformes include (1) single broad termination of the second epibranchial that articulates with the second and third pharyngobranchials (Rosen 1973; W. L. Fink and Weitzman 1982; Wiley and Johnson 2010), (2) unique structure of the photophores (W. L. Fink and Weitzman 1982; Wiley and Johnson 2010), (3) type 3 tooth attachment (W. L. Fink and Weitzman 1982; Wiley and Johnson 2010), (4) medial section of adductor mandibulae divided into two sections, dorsal section inserting directly onto the maxilla and ventral portion inserting on primordial ligament (W. L. Fink and Weitzman 1982; Wiley and Johnson 2010), (5) unique crossing pattern of ethmoid-premaxillary ligament (W. L. Fink and Weitzman 1982; Wiley and Johnson 2010), (6) greatly enlarged posterior branchiostegal rays (W. L. Fink and Weitzman 1982; Wiley and Johnson 2010), (7) some branchiostegal rays articulating with ventral hypohyals (W. L. Fink and Weitzman 1982; Wiley and Johnson 2010), (8) rete mirabile located at posterior of swim bladder (W. L. Fink and Weitzman 1982; Wiley and Johnson 2010), (9) part of obliquus dorsalis 4 attached to fourth pharyngobranchial (Springer and Johnson 2004; Wiley and Johnson 2010), and (10) adductor 5 attaches to fourth epibranchial (Springer and Johnson 2004; Wiley and Johnson 2010).

  • Synonyms. Stomiatoidei (Jordan 1923:126–127; Gregory and Conrad 1936:25–27; Gosline 1960:358; Greenwood et al. 1966:372–373, 394; McAllister 1968:48–52; Weitzman 1974:338), Stomiatoidea (Beebe and Crane 1939:69), Stenopterygii (Rosen 1973:509), Stomiatiformes (Rosen 1973:509; Wiley and Johnson 2010:144; Betancur-R et al. 2017:144), and Stomiatia (Wiley and Johnson 2010:144) are ambiguous synonyms of Stomiiformes.

  • Comments. Prior to the development of phylogenetic systematics, lineages of Stomiiformes were consistently recognized as a natural group in taxonomic classifications (Regan 1923a; Gregory and Conrad 1936, fig. 3; Beebe and Crane 1939; Gosline 1960). The group name Stomiiformes has been applied to this clade since the early 1980s (W. L. Fink and Weitzman 1982; J. S. Nelson 1984:172–177, 1994:196–201, 2006:207–212; Near, Eytan, et al. 2012; Davis et al. 2016; J. S. Nelson et al. 2016:259–264; Dornburg and Near 2021), which is why it is selected as the clade name over its synonyms. While consistently resolved as monophyletic in phylogenetic analyses of Teleostei (e.g., Davis et al. 2014; Rabosky et al. 2018), relationships within Stomiiformes are not consistent among molecular analyses and there is no morphological phylogenetic study that includes a robust sampling of the major lineages in the clade. The lack of a robust understanding of the phylogenetic relationships within Stomiiformes is reflected by the deep paraphyly of Phosichthyidae, which prevents the establishment of a ranked Linnaean classification where the taxonomic families reflect monophyletic groups. The lineages not currently placed in Linnaean families are listed with generic names in the classification outlined in Appendix 2 and in the constituent lineages section below.

  • The earliest fossil Stomiiformes is †Eosternoptyx discoidalis, a species of Sternoptychidae from the Bartonian-aged (41.2–37.7 Ma) deposit in the Pabdeh Formation, Iran (Afsari et al. 2014). Relaxed molecular clock analyses estimate the crown age of Stomiiformes to be between 63 and 120 million years ago (Kenaley et al. 2014).

  • img-z81-6_03.gif

    Osmeriformes D. P. Begle 1991:46
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Osmerus eperlanus (Linnaeus 1758), Osmerus mordax (Mitchill 1814), and Retropinna semoni (Weber 1895). This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek σσµᾰ (h̍o͡Ʊsme͡I), meaning odor. The suffix is from the Latin forma, meaning form, figure, or appearance.

  • Registration number. 925.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of nine nuclear genes (Near, Eytan, et al. 2012, fig. S1). Although Osmerus eperlanus is not included in the reference phylogeny, it resolves in a clade with other species of Osmerus in a molecular phylogenetic analysis (Ilves and Taylor 2009, fig. 3). Phylogenetic relationships of living and fossil lineages of Osmeriformes are presented in Figure 7. Placement of the fossil taxon †Speirsaenigma in the phylogeny is on the basis of a phylogenetic analysis of morphological characters (M. V. H. Wilson and Williams 1991).

  • Phylogenetics. Among the multiple morphological studies of relationships among lineages of Euteleostei (McDowall 1969, 1984; G. J. Nelson 1970a; W. L. Fink and Weitzman 1982; W. L. Fink 1984a; Sanford 1990; Begle 1991; G. D. Johnson and Patterson 1996), only Rosen (1974:311) proposed a grouping of Osmeridae (smelts), Plecoglossus altivelis (Ayu), Salangidae (noodlefishes), and Retropinnidae (southern smelts) that is consistent with the current delimitation of Osmeriformes. Molecular phylogenetic analyses consistently resolve Osmeriformes as monophyletic (Waters et al. 2002; López et al. 2004; J. Li, Xia, et al. 2010; Near, Eytan, et al. 2012; Rabosky et al. 2018; Straube et al. 2018). Phylogenies inferred from morphology nest Plecoglossus and Salangidae within Osmeridae (Howes and Sanford 1987; G. D. Johnson and Patterson 1996); however, molecular studies resolve Osmeridae as monophyletic and the sister lineage of a clade containing Plecoglossus and Salangidae (Ilves and Taylor 2009; J. Li, Xia, et al. 2010; Burridge et al. 2012; Near, Eytan, et al. 2012; Rosas Puchuri 2021).

  • Composition. There are currently 42 living species of Osmeriformes (Fricke et al. 2023) that includes Plecoglossus altivelis and species classified in Osmeridae, Salangidae, and Retropinnidae. Fossil taxa of Osmeriformes include †Speirsaenigma lindoei from the Thanetian (59.2–56.0 Ma) in Alberta, Canada (Appendix 1; M. V. H. Wilson and Williams 1991; Lofgren et al. 2004). Over the past 10 years no new living species of Osmeriformes have been described.

  • Diagnostic apomorphies. In an effort to identify morphological apomorphies consistent with the monophyly of Osmeriformes, we used maximum parsimony as executed in Mesquite v. 3.70 (Maddison and Maddison 2021) to map 112 morphological character state changes reported in G. D. Johnson and Patterson (1996, app. 1) onto a phylogeny of Euteleostei that matches the tree in Figure 7. Relationships within Osmeridae and Retropinnidae matched those inferred in molecular phylogenetic analyses (Waters et al. 2002; Ilves and Taylor 2009). There is one character state change identified in the mapping exercise that appears as an unambiguous apomorphy; however, several other character state changes exhibit a pattern that is compelling for the hypothesis of osmeriform monophyly. The six characters include (1) pelvic girdle with ventral condyle (McDowall 1969, 1984; G. D. Johnson and Patterson 1996), (2) vomer without shaft [species of Salangidae have a vomer with a shaft and Plecoglossus lacks a vomer] (G. D. Johnson and Patterson 1996), (3) fifth epibranchial fused with fourth epibranchial at both ends [species of Plecoglossus, Prototroctes, and Stokellia have fifth epibranchial that is free or fused with fourth epibranchial only at its lower end] (G. D. Johnson and Patterson 1996), (4) epineural bones or ligaments originate on the centrum of several anterior vertebrate [the epineural bones or ligaments originate on the neural arch in species of Prototroctes and Retropinna] (G. D. Johnson and Patterson 1996), (5) cleithrum with narrow columnar process [cleithrum in species of Salangidae lacks a process] (McDowall 1969; G. D. Johnson and Patterson 1996), and (6) presence of an enlarged first pectoral radial that partially covers the scapula [the first pectoral radial is unmodified in species of Mallotus and Salangidae] (G. D. Johnson and Patterson 1996).

  • Synonyms. Osmeroidea (Rosen 1974:311) is an ambiguous synonym of Osmeriformes. Osmeroidei (G. D. Johnson and Patterson 1996:307; Wiley and Johnson 2010:142) is a partial synonym of Osmeriformes.

  • Comments. When first applied as a group name, Osmeriformes was delimited as a polyphyletic group that included Plecoglossus, Osmeridae, Salangidae, Retropinnidae, Argentiniformes, Alepocephaliformes, Lepidogalaxias, and Galaxiidae (Begle 1991; J. S. Nelson 1994:178–189); the paraphyletic group containing Plecoglossus, Osmeridae, Salangidae, Retropinnidae, Lepidogalaxias, and Galaxiidae (J. S. Nelson 2006:194–199); and the monophyletic group as delimited here (Davis et al. 2016; J. S. Nelson et al. 2016:256–259; Betancur-R et al. 2017; Rosas Puchuri 2021). The name Osmeriformes was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade.

  • The earliest fossil Osmeriformes is the pan-plecoglossid †Speirsaenigma lindoei from the Thanetian (59.2–56.0 Ma) in Alberta, Canada (M. V. H. Wilson and Williams 1991; Lofgren et al. 2004). Relaxed molecular clock analyses estimate the age of Osmeriformes to be between 80.0 and 125.7 million years ago (Near, Eytan, et al. 2012).

  • img-z83-3_03.gif

    Neoteleostei G. J. Nelson 1969a:534
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Ateleopus japonicus Bleeker 1853b (Ateleopodidae), Alepisaurus ferox Lowe 1833 (Aulopiformes), Scopelengys tristis Alcock 1890 (Myctophiformes), and Micropterus salmoides (Lacépède 1802) (Centrarchiformes), but not Osmerus mordax (Mitchill 1814) (Osmeriformes). This is a minimum-crown-clade definition with an external specifier.

  • Etymology. From the ancient Greek νέoϛ (n̍iːo͡Ʊz), meaning new; τέλειoς (t̍εlƗᵻo͡Ʊz), meaning perfect or complete; and ὀστέoν (̍αːstIәn), meaning bone.

  • Registration number. 926.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of nine concatenated Sanger-sequenced nuclear genes (Near, Eytan, et al. 2012, fig. S1). See Figures 2 and 12 for the phylogeny of lineages comprising Neoteleostei.

  • Phylogenetics. When initially delimited, Neoteleostei was represented in phylogenetic trees of the major lineages of vertebrates as a clade including Atherinoidei, Myctophiformes, Paracanthopterygii (sensu lato), and Acanthopterygii (G. J. Nelson 1969a). Neoteleostei was expanded to include Stomiiformes on the basis of three morphological synapomorphies (Rosen 1973); however, two of these traits were subsequently rejected on the basis of homology and phylogenetic incongruence (W. L. Fink and Weitzman 1982). The monophyly of a Neoteleostei that includes Stomiiformes was widely accepted in reviews of actinopterygian phylogeny and classification (Lauder and Liem 1983; Stiassny 1986; G. D. Johnson 1992; J. S. Nelson 1994, 2006; A. C. Gill and Mooi 2002; Stiassny et al. 2004; Wiley and Johnson 2010).

  • Molecular phylogenetic studies resolve Neoteleostei as a monophyletic group to the exclusion of Stomiiformes (Davis 2010; J. Li, Xia, et al. 2010; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; Davis et al. 2014, 2016; W. L. Smith et al. 2016; Malmstrøm et al. 2017; Hughes et al. 2018; Musilova et al. 2019; Mu et al. 2022). Within Neoteleostei molecular phylogenies resolve either Ateleopodidae (jellynose fishes) (e.g., Near, Eytan, et al. 2012), Aulopiformes (e.g., Hughes et al. 2018), or a clade containing Ateleopodidae and Aulopiformes (Mu et al. 2022) as the sister lineage of all other Neoteleostei. Morphology of the dorsal gill arch musculature suggests that Ateleopodidae forms a clade with Aulopiformes (Springer and Johnson 2004; Wiley and Johnson 2010). The uncertainty in the phylogenetic relationships of Ateleopodidae is a challenge to the delimitation of Eurypterygii, which is a hypothesized clade that includes Aulopiformes and Ctenosquamata (G. D. Johnson 1992). There is no morphological phylogenetic analysis of discretely coded morphological character state changes aimed at resolving relationships among the lineages of Neoteleostei.

  • Composition. Currently there are more than 20,460 living species of Neoteleostei (Fricke et al. 2023) classified in Ateleopodidae, Aulopiformes, and Ctenosquamata. Over the past 10 years there have been 1,707 new living species of Neoteleostei described (Fricke et al. 2023), comprising 8.3% of the living species diversity in the clade.

  • Diagnostic apomorphies. The morphological apomorphies proposed for Neoteleostei considered a delimitation of the clade that includes Stomiiformes. The apomorphies include (1) presence of retractor dorsalis (Rosen 1973; G. D. Johnson 1992; Olney et al. 1993; Wiley and Johnson 2010), (2) third internal levator inserts on fifth upper pharyngeal tooth plate (G. D. Johnson 1992; Olney et al. 1993; Wiley and Johnson 2010), (3) type 4 tooth attachment (G. D. Johnson 1992; Olney et al. 1993; Wiley and Johnson 2010), (4) transversus dorsalis attaches to second epibranchial (Springer and Johnson 2004; Wiley and Johnson 2010), and (5) presence of transversus epibranchialis 2 (Springer and Johnson 2004; Wiley and Johnson 2010).

  • Synonyms. There are no synonyms of Neoteleostei.

  • Comments. The monophyly of Neoteleostei is one of the key discoveries in the early efforts of applying phylogenetic systematics to the relationships of ray-finned fishes (G. J. Nelson 1969a; Rosen 1973). There have been slight modifications to the original delimitation of Neoteleostei, but the integrity of the clade remains largely intact (Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013). Neoteleostei is consistently applied as the group name for the clade as delimited here (Near, Eytan, et al. 2012; Davis et al. 2016; J. S. Nelson et al. 2016:264; Betancur-R et al. 2017; Hughes et al. 2018). Neoteleostei contains more than 58% of the living species diversity of ray-finned fishes and composes the dominant group of vertebrates occupying marine habitats.

  • The earliest fossil Neoteleostei is the aulopiform †Atolvorator longipectoralis from the Barremian (126.5–121.4 Ma) in the Cretaceous of Brazil (Gallo and Coelho 2008; Newbrey and Konishi 2015). Bayesian relaxed molecular clock analyses of Neoteleostei result in an average posterior crown age estimate of 161.0 million years ago, with the credible interval ranging between 152.2 and 172.0 million years ago (Hughes et al. 2018).

  • img-z85-7_03.gif

    FIGURE 12.

    Phylogenetic relationships of the major living lineages and fossil taxa of Neoteleostei, Aulopiformes, Ctenosquamata, Myctophiformes, Acanthomorpha, and Lampriformes. Filled circles identify the common ancestor of clades with formal names defined in the clade accounts. Open circles highlight clades with informal group names. Fossil lineages are indicated with a dagger (†). Details of the fossil taxa are presented in Appendix 1.

    img-z84-1_03.jpg

    Aulopiformes D. E. Rosen 1973:509
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Aulopus filamentosus (Bloch 1792a) and Alepisaurus ferox Lowe 1833. This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek αὐλωπίαϛ (ͻːl̍o͡Ʊpi͡әz) of unknown origin, a name applied to species of Scombridae by ancient Mediterranean authors (D. W. Thompson 1947:20–21). The suffix is from the Latin forma, meaning form, figure, or appearance.

  • Registration number. 928.

  • Reference phylogeny. A phylogeny inferred from a combined dataset of mitochondrial and nuclear gene DNA sequences and 138 morphological characters (Davis 2010, fig. 7). Phylogenetic relationships of living and fossil lineages of Aulopiformes are presented in Figure 12. The fossil taxa are placed in the phylogeny on the basis of analyses of morphological characters (Fielitz 2004; Davis and Fielitz 2010; Marramà and Carnevale 2017; Beckett, Giles, et al. 2018).

  • Phylogenetics. In pre-phylogenetic classifications, Aulopiformes and Myctophiformes were grouped together in Iniomi or a more inclusive Myctophiformes (e.g., Regan 1911a; Greenwood et al. 1966; Gosline 1971). Aulopiformes was first delimited as a monophyletic group in one of the earliest efforts to resolve the phylogenetic relationships of Euteleostei (Rosen 1973). Several phylogenetic analyses using morphological characters inferred paraphyly of Aulopiformes (R. K. Johnson 1982; Rosen 1985; Hartel and Stiassny 1986); however, subsequent morphological and molecular studies resolved the lineage as monophyletic (G. D. Johnson 1992; Baldwin and Johnson 1996; Sato and Nakabo 2002; Fielitz 2004; Davis 2010; Fielitz and González-Rodríguez 2010). The most comprehensive phylogeny of Aulopiformes is one resulting from analysis of combined morphological and molecular characters (Davis 2010). Incongruence in the phylogenies inferred from the combined morphological and molecular dataset and those based solely on morphological characters involve the relationships of Alepisaurus (lancetfishes and daggertooths), Bathysauropsis (black lizardfishes), Chlorophthalmidae (greeneyes), Evermannellidae (sabertooth fishes), Ipnopidae (deep-sea tripod fishes), Notosudidae (waryfishes), Paralepididae (barracudinas), and Sudis (Baldwin and Johnson 1996; Sato and Nakabo 2002; Davis 2010). Analysis of morphological characters resolves the phylogenetic relationships of fossil lineages of Aulopiformes that include †Argillichthys, †Apateodus, †Cimolichthys, †Enchodontoidei, †Holosteus, †Labrophagus, and †Pavlovichthys (Fielitz 2004; Davis and Fielitz 2010; Fielitz and González-Rodríguez 2010; H. M. A. Silva and Gallo 2011; Cavin et al. 2012; Marramà and Carnevale 2017; Beckett, Giles, et al. 2018; Díaz-Cruz et al. 2020, 2021).

  • Composition. There are 298 living species of Aulopiformes (Fricke et al. 2023), including Alepisaurus, Bathysauroides gigas (Pale Deepsea Lizardfish) and species classified in Bathysaurus, Bathysauropsis, Gigantura (telescopefishes), Paraulopus (cucumberfishes), Pseudotrichonotus (sand-diving lizardfishes), Sudis, Aulopidae (flagfins), Chlorophthalmidae, Evermannellidae, Ipnopidae, Notosudidae, Paralepididae, Scopelarchidae (pearleyes), and Synodontidae (lizardfishes). Fossil taxa of Aulopiformes include †Apateodus, †Cimolichthys, †Argillichthys, †Labrophagus, †Enchodontoidei, †Holosteus, and †Pavlovichthys (Fielitz and González-Rodríguez 2010; Marramà and Carnevale 2017; Beckett, Giles, et al. 2018; Díaz-Cruz et al. 2020, 2021). Details of the ages and locations of the fossil taxa are given in Appendix 1. Over the past 10 years 25 new species of Aulopiformes have been described (Fricke et al. 2023), comprising 8.4% of the species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies of Aulopiformes include (1) presence of elongate uncinate process on second epibranchial (Rosen 1973; Sato and Nakabo 2002; Davis 2010; Beckett, Giles, et al. 2018), (2) cartilaginous condyle on dorsal surface of third pharyngobranchial does not articulate with second epibranchial (G. D. Johnson 1992; Baldwin and Johnson 1996; Sato and Nakabo 2002; Davis 2010; Wiley and Johnson 2010), (3) fourth epibranchial with enlarged proximal end capped with a large band of cartilage and uncinate process at middle portion (Sato and Nakabo 2002; Davis 2010; Beckett, Giles, et al. 2018), (4) presence of fifth epibranchial (Baldwin and Johnson 1996; Sato and Nakabo 2002; Davis 2010; Beckett, Giles, et al. 2018), (5) ventral portion of palatine not expanded laterally (Sato and Nakabo 2002; Davis 2010), (6) posterior placement of the palatine cartilaginous facet for articulation with lateral ethmoid (Sato and Nakabo 2002; Davis 2010), (7) epipleurals extend anteriorly to at least second vertebrae (Patterson and Johnson 1995; Baldwin and Johnson 1996; Sato and Nakabo 2002; Davis 2010; Wiley and Johnson 2010), (8) one or more epipleurals displaced dorsally into horizontal septum (Patterson and Johnson 1995; Baldwin and Johnson 1996; Davis 2010; Wiley and Johnson 2010), (9) some ribs ossify in membrane bone (Baldwin and Johnson 1996; Davis 2010), (10) proximal portion of principal caudal-fin rays with modified segment (Baldwin and Johnson 1996; Sato and Nakabo 2002; Davis 2010), (11) medial process of pelvic girdle joined with cartilage (Baldwin and Johnson 1996; Sato and Nakabo 2002; Davis 2010; Wiley and Johnson 2010), (12) presence of two adductor profundus elements, (13) absence of swim bladder (R. K. Johnson 1982; Baldwin and Johnson 1996; Sato and Nakabo 2002; Davis 2010; Wiley and Johnson 2010), and (14) presence of head spines on larvae (Baldwin and Johnson 1996; Sato and Nakabo 2002; Davis 2010).

  • Synonyms. Scopeliformes (Gosline 1961:10–11), Cyclosquamata (Rosen 1973:509; Betancur-R et al. 2017:19), and Aulopa (Wiley and Johnson 2010:144) are ambiguous synonyms of Aulopiformes. Iniomi is a partial synonym of Aulopiformes (Gosline et al. 1966:1-2).

  • Comments. Aulopiformes has been consistently used as the group name for the clade outlined in the definition (Rosen 1973; W. L. Fink 1984a; Davis 2010; Wiley and Johnson 2010; Davis et al. 2016; J. S. Nelson et al. 2016:266–276) and is chosen as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade.

  • Eight of the 15 taxonomic families of Aulopiformes contain either a single species or a single genus (Davis 2010). Future efforts aimed at reducing group names in the phylogenetic-based classification of Aulopiformes could place Harpadon, Pseudotrichonotus, Saurida, Synodus, and Trachinocephalus into Aulopidae; Bathysaurus and Bathysauroides gigas into Giganturidae; and Bathysauropsis into Ipnopoidae.

  • The earliest fossil Aulopiformes is †Atolvorator longipectoralis from the Barremian (129.4–121.4 Ma) in Brazil (Gallo and Coelho 2008; Newbrey and Konishi 2015). The phylogenetic affinities of †Atolvorator within Aulopiformes are unresolved (Gallo and Coelho 2008). Bayesian relaxed molecular clock analyses of Aulopiformes result in an average posterior crown age estimate of 140 million years ago, with the credible interval ranging between 127 and 156 million years ago (Davis and Fielitz 2010).

  • img-z87-4_03.gif

    Ctenosquamata D. E. Rosen 1973
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Scopelengys tristis Alcock 1890 and Micropterus salmoides (Lacépède 1802). This is a minimum-crown-clade definition.

  • Etymology. Derived from the ancient Greek κτείς (t̍iːnIs), meaning comb, and the Latin squama, meaning scale.

  • Registration number. 929.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of nine concatenated Sanger-sequenced nuclear genes (Near, Eytan, et al. 2012, figs. 1, S1). Phylogenetic relationships of the major lineages of Ctenosquamata are presented in Figures 2 and 12. The placement of the fossil taxa †Ctenothrissiformes, †Sardinoides, and †Neocassandra are on the basis of analysis and inferences from morphological characters (M. Gaudant 1978b, 1979; Prokofiev 2006a; Dietze 2009; Davesne et al. 2016).

  • Phylogenetics. In a groundbreaking study of euteleost phylogeny on the basis of osteology and musculature of the jaws, pharyngobranchials, and caudal skeleton, Rosen (1973) introduced the group name Ctenosquamata for the clade containing Myctophiformes and Acanthomorpha. Rosen (1973) argued that Myctophiformes, comprising Myctophidae and Neoscopelidae, was more closely related to Acanthomorpha, in contrast to traditional classifications that grouped Aulopiformes with Myctophiformes (e.g., Regan 1911a; Jordan 1923:153–156; Berg 1940:437–438; Gosline et al. 1966; R. K. Johnson 1982). In a study of occipital anatomy, Rosen (1985) later rejected the monophyly of Ctenosquamata, proposing a phylogenyinwhichMyctophidae(lanternfishes) and Acanthomorpha share a common ancestry to the exclusion of Neoscopelidae (blackchins). Johnson (1992) convincingly pointed out problems in the interpretation of character variation in Rosen (1985) and reviewed evidence for the monophyly of Ctenosquamata.

  • The monophyly of Ctenosquamata is supported in phylogenetic analyses of discretely coded morphological characters (Stiassny 1996; Wiley et al. 1998; Dietze 2009). Manual cladistic solutions representing ctenosquamate monophyly (Lauder and Liem 1983; Stiassny 1986) and other summary phylogenies of ray-finned fishes and teleosts depict monophyly of Ctenosquamata (W. L. Fink and Weitzman 1982; Rosen 1982; W. L. Fink 1984a; G. J. Nelson 1989; G. D. Johnson 1992; C. D. Roberts 1993; Yamaguchi 2000; A. C. Gill and Mooi 2002; Springer and Johnson 2004). Phylogenetic analysis of morphological characters resolves the Late Cretaceous †Ctenothrissiformes and Acanthomorpha as sister lineages (Davesne et al. 2016; Cantalice et al. 2021), a result consistent with a pre-cladistic study (Patterson 1964). Studies by M. Gaudant (1978b, 1979) hypothesized that †Ctenothrissiformes are stem lineage ctenosquamates.

  • Molecular phylogenetic analyses consistently resolve Ctenosquamata as monophyletic (Wiley et al. 1998; Alfaro, Santini, et al. 2009; Davis 2010; Betancur-R, Broughton, et al. 2013; T. Grande et al. 2013; Poulsen et al. 2013; W.-J. Chen, Santini, et al. 2014; Davis et al. 2014, 2016; Denton 2014; Malmstrøm et al. 2016; W. L. Smith et al. 2016; Mirande 2017; Hughes et al. 2018; Martin et al. 2018; Mu et al. 2022; J.-F. Wang et al. 2023). In a maximum parsimony analysis of complete mtDNA genomic sequences, the ateleopid lineages Ateleopus and Ijimaia are nested in Ctenosquamata (Miya et al. 2001, 2003), but subsequent analyses using model based phylogenetic analysis of complete mtDNA genomic sequences result in ctenosquamate monophyly (Poulsen et al. 2013; J.-F. Wang et al. 2023).

  • Composition. Ctenosquamata includes more than 21,150 living species (Fricke et al. 2023) classified in Acanthomorpha and Myctophiformes. Fossil taxa of Ctenosquamata include the pan-acanthomorph †Ctenothrissiformes (Patterson 1964; M. Gaudant 1978b; Davesne et al. 2016) and the pan-myctophiforms †Sardinoides monasteri and †Neocassandra mica (Prokofiev 2006a; Dietze 2009). Details on the ages and locations of the fossil taxa are given in Appendix 1. Over the past 10 years there have been 1,681 new living species of Ctenosquamata described (Fricke et al. 2023), comprising 8.3% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Ctenosquamata include (1) absences of fifth upper pharyngeal tooth plates and associated third levatores interni (G. D. Johnson 1992; Olney et al. 1993; Stiassny 1996; Wiley and Johnson 2010), (2) two or fewer branchiostegal rays on posterior ceratohyal (McAllister 1968; Stiassny 1996; Wiley and Johnson 2010), (3) loss of craniotemporalis musculature (Stiassny 1986, 1996; Wiley and Johnson 2010), (4) absence of supraorbital bones (Stiassny 1996; Wiley and Johnson 2010), and (5) presence of single and medially fused neural arch on first vertebral centrum (Stiassny 1996; Wiley and Johnson 2010).

  • Synonyms. There are no synonyms of Ctenosquamata.

  • Comments. The earliest fossil Ctenosquamata includes several pan-lampriforms, pan-acanthopterygians, pan-holocentrids, pan-trachichthyiforms, pan-percomorphs, and †Ctenothrissa signifer from the Cenomanian (100.5–93.2 Ma) in the Cretaceous of Lebanon (Bannikov and Bacchia 2005; Davesne et al. 2016). Bayesian relaxed molecular clock analyses of Ctenosquamata result in an average posterior crown age estimate of 149.7 million years ago, with the credible interval ranging between 141.8 and 159.1 million years ago (Hughes et al. 2018).

  • img-z88-8_03.gif

    Myctophiformes C. T. Regan 1911a:121
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Neoscopelus macrolepidotus J. Y. Johnson 1863 and Myctophum punctatum Rafinesque 1810b. This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek µυκτήρ (mˈuːktɚ), meaning nose, and όφίς (ˈo͡Ʊfiz), meaning snake. The suffix is from the Latin forma, meaning form, figure, or appearance.

  • Registration number. 930.

  • Reference phylogeny. A phylogeny inferred from a combined analysis of phylogenomic data (UCEs), Sanger-sequenced mtDNA and nuclear genes, and morphology (Martin et al. 2018, fig. 4). Phylogenetic relationships of living and fossil lineages of Myctophiformes are presented in Figure 12. The placements of fossil taxa in the phylogeny are on the basis of inferences from morphology (Prokofiev 2006a; Dietze 2009).

  • Phylogenetics. The first phylogenies of Myctophiformes inferred from morphological characters included nearly every genus (Paxton et al. 1984; Stiassny 1996), but did not include outgroups to test monophyly of the taxon. A phylogenetic analysis that sampled 60 morphological characters from taxa representing Acanthomorpha, Aulopiformes, Myctophidae (lanternfishes), Neoscopelidae (blackchins), and Stomiiformes resolves Myctophiformes as monophyletic (Dietze 2009). The monophyly of Myctophiformes is supported in morphological analyses (Stiassny 1986, 1996; Yamaguchi 2000). A combined analysis of morphology, mtDNA, Sanger-sequenced nuclear genes, and next-generation sequenced UCE loci strongly supports the monophyly of Myctophiformes (Martin et al. 2018). One analysis of partial mtDNA rRNA genes resolves Myctophiformes as paraphyletic (Colgan et al. 2000); however, all other phylogenetic analyses of molecular data result in myctophiform monophyly (e.g., Miya et al. 2001, 2003; Davis 2010; Near, Eytan, et al. 2012, 2013; Poulsen et al. 2013; W.-J. Chen, Santini, et al. 2014; Davis et al. 2014, 2016; Denton 2014; W. L. Smith et al. 2016; Martin et al. 2018).

  • Composition. Myctophiformes currently contains 258 living species (Paxton and Hulley 1999a, 1999b; Fricke et al. 2023), classified in Myctophidae and Neoscopelidae. Fossil lineages of Myctophiformes include the pan-neoscopelid †Beckerophotus and the pan-myctophid †Eomyctophum. Details of the ages and locations of the fossil taxa are given in Appendix 1. Over the past 10 years there was one new species of Myctophiformes described (Fricke et al. 2023), comprising 0.4% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Myctophiformes include (1) median dorsal keel present on mesethmoid (Stiassny 1986, 1996; Wiley and Johnson 2010), (2) median maxilla-premaxillary ligaments (VIII) insert on the contralateral buccal elements (Stiassny 1986, 1996; Wiley and Johnson 2010), (3) large tooth plate fused to proximal end of fourth ceratobranchial (Stiassny 1996; Wiley and Johnson 2010), (4) absence or reduction of first levator externus (Stiassny 1996; Wiley and Johnson 2010), (5) parapophyses on first vertebral centrum are cone-like and enlarged and meet at ventral midline (Stiassny 1986, 1996; Wiley and Johnson 2010), (6) adipose fin support inserted ventrally into supracarinalis posterior muscle mass (Stiassny 1996; Wiley and Johnson 2010), (7) presence of tranversus paryngobranchiales 2a and 2b (Springer and Johnson 2004; Wiley and Johnson 2010), (8) single fused extrascapular (Martin et al. 2018), and (9) narrow pubic plate (Martin et al. 2018).

  • Synonyms. Myctophata (Wiley and Johnson 2010:146; Betancur-R et al. 2017:19) and Scopelomorpha (Rosen and Patterson 1969:460; Rosen 1973:509; J. S. Nelson et al. 2016:276) are ambiguous synonyms of Myctophiformes. Myctophoidei (Greenwood et al. 1966:395) is a partial synonym of Myctophiformes.

  • Comments. Prior to Rosen's (1973) proposal limiting Myctophiformes to Myctophidae and Neoscopelidae, earlier classifications considered Myctophiformes or Iniomi to include Aulopiformes, Myctophidae, and Neoscopelidae (e.g., Regan 1911a; Greenwood et al. 1966; Gosline 1971). Scientists questioned the reality of Iniomi as early as the late 19th century (e.g., T. N. Gill 1893). In the first 10 years after Rosen (1973) some authors continued to recognize this heterogeneous concept of Myctophiformes (R. K. Johnson 1982; Okiyama 1984). Convincing evidence for the delimitation of Myctophiformes followed here came from detailed and thorough morphological analyses (Stiassny 1986, 1996). Essentially all molecular analyses have supported the monophyly of Myctophiformes (e.g., Near, Eytan, et al. 2012; Poulsen et al. 2013; Davis et al. 2014), demonstrating that as much as molecular phylogenies dramatically affect teleost classifications, they are also corroborative for well-supported but contentious hypotheses proposed as a result of analysis of morphological data. The name Myctophiformes was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade.

  • The earliest fossil Myctophiformes are two pan-myctophids: the otolith taxon †Eokrefftia prediaphus from the Thanetian (59.2–56.0 Ma) of South Australia and the skeletal taxon †Eomyctophum broncus from the Ypresian (56.0–48.1 Ma) of New Zealand (Schwarzhans 2019; Schwarzhans and Carnevale 2021). Bayesian relaxed molecular clock analyses of Myctophiformes result in an average posterior crown age estimate of 69.0 million years ago, with the credible interval ranging between 60.1 and 78.7 million years ago (Near et al. 2013).

  • img-z90-3_03.gif

    Acanthomorpha D. E. Rosen 1973:510
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Lampris guttatus (Brünnich 1788), Polymixia lowei Günther 1859, Percopsis omiscomaycus (Walbaum 1792), Zeus faber Linnaeus 1758, Stylephorus chordatus Shaw 1791, Gadus morhua Linnaeus 1758, Diretmus argenteus Johnson 1864, Beryx decadactylus Cuvier 1829 in Cuvier and Valenciennes (1829a), Carapus bermudensis (Jones 1874), and Micropterus salmoides (Lacépède 1802). This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek μκανθα (æk̍ænθә), meaning thorn or spine, and µoρϕή (m̍ͻ͡ʊfiz), meaning form or shape.

  • Registration number. 931.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of 989 ultraconserved element (UCE) loci (Ghezelayagh et al. 2022, figs. S1–S25). Phylogenetic relationships among the major living and fossil lineages of Acanthomorpha are presented in Figures 2 and 12. Phylogenetic placements of fossil taxa are on the basis of inferences from morphological analyses (Davesne et al. 2014, 2016; Delbarre et al. 2016; Cantalice et al. 2021).

  • Phylogenetics. Phylogenetic analyses of discretely coded morphological character state changes resolve Acanthomorpha as monophyletic (Stiassny 1986; Stiassny and Moore 1992; G. D. Johnson and Patterson 1993; Davesne et al. 2016; Cantalice et al. 2021). Relationships within acanthomorphs differ among morphological analyses, but several studies resolve Lampriformes as the sister lineage to all other acanthomorphs and Holocentridae as the sister lineage of Percomorpha (Stiassny and Moore 1992; Olney et al. 1993; Davesne et al. 2016; Cantalice et al. 2021).

  • Molecular phylogenetic analyses using mtDNA, nuclear genes, or combinations of the two and phylogenomic analyses consistently resolve Acanthomorpha as monophyletic (W.-J. Chen et al. 2003; Miya et al. 2003, 2005; W. L. Smith and Wheeler 2006; Alfaro, Santini, et al. 2009; Santini et al. 2009; Davis 2010; Near, Eytan, et al. 2012, 2013; Betancur-R, Broughton, et al. 2013; T. Grande et al. 2013; W.-J. Chen, Santini, et al. 2014; Davis et al. 2016; Malmstrøm et al. 2016; W. L. Smith et al. 2016; Betancur-R et al. 2017; Hughes et al. 2018; Musilova et al. 2019; Roth et al. 2020; Ghezelayagh et al. 2022; Mu et al. 2022). However, relationships among the major lineages of Acanthomorpha vary across studies. Phylogenomic analyses consistently resolve three major clades: Lampriformes, Paracanthopterygii, and Acanthopterygii (Alfaro et al. 2018; Hughes et al. 2018; Musilova et al. 2019; Ghezelayagh et al. 2022). Trees inferred from phylogenomic analyses of exons resolve Lampriformes as the sister lineage of Acanthopterygii (Hughes et al. 2018; Musilova et al. 2019; Roth et al. 2020), while phylogenomic analyses of UCE loci and a set of 82 exons place Lampriformes as the sister lineage of Paracanthopterygii (Alfaro et al. 2018; Ghezelayagh et al. 2022; Mu et al. 2022). Bayesian concordance factors estimated using UCE data find that resolution of Lampriformes as sister of Paracanthopterygii is supported by the greatest proportion of sampled loci; however, the 95% highest posterior density of the concordance factors overlaps with that of the phylogeny that resolves Lampriformes and Acanthopterygii as sister lineages (Ghezelayagh et al. 2022), suggesting relationships among lineages of Acanthomorpha are not confidently resolved.

  • Composition. Acanthomorpha currently includes more than 19,895 living species (Fricke et al. 2023), classified in the subclades Lampriformes, Paracanthopterygii, and Acanthopterygii. Fossil lineages include the pan-lampriforms †Aipichthys, †Aipichthyoides, †Nardovelifer, and †Zoqueichthys (Patterson 1964; Alvarado-Ortega and Than-Marchese 2012; Murray and Wilson 2014; Davesne et al. 2016; Delbarre et al. 2016; Cantalice et al. 2021); the pan-paracanthopterygian †Pycnosteroides (Patterson 1964, 1993; Davesne et al. 2016; Cantalice et al. 2021); and the pan-acanthopterygian †Choichix (Cantalice et al. 2021). Details of the ages and locations of the fossil taxa are given in Appendix 1. Over the past 10 years 1,680 new species of Acanthomorpha have been described (Fricke et al. 2023), comprising 8.4% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Acanthomorpha include (1) anterior facets on the first vertebral centrum that articulate with the exoccipital condyles (Rosen 1985; G. D. Johnson and Patterson 1993; Wiley and Johnson 2010), (2) maxillo-rostroid ligament originates from inner portion of maxillary median process and inserts onto rostral cartilage (Stiassny 1986; Olney et al. 1993; Wiley and Johnson 2010), (3) spina occipitalis extends ventrally, forming dorsal margin of the foramen magnum (Stiassny 1986; Olney et al. 1993), (4) anterior extension of lateral ethmoid located close to, or sutured with, lateral process projecting from ventral stalk of vomer (Stiassny 1986; Olney et al. 1993; Davesne et al. 2016; Cantalice et al. 2021), (5) upper limb of posttemporal bound to epioccipital with a reduced posttemporal-epioccipital ligament (Stiassny 1986; Olney et al. 1993), (6) distal ossification of medial pelvic process (G. D. Johnson and Patterson 1993; Wiley and Johnson 2010), (7) separated medial and anterior infracarinales muscles (G. D. Johnson and Patterson 1993; Stiassny 1993; Wiley and Johnson 2010), (8) presence of unsegmented, bilaterally fused dorsal and anal fin spines (G. D. Johnson and Patterson 1993; Wiley and Johnson 2010; Davesne et al. 2016; Cantalice et al. 2021), (9) absence of median caudal cartilages (G. D. Johnson and Patterson 1993; Wiley and Johnson 2010), and (10) antorbital bone absent (Cantalice et al. 2021).

  • Synonyms. Acanthomorphata (Wiley and Johnson 2010:127, 146–147; Betancur-R et al. 2017:20) is an ambiguous synonym of Acanthomorpha.

  • Comments. Acanthomorpha, or spiny-rayed fishes, comprise one of the major inclusive lineages of teleost fishes and the name Acanthomorpha is here defined as applying to the clade originating in their most recent common ancestor. Since the recognition and delimitation of Acanthomorpha by Rosen (1973), the major living lineages that comprise this taxon have not changed. The discovery of support for acanthomorph monophyly and the phylogenetic relationships of its constituent lineages (Stiassny 1986; G. D. Johnson and Patterson 1993; Near, Eytan, et al. 2012) remains an active area of research. Recent Sanger sequencing and phylogenomic studies provide unprecedented taxon sampling and resolution for acanthomorph phylogenetic relationships (Betancur-R, Broughton, et al. 2013; Near et al. 2013; Alfaro et al. 2018; Ghezelayagh et al. 2022).

  • The earliest fossils of Acanthomorpha date to the Cenomanian (100.5–93.9 Ma) (Patterson 1993; Friedman 2010; Murray 2016). Bayesian relaxed molecular clock analyses of Acanthomorpha result in an average posterior crown age estimate of 144.8 million years ago, with the credible interval ranging between 136.9 and 152.3 million years ago (Ghezelayagh et al. 2022).

  • img-z91-8_03.gif

    Lampriformes G. C. Steyskal 1980:171
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Lampris guttatus (Brünnich 1788), Metavelifer multiradiatus (Regan 1907a), and Regalecus russelii (Cuvier 1816), but not Stylephorus chordatus Shaw 1791. This is a minimum-crown-clade definition with an external specifier.

  • Etymology. From the ancient Greek λαµπῥoς (l̍æmpɹo͡Ʊz) meaning bright, brilliant, or radiant. The suffix is from the Latin forma meaning form, figure, or appearance.

  • Registration number. 932.

  • Reference phylogeny. A phylogeny of Lampriformes inferred from analysis of seven Sanger-sequenced nuclear genes (Brownstein and Near 2023, fig. 4). Phylogenetic relationships of the living and fossil lineages of Lampriformes are presented in Figure 12. The placements of the fossil lampriform taxa in the phylogeny are on the basis of inferences from morphology (Bannikov 1999; Gottfried et al. 2006; Brownstein and Near 2023).

  • Phylogenetics. The phylogenetic relationships within Lampriformes have been investigated with analyses of morphological and molecular datasets (Oelschläger 1983; Olney et al. 1993; Wiley et al. 1998; T. R. Roberts 2012; Martin 2015). The morphological phylogenies presented in Olney et al. (1993) and Martin (2015), and the molecular phylogeny in Wiley et al. (1998) are congruent in the resolution of Veliferidae (velifers) as the sister lineage of all other Lampriformes and Lampris (opahs) as the sister lineage of a clade containing Lophotidae (crest-fishes), Radiicephalus (tapertails), Regalecidae (oarfishes), and Trachipteridae (ribbonfishes). A molecular phylogeny inferred from mtDNA and nuclear genes resolves a clade containing Lampris and Veliferidae that is the sister lineage of all other Lampriformes (Rabosky et al. 2018; J. Chang et al. 2019), which is consistent with the classification that grouped Lampris and Veliferidae in Bathysomi and all other lineages of lampriforms in Taeniosomi (Regan 1907b). A series of morphological phylogenetic analyses that included multiple species of Lampriformes were aimed at investigating the relationships of several pan-lampriform fossil taxa (Davesne et al. 2014, 2016; Delbarre et al. 2016; Cantalice et al. 2021).

  • The two earliest morphological phylogenetic analyses of Oelschläger (1983) and Olney et al. (1993) include Stylephorus chordatus as this species was long classified with lineages of Lampriformes (Günther 1861:306; Regan 1908, 1924; Starks 1908; Goodrich 1909:475–477; Jordan 1923; Greenwood et al. 1966; McAllister 1968; J. S. Nelson 2006). Molecular phylogenetic analyses consistently resolve Lampriformes as monophyletic to the exclusion of Stylephorus, which is resolved as the sister lineage of all other Gadiformes (Miya et al. 2007; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; Near et al. 2013; Alfaro et al. 2018; Hughes et al. 2018; Ghezelayagh et al. 2022). Morphological phylogenetic analyses aimed at relationships among lineages of Acanthomorpha are congruent with molecular phylogenies in resolving Lampriformes and Stylephorus as distantly related (Davesne et al. 2016).

  • Composition. There are currently 30 living species of Lampriformes (Fricke et al. 2023) classified in Lampris, Lophotidae, Radiicephalus, Regalecidae, and Veliferidae. Fossil taxa of Lampriformes include the species of VeliferidaeVeronavelifer sorbini; the pan-veliferids †Palaeocentrotus boeggildi, †Turkmene finitimus, and †Danatinia casca (Bannikov 1990, 1999, 2014a); the species of LophotidaeBabelichthys olneyi (Davesne 2017); the pan-lophotids †Protolophotus elami, †Eolophotes lenis, and †Oligolophotes fragosus (Walters 1957; Bannikov 1999; Davesne 2017); and the pan-lamprid †Megalampris keyesi (Gottfried et al. 2006). Details of the ages and locations for the fossil taxa are given in Appendix 1. In the last 10 years, four new living species of Lampriformes have been described (Underkoffler et al. 2018; Koeda and Ho 2019; Fricke et al. 2023), comprising 13.3% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Lampriformes include (1) second ural centrum free from fused first ural and preural centra and fused posteriorly to upper hypural plate (Patterson 1968; Wiley and Johnson 2010; Davesne et al. 2014, 2016; Delbarre et al. 2016; Cantalice et al. 2021), (2) anterior palatine process and anterior palatomaxillary ligament absent (Olney et al. 1993; Wiley and Johnson 2010; Davesne et al. 2014), (3) mesethmoid posterior to lateral ethmoids (Olney et al. 1993; Wiley and Johnson 2010), (4) elongate ascending processes of premaxillae and large rostral cartilage insert into frontal vault or cradle (Olney et al. 1993; Wiley and Johnson 2010; Davesne et al. 2014, 2016; Cantalice et al. 2021), (5) first dorsal fin pterygiophore inserts anterior to first neural spine (Olney et al. 1993; Wiley and Johnson 2010; Davesne et al. 2014, 2016; Cantalice et al. 2021), (6) postcleithrum composed of a single bone (Otero and Gayet 1996; Davesne et al. 2014, 2016; Delbarre et al. 2016; Cantalice et al. 2021), (7) premaxillary free of dentition (Delbarre et al. 2016), (8) dentary free of dentition (Delbarre et al. 2016), (9) endopterygoid free of dentition (Delbarre et al. 2016), and (10) condylar articulation between anterior ceratohyal and ventral hypohyal (Davesne et al. 2016; Cantalice et al. 2021).

  • Synonyms. Allotriognathi is an ambiguous (Regan 1907b:638–640; Garstang 1931:259) and a partial (Jordan 1923:165–166) synonym of Lampriformes. Atelaxia (Starks 1908:1) is a partial synonym of Lampriformes. Lampridiformes (Goodrich 1909:475–477; Walters and Fitch 1960:442; Greenwood et al. 1966:398; McAllister 1968:106–108; J. S. Nelson 1976:179–180; Lauder and Liem 1983:166; Olney et al. 1993:137; Springer and Johnson 2004:80–81; Wiley and Johnson 2010:127, 147), Lampridacea (Wiley and Johnson 2010:127, 147), Lamprimorpha (J. S. Nelson et al. 2016:280), and Lampripterygii (Betancur-R et al. 2017:20) are ambiguous synonyms of Lampriformes.

  • Comments. Lampriformes is the group name most frequently applied to the clade as defined here in several classifications of acanthomorphs (Davis et al. 2016; Betancur-R et al. 2017; Dornburg and Near 2021; Ghezelayagh et al. 2022).

  • The earliest fossil taxa of Lampriformes include †Danatinia casca and †Turkmene finitimus from the Ypresian (56.0–48.1 Ma) of Turkmenistan (Bannikov 1999). Bayesian relaxed molecular clock analyses of Lampriformes result in an average posterior crown age estimate of 58.1 million years ago, with the credible interval ranging between 55.8 and 69.7 million years ago (Ghezelayagh et al. 2022).

  • img-z93-6_03.gif

    Paracanthopterygii P. H. Greenwood, D. E. Rosen, S. H. Weitzman, and G. S. Myers 1966:352, 396–397
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Percopsis omiscomaycus (Walbaum 1792) (Percopsiformes) and Gadus morhua Linnaeus 1758 (Gadiformes). This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek παρά (p̍æɹә) meaning beside, ἇκανθα (æk̍ænθә) meaning thorn or spine, and πτερὀν (t̍εɹαːn) meaning fin or wing.

  • Registration number. 933.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of 989 ultraconserved element (UCE) loci (Ghezelayagh et al. 2022, fig. S1). Phylogenetic relationships of the living lineages and fossil taxa of Paracanthopterygii are presented in Figure 13. Placements of the fossil taxa in the phylogeny are on the basis of inferences from morphology (Tyler and Santini 2005; Alvarado-Ortega and Than-Marchese 2012; Murray and Wilson 2014; Davesne et al. 2016, 2017; Cantalice et al. 2021; Schrøder et al. 2022).

  • Phylogenetics. Paracanthopterygii was first delimited as a named group in Greenwood et al. (1966). Among teleosts there is no other taxonomic group that has had a more fluid history of hypotheses aimed at its composition (Rosen and Patterson 1969; Patterson and Rosen 1989; A. C. Gill 1996; T. Grande et al. 2013). The varied delimitations of Paracanthopterygii before the advent of molecular phylogenetics included Myctophiformes (Fraser 1972) and the percomorphs Ophidiiformes, Batrachoididae, Gobiesocoidei, Lophioidei, and Zoarcoidei (Rosen and Patterson 1969; Fraser 1972; Lauder and Liem 1982; Patterson and Rosen 1989). All of the premolecular delimitations of Paracanthopterygii excluded Zeiformes because they were considered a lineage of Acanthopterygii (Greenwood et al. 1966; Rosen 1984; Patterson and Rosen 1989; G. D. Johnson and Patterson 1993), despite inferences from morphology that argued for common ancestry of zeiforms and paracanthopterygians (M. Gaudant 1979; Gayet 1980b).

  • The delimitation of Paracanthopterygii that includes Gadiformes, Percopsiformes, Polymixia, and Zeiformes was first proposed as a result of phylogenetic analyses of whole mtDNA genomes (Miya et al. 2003, 2005), and supported in subsequent molecular studies (W. L. Smith and Wheeler 2006; B. Li et al. 2009; T. Grande et al. 2013; W.-J. Chen Santini, et al. 2014; Malmstrøm et al. 2016; Alfaro et al. 2018; Hughes et al. 2018; Musilova et al. 2019; Roth et al. 2020; Roa-Varón et al. 2021; Ghezelayagh et al. 2022; Mu et al. 2022; J.-F. Wang et al. 2023) as well as a phylogenetic analysis of discretely coded morphological characters (Davesne et al. 2016). A number of molecular phylogenetic analyses do not resolve Paracanthopterygii as monophyletic (Wiley et al. 2000; Holcroft 2004; Sparks et al. 2005; Dettaï and Lecointre 2008; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; Betancur-R et al. 2017; Near et al. 2013; Davis et al. 2016; Smith et al. 2016), but these studies are either on the basis of relatively small DNA sequence datasets or result in phylogenies with low support at nodes reflecting paracanthopterygian paraphyly.

  • Long classified in Lampriformes (Olney et al. 1993), Stylephorus chordatus is consistently resolved in molecular phylogenies as nested within Paracanthopterygii as the sister lineage of all other Gadiformes (Miya et al. 2007; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; Near et al. 2013; Malmstrøm et al. 2016, 2017; Alfaro et al. 2018; T. Grande et al. 2018; Hughes et al. 2018; Musilova et al. 2019; Roth et al. 2020; Ghezelayagh et al. 2022; J.-F. Wang et al. 2023). Within Paracanthopterygii, the results of phylogenetic analyses differ, with molecular and morphological studies resolving Polymixia and Percopsiformes as sister lineages (W.-J. Chen et al. 2003; Miya et al. 2005, 2007; W. L. Smith and Wheeler 2006; Dillman et al. 2011; Alvarado-Ortega and Than-Marchese 2012; Murray and Wilson 2014; Malmstrøm et al. 2016; Alfaro et al. 2018; Musilova et al. 2019; Roth et al. 2020; Cantalice et al. 2021; Ghezelayagh et al. 2022; J.-F. Wang et al. 2023), but other molecular studies resolving Polymixia as the sister lineage of all other paracanthopterygians (T. Grande et al. 2013; W.-J. Chen, Santini, et al. 2014; Hughes et al. 2018; Roa-Varón et al. 2021). Bayesian concordance factors estimated using UCE data find the hypothesis that Polymixia and Percopsiformes are sister lineages is supported by the greatest proportion of sampled loci, and the phylogeny that depicts Polymixia as the sister lineage of all other Paracanthopterygii is identified as less optimal (Ghezelayagh et al. 2022). Phylogenetic analyses of morphological datasets provide resolution for several fossil lineages of Paracanthopterygii (Murray and Wilson 1999; Tyler and Santini 2005; Alvarado-Ortega and Than-Marchese 2012; Murray and Wilson 2014; Davesne et al. 2016, 2017; Cantalice et al. 2021; Schrøder et al. 2022).

  • Composition. Paracanthopterygii currently includes 681 species (Fricke et al. 2023), classified in Gadiformes, Percopsiformes, Polymixia, and Zeiformes. Fossil lineages include the pan-polymixiid †Polyspinatus (Schrøder et al. 2022), the pan-percopsiforms †Sphenocephalidae and †Omosomopsis (Patterson 1964; M. Gaudant 1978a; Murray and Wilson 1999; Newbrey et al. 2013; Davesne et al. 2016; Cantalice et al. 2021), and the pan-zeiforms †Archaeozeus, †Bajaichthys, and †Protozeus (Tyler and Santini 2005; Davesne et al. 2017). Details of the ages and locations for the fossil taxa are given in Appendix 1. Over the past 10 years, 35 new species of Paracanthopterygii have been described (Fricke et al. 2023), comprising 5.1% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Paracanthopterygii include (1) presence of a full-length spine on dorsal surface of preural centrum 2 (Borden et al. 2013; T. Grande et al. 2013), (2) insertion sites of interradials on principal caudal and other rays (Borden et al. 2013), (3) first dorsal pterygiophore inserts posterior to neural spine 4 (Davesne et al. 2016; Cantalice et al. 2021), (4) no contact of pelvic girdle posterior to pectoral girdle (Davesne et al. 2016; Cantalice et al. 2021), and (5) base of pelvic fin spine asymmetrical (Cantalice et al. 2021).

  • Synonyms. Paracanthomorphacea (Betancur-R, Broughton, et al. 2013:12–13) is a partial synonym of Paracanthopterygii.

  • Comments. A consistent delimitation of Paracanthopterygii that includes Gadiformes, Percopsiformes, Polymixia, and Zeiformes in morphological and molecular studies is an important development in the resolution of phylogenetic relationships within Acanthomorpha. Remaining issues in the phylogenetics of Paracanthopterygii include the relationships of Percopsiformes and Polymixia and the resolution of the Cretaceous fossil lineages †Berycopsis, †Berycopsia, †Dalmatichthys, †Homonotichthys, and †Omosoma long classified with Polymixia in Polymixiiformes (Patterson 1964, 1993; Radovcic 1975; Bannikov and Bacchia 2005; Murray and Cumbaa 2013; Newbrey et al. 2013; Friedman et al. 2016).

  • The earliest fossils of Paracanthopterygii all date to the Cenomanian (100.5–93.9 Ma), including the species of †Sphenocephalidae, †Xenyllion zonensis from Canada, and the pan-percopsiform †Omosomopsis simum from Morocco (Otero and Gayet 1995; M. V. H. Wilson and Murray 1996; Newbrey et al. 2013; Murray and Wilson 2014; Davesne et al. 2016; Cantalice et al. 2021). Bayesian relaxed molecular clock analyses of Paracanthopterygii result in an average posterior crown age estimate of 120.7 million years ago, with the credible interval ranging between 101.9 and 135.0 million years ago (Ghezelayagh et al. 2022).

  • img-z96-5_03.gif

    FIGURE 13.

    Phylogenetic relationships of the major living lineages and fossil taxa of Paracanthopterygii, Percopsiformes, Zeiformes, Gadiformes, and Gadoidei. Filled circles identify the common ancestor of clades with formal names defined in the clade accounts. Open circles highlight clades with informal group names. Fossil lineages are indicated with a dagger (†). Details of the fossil taxa are presented in Appendix 1.

    img-z94-1_03.jpg

    Percopsiformes L. S. Berg 1937:1279
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Percopsis omiscomaycus (Walbaum 1792), Aphredoderus sayanus (Gilliams 1824), and Chologaster cornuta Agassiz 1853. This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek πέρκη (pˈke͡I) meaning perch, specifically the freshwater European Perch, Perca fluviatilis or the marine Painted Comber, Serranus scriba (D. W. Thompson 1947:194–197), and ὂΨις (ˈαːpsIs) meaning a vision or apparition. The suffix is from the Latin forma meaning form, figure, or appearance.

  • Registration number. 934.

  • Reference phylogeny. A phylogeny inferred using DNA sequences from one mtDNA gene and nine nuclear genes (Niemiller et al. 2013, fig. 1). Phylogenetic relationships of the living and fossil lineages of Percopsiformes are presented in Figure 13. The placements of fossil taxa in the phylogeny are on the basis of several phylogenetic studies (Murray and Wilson 1999; Borden et al. 2013; T. Grande et al. 2013; Guinot and Cavin 2018; Murray et al. 2020).

  • Phylogenetics. The delimitation of Percopsiformes presented here is consistent with several pre-Hennigian phylogenetic studies based on morphology (Rosen 1962; Gosline 1963a; Greenwood et al. 1966; McAllister 1968; Rosen and Patterson 1969). Phylogenetic analyses of morphological characters are incongruent, with some studies not supporting the monophyly of Percopsiformes (Rosen 1985; Patterson and Rosen 1989; Murray and Wilson 1999; Murray et al. 2020), but other analyses resolving Percopsiformes as a clade (Springer and Orrell 2004; Davesne et al. 2016; Cantalice et al. 2021). In contrast to the lack of agreement among morphological studies, molecular phylogenetic analyses consistently resolve Percopsiformes as monophyletic with Percopsis (troutperches) as the sister lineage of a clade containing Amblyopsidae (cavefishes) and Aphredoderus sayanus (Pirate Perch) (W. L. Smith and Wheeler 2006; Dillman et al. 2011; Near, Eytan, et al. 2012; T. Grande et al. 2013; Near et al. 2013; Davis et al. 2016; Smith et al. 2016; Betancur-R et al. 2017; T. Grande et al. 2018; Ghezelayagh et al. 2022). The presumed monophyly of Percopsiformes was the basis for the selection of Percopsis and Aphredoderus sayanus as the sole outgroups in morphological and molecular phylogenetic analyses of Amblyopsidae (Niemiller et al. 2013; Armbruster et al. 2016; Hart et al. 2020).

  • Composition. There are currently 13 living species of Percopsiformes that include Aphredoderus sayanus and species classified in Percopsis and Amblyopsidae (Poly 2004a, 2004b; Poly and Proudlove 2004; Fricke et al. 2023). Fossil taxa of Percopsiformes include †Lindoeichthys albertensis from the Maastrichtian Scollard Formation, Canada (Murray et al. 2020), †Mcconichthys longipinnis from the Danian Tullock Member, USA (L. Grande 1988), †Amphiplaga brachyptera and †Erismatopterus levatus from the Ypresian Green River Formation, USA (Cope 1871c, 1877a; L. Grande 1984), †Libotonius blakeburnensis from the Ypresian Blakeburn Mine, Canada (M. V. H. Wilson 1977), †Lateopisciculus turrifumosus and †Massamorichthys wilsoni from the Selandian–Thanetian Paskapoo Formation, Canada (Murray 1996; Murray and Wilson 1996), and †Tricophanes foliarum from the Priabonian Florissant, USA (Cope 1878; Meyer 2003:179). Details of the ages and locations for the fossil taxa are given in Appendix 1. In the last 10 years, a single new living species of Percopsiformes has been described (Chakrabarty et al. 2014; Fricke et al. 2023), comprising 8.3% of the living species diversity in the clade. Analyses of morphology and genomic data indicate that there are three additional species of Aphredoderus awaiting formal taxonomic description (Muller 2023).

  • Diagnostic apomorphies. Morphological apomorphies for Percopsiformes include (1) absence of postmaxillary process on premaxilla (Patterson and Rosen 1989; Murray and Wilson 1999; Davesne et al. 2016; Cantalice et al. 2021), (2) six branchiostegal rays (Murray and Wilson 1999), (3) presence of opercular dorsal projection that is anteriorly truncated or excavated (Murray and Wilson 1999), (4) transverses dorsales and obliqui dorsalis are combined and have a trapezoidal shape in dorsal view (Springer and Johnson 2004; Wiley and Johnson 2010), (5) obliquus dorsalis 4 extends posteriorly to insert on levator process of epibranchial 4 (Springer and Johnson 2004; Wiley and Johnson 2010), (6) two hypural plates do not contact any ural centra (Borden et al. 2013), (7) presence of a two-headed cranio-hyomandibular articulation (Davesne et al. 2016; Cantalice et al. 2021), (8) posterior and anterior ceratohyals sutured (Davesne et al. 2016; Cantalice et al. 2021), (9) metapterygoid contacts quadrate (Cantalice et al. 2021), and (10) condylar articulation between the anterior ceratohyal and ventral hypohyal (Cantalice et al. 2021).

  • Synonyms. Percopsacea (Wiley and Johnson 2010:147) and Percopsaria (Betancur-R et al. 2017:20) are ambiguous synonyms of Percopsiformes. Salmopercae (Goodrich 1909:425–426; Regan 1909a:79, 84–85, 1911b:294, 1929:305, 318) is a partial synonym of Percopsiformes.

  • Comments. Percopsiformes is the group name consistently applied to the clade as defined here (Rosen and Patterson 1969; Wiley and Johnson 2010; Davis et al. 2016; J. S. Nelson et al. 2016:287–289; Betancur-R et al. 2017; Dornburg and Near 2021; Ghezelayagh et al. 2022).

  • The earliest fossil Percopsiformes is †Lindoeichthys albertensis from Canada (Murray et al. 2020). Bayesian relaxed molecular clock analyses of Percopsiformes result in an average posterior crown age estimate of 53.5 million years ago, with the credible interval ranging between 40.1 and 72.4 million years ago (Ghezelayagh et al. 2022).

  • img-z97-8_03.gif

    Zeiformes L. S. Berg 1937:1279
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Zeus faber Linnaeus 1758, Cyttus australis (Richardson 1843), Cyttopsis rosea (Lowe 1843), and Macrurocyttus acanthopodus (Fowler 1934). This is a minimum-crown-clade definition.

  • Etymology. Zeus is the god of thunder and the sky in ancient Greek religion. The suffix is from the Latin forma meaning form, figure, or appearance.

  • Registration number. 940.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of three mtDNA regions and five nuclear genes (T. Grande et al. 2018, fig. 3). Phylogenetic relationships of the living lineages and fossil taxa of Zeiformes are presented in Figure 13. Placements of the fossil taxa in the phylogeny are on the basis of analyses of morphological characters (Tyler and Santini 2005; Davesne et al. 2017).

  • Phylogenetics. Prior to molecular phylogenetic analyses, Zeiformes was classified as a lineage of Acanthopterygii (Greenwood et al. 1966; Rosen 1984; G. D. Johnson and Patterson 1993). Molecular analyses consistently resolve Zeiformes and Gadiformes as sister lineages (Wiley et al. 2000; W.-J. Chen et al. 2003; Miya et al. 2003, 2005, 2007; Sparks et al. 2005; W. L. Smith and Wheeler 2006; Dettaï and Lecointre 2008; B. Li et al. 2009; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; T. Grande et al. 2013; Near et al. 2013; W.-J. Chen, Santini, et al. 2014; Davis et al. 2016; Malmstrøm et al. 2016; Smith et al. 2016; Betancur-R et al. 2017; Alfaro et al. 2018; Hughes et al. 2018; Roth et al. 2020; Roa-Varón et al. 2021; Ghezelayagh et al. 2022; Mu et al. 2022).

  • There are two sets of phylogenetic analyses of Zeiformes based on morphological characters that result in very different phylogenetic trees. A group of two morphological phylogenies work from the premise that Zeiformes are acanthopterygians and consequently use species of Beryciformes, Trachichthyiformes, Antigonia, Tetraodontoidei, Moronidae, and Capros aper as outgroups (Tyler et al. 2003; Tyler and Santini 2005). The other morphological phylogeny follows the inferences stemming from molecular phylogenetic analyses and uses species of Polymixia, Percopsiformes, and Gadiformes as outgroup taxa (T. Grande et al. 2018). Both sets of phylogenetic analyses resolve most of the major lineages (e.g., Cyttus [lookdown dories], Oreosomatidae [oreos], Parazenidae [smooth dories], Zeidae [dories], and Zeniontidae [armoreye dories]) of Zeiformes as monophyletic (Tyler et al. 2003; Tyler and Santini 2005; T. Grande et al. 2018), but the resolution of Macrurocyttus acanthopodus (Dwarf Dory) renders Grammicolepididae (tinselfishes) as paraphyletic in one of the studies (T. Grande et al. 2018). The two morphological phylogenies are completely incongruent with regard to the relationships among the major lineages of Zeiformes (Tyler et al. 2003; Tyler and Santini 2005; T. Grande et al. 2018), perhaps a result of using acanthopterygian rather than paracanthopterygian outgroups (T. Grande et al. 2018).

  • Relationships within Zeiformes inferred from a molecular phylogenetic analysis are not congruent with either of the morphological inferred phylogenies, but are more similar to the trees resulting from analyses using Paracanthopterygii as outgroups (T. Grande et al. 2018). In the molecular phylogeny, Zeidae is the sister lineage of all other Zeiformes, Zeniontidae is paraphyletic because Capromimus is resolved as the sister lineage of Oreosomatidae, and Grammicolepididae, Parazenidae, and Zenion are resolved as monophyletic. Relationships among the lineages of Zeiformes resolved in the molecular phylogeny are not strongly supported and are reasonably interpreted as a polytomy near the inferred common ancestor of the clade, which is indicative of a period of rapid lineage diversification early in the evolutionary history of Zeiformes (T. Grande et al. 2018). The enigmatic and infrequently encountered Macrurocyttus is not sampled in any molecular phylogeny, and analyses of combined molecular and morphological datasets resolve this lineage as a deeply branching sister lineage of all other Zeiformes (T. Grande et al. 2018).

  • Composition. There are currently 33 living species of Zeiformes classified in Cyttus, Grammicolepididae, Oreosomatidae, Parazenidae, Zeidae, and Zeniontidae (Fricke et al. 2023). Fossil taxa of Zeiformes include the pan-parazenid †Cretazeus and several species from the Oligocene and Miocene classified as Zeus and Zenopsis (Tyler et al. 2000, 2003; Tyler and Santini 2005; Santini et al. 2006). Details of the ages and locations for the fossil taxa are given in Appendix 1. In the last 10 years, a single new living species of Zeiformes has been described (Kai and Tashiro 2019; Fricke et al. 2023), comprising 3.0% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Zeiformes include (1) distal portions of proximal-middle dorsal fin radials laterally expanded (G. D. Johnson and Patterson 1993; Wiley and Johnson 2010), (2) distal radials of spinous portion of dorsal fin absent or reduced to minuscule cartilaginous or incompletely ossified elements (G. D. Johnson and Patterson 1993; Wiley and Johnson 2010), (3) palatine has a mobile articulation with ectopterygoid that is dorsally truncated (G. D. Johnson and Patterson 1993; Tyler et al. 2003; Wiley and Johnson 2010; T. Grande et al. 2018), (4) reduced metapterygoid (G. D. Johnson and Patterson 1993; Tyler et al. 2003; Wiley and Johnson 2010; T. Grande et al. 2013, 2018), (5) flexible articulations on anterior vertebral centra; if ribs are present they are never anterior to fourth vertebra (G. D. Johnson and Patterson 1993; Wiley and Johnson 2010), (6) pharyngobranchials 2 and 3 with upright columnar processes (G. D. Johnson and Patterson 1993; Wiley and Johnson 2010), (7) absence of pharyngobranchial 4 and upper pharyngeal tooth plate (G. D. Johnson and Patterson 1993; Wiley and Johnson 2010; T. Grande et al. 2018), (8) area below frontals from ethmoid cartilage to parasphenoid with a continuous medial cartilage (G. D. Johnson and Patterson 1993; Tyler et al. 2003; Wiley and Johnson 2010), (9) second pleural centrum with full neural spine (G. D. Johnson and Patterson 1993; Wiley and Johnson 2010), (10) proximally truncated parhypural (G. D. Johnson and Patterson 1993; Tyler et al. 2003; Wiley and Johnson 2010), (11) presence of 3.5 gills and seven hemibranchs (Tyler et al. 2003), (12) dorsal-, anal-, and pectoral-fin rays unbranched (Tyler et al. 2003; Wiley and Johnson 2010), (13) absence of uncinate process on epibranchial 1 (Tyler et al. 2003; T. Grande et al. 2018), (14) absence of open gill slit between branchial arches 4 and 5 (Tyler et al. 2003; T. Grande et al. 2018), (15) fusion of hypurals 1–2 and 3–4; both elements fused to centrum (Tyler et al. 2003; Wiley and Johnson 2010; T. Grande et al. 2018), (16) first proximal radial of dorsal fin and first neural arch and spine in contact (T. Grande et al. 2013), (17) principal caudal-fin rays the only insertion site of caudal fin interradialis muscle (Borden et al. 2013), presence of single procurrent caudal-fin ray (T. Grande et al. 2018), and (18) 12 principal caudal-fin rays (T. Grande et al. 2018).

  • Synonyms. Zeoidei (Regan 1909a:80; Jordan 1923:171), Zeomorphi (Regan 1910a:481–482; Rosen 1984:44; Zehren 1987, fig. 1), Zeacea (Wiley and Johnson 2010:150), and Zeiariae (Betancur-R et al. 2017:20) are ambiguous synonyms of Zeiformes.

  • Comments. Since the mid-20th century Zeiformes was consistently applied as the group name for the clade defined above and was selected as the clade name over its synonyms because it is the name most frequently applied to a taxon approximating the named clade (e.g., Greenwood et al. 1966; Wiley et al. 2000; Borden et al. 2013; T. Grande et al. 2013; Davis et al. 2016; Betancur-R et al. 2017; Ghezelayagh et al. 2022).

  • The earliest fossil Zeiformes is †Cretazeus rinaldii from the Campanian-Maastrichtian of Italy (Appendix 1; Tyler et al. 2000). Bayesian relaxed molecular clock analyses of Zeiformes result in an average posterior crown age estimate of 50.0 million years ago, with the credible interval ranging between 37.3 and 72.0 million years ago (Ghezelayagh et al. 2022).

  • img-z99-7_03.gif

    Gadiformes P. Bleeker 1859:xxvi

  • Definition. The least inclusive crown clade that contains Stylephorus chordatus Shaw 1791 and Gadus morhua Linnaeus 1758. This is a minimum-crown-clade definition, but the clade is not defined using the PhyloCode.

  • Etymology. From the ancient Greek γάδoϛ (ɡˈ̍αːdo͡Ʊz), which was a name applied to the European Hake, Merluccius merluccius (D. W. Thompson 1947:38). The suffix is from the Latin forma meaning form, figure, or appearance.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of 989 ultraconserved element loci (Ghezelayagh et al. 2022, fig. S1). Phylogenetic relationships of the major lineages of Gadiformes are presented in Figure 13.

  • Phylogenetics. Historically, Stylephorus chordatus was classified in Lampriformes (Regan 1908; Olney et al. 1993; J. S. Nelson 2006:228–229) and Gadoidei was hypothesized to be closely related to Batrachoididae and Lophioidei (Patterson and Rosen 1989). A more recent phylogenetic analysis of Acanthomorpha based on morphological characters resolves Gadoidei as the sister lineage to a clade containing Stylephorus and Zeiformes (Davesne et al. 2016). On the other hand, molecular phylogenetic analyses consistently resolve Stylephorus and Gadoidei as a monophyletic group (Miya et al. 2007; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; Near et al. 2013; Davis et al. 2016; Smith et al. 2016; Alfaro et al. 2018; T. Grande et al. 2018; Hughes et al. 2018; Roth et al. 2020; Ghezelayagh et al. 2022; Mu et al. 2022; J.-F. Wang et al. 2023).

  • Composition. There are currently 625 living species of Gadiformes (Fricke et al. 2023) that include Stylephorus chordatus and species classified in Gadoidei. Over the past 10 years, 32 new species of Gadiformes have been described (Cohen et al. 1990; Fricke et al. 2023), comprising 5.1% of the species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Gadiformes include (1) levator arcus palatini lies lateral to section A2 of adductor mandibulae (T. Grande et al. 2013), (2) interradialis located only between caudal-fin rays (Borden et al. 2013), (3) hypochondral longtudinalis absent (Borden et al. 2013), and (4) most ural centra and pleural centra 2–4 exposed after removal of body musculature (Borden et al. 2013).

  • Synonyms.Gadariae(Betancur-Retal.2017:20) is an ambiguous synonym of Gadiformes.

  • Comments. Since the first phylogenetic analysis that resolved Stylephorus and Gadoidei as a monophyletic group (Miya et al. 2007), the substantial molecular evidence is supported by the discovery of morphological apomorphies providing confidence to the resolution of a more inclusive Gadiformes that includes Stylephorus (Borden et al. 2013). Bayesian relaxed molecular clock analyses of Gadiformes result in an average posterior crown age estimate of 88.4 million years ago, with the credible interval ranging between 72.9 and 105.4 million years ago (Ghezelayagh et al. 2022).

  • img-z100-11_03.gif

    Gadoidei L. J. F. J. Fitzinger 1832:331

  • Definition. The least inclusive crown clade that contains Bregmaceros cantori Milliken and Houde 1984, Gadus morhua Linnaeus 1758, and Macruronus novaezelandiae (Hector 1871). This is a minimum-crown-clade definition, but the clade is not defined using the PhyloCode.

  • Etymology. From the ancient Greek γάδoϛ (ɡˈ̍αːdo͡Ʊz), which was a name applied to the European Hake, Merluccius merluccius (D. W. Thompson 1947:38).

  • Reference phylogeny. A phylogeny inferred from DNA sequences of 14,208 exons (Roa-Varón et al. 2021, fig. 4). Phylogenetic relationships of the major lineages of Gadoidei are presented in Figure 13.

  • Phylogenetics. Precladistic studies of relationships within Gadoidei concluded that Melanonus (pelagic cods) (Marshall 1965, 1966; Marshall and Cohen 1973) or Muraenolepididae (eel cods) (Rosen and Patterson 1969; Cohen 1984) represented the lineage with the least derived morphology in the clade. A theme in the study of gadoid morphology is that lineages are characterized by combinations of ancestral and derived character states (Rosen and Patterson 1969; Cohen 1984; Okamura 1989; Endo 2002). The heterogeneous nature of gadoid morphology is reflected in the dramatically minimal congruence among the more than 10 morphological phylogenies that examined a wide range of osteological, myological, and otolith characters (J. R. Dunn 1989; Howes 1989, 1991a, 1993; Iwamoto 1989; Markle 1989; Nolf and Steurbaut 1989; Okamura 1989; Howes 1990; Siebert 1990; Endo 2002; Teletchea et al. 2006; Grand et al. 2014). Heterochronic evolution has been invoked to explain the characteristic mosaic of ancestral and derived morphology in Gadoidei (Endo 2002), highlighting the potential challenges of using morphological characters to resolve phylogenetic relationships within the clade.

  • The first set of molecular phylogenetic studies of Gadoidei utilized data from Sanger-sequenced mitochondrial and nuclear genes and resulted in phylogenies with relatively poor node support (Møller et al. 2002; Bakke and Johansen 2005; Teletchea et al. 2006; von der Heyden and Matthee 2008; Roa-Varón and Ortí 2009; Betancur-R et al. 2017), limiting the ability of these analyses to resolve the deepest nodes in the gadoid phylogeny. Despite the challenge of limited resolution, the first group of gadoid molecular phylogenies demonstrated that previous delimitations of Merlucciidae (merluccid hakes) (Inada 1989; Cohen et al. 1990; Lloris et al. 2005) are not monophyletic, motivating the recognition of the monogeneric taxonomic families Macruronidae (southern grenadiers), Lyconidae (Atlantic hakes), and Steindachneriidae (Steindachneria argentea, Luminous Hake) (von der Heyden and Matthee 2008; Roa-Varón and Ortí 2009).

  • Next-generation phylogenomic analyses vary in the level of resolution and node support, but all result in phylogenies in which Bregmaceros (codlets) is placed as the sister lineage of all other Gadoidei (Malmstrøm et al. 2016; Hughes et al. 2018; Han et al. 2021; Roa-Varón et al. 2021; Ghezelayagh et al. 2022). The phylogenetic resolution of Bregmaceros is consistent with the observation that this lineage is “fundamentally different myologically and osteologically from other gadoids” (Rosen and Patterson 1969:427). The phylogenomic analyses agree with several earlier molecular studies in resolving Gadidae (cods), Lotidae (burbots), and Phycidae (hakes), all previously classified as Gadidae, as a monophyletic group (von der Heyden and Matthee 2008; Roa-Varón and Ortí 2009; Betancur-R et al. 2017). There is appreciable congruence among the trees generated from phylogenomic analyses but there is disagreement regarding the relationships of Muraenolepididae, Trachyrincidae (armored grenadiers), Melanonus, and Merlucciidae (Malmstrøm et al. 2016; Hughes et al. 2018; Han et al. 2021; Roa-Varón et al. 2021; Ghezelayagh et al. 2022).

  • Composition. There are currently 624 living species of Gadoidei that include Raniceps raninus (Tadpole Fish), Steindachneria argentea, and species classified in Bathygadidae (rattails), Bregmaceros, Euclichthys (eucla cods), Gadidae, Gaidropsaridae (rocklings), Lotidae, Lyconus, Macrouridae (grenadiers), Macruronus (blue grenadiers), Melanonus, Merlucciidae, Moridae (morid cods), Muraenolepididae, Phycidae, and Trachyrincidae (Cohen et al. 1990; Lloris et al. 2005; Roa-Varón et al. 2021; Fricke et al. 2023). Over the past 10 years, 32 new species of Gadoidei have been described (Fricke et al. 2023), comprising 5.1% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Gadoidei include (1) presence of X and Y bones in caudal skeleton (Cohen 1984; Fahay and Markle 1984; Markle 1989; Patterson and Rosen 1989), (2) first neural spine joined to occipital crest (Cohen 1984; Patterson and Rosen 1989), (3) larvae with anus that exits through the finfold (Fahay and Markle 1984; Markle 1989), (4) absence of ribs or epipleurals on vertebrae 1 and 2 (Markle 1989; Patterson and Rosen 1989; Howes 1993), (5) scapular foramen located between scapula and coracoid (Markle 1989; Patterson and Rosen 1989; Howes 1993; Endo 2002; Wiley and Johnson 2010), (6) notch in the front of the prootic is exit point for trigeminal and facial nerves from braincase, with absence of lateral commissure or trigeminofacial chamber (Patterson and Rosen 1989), (7) anal and dorsal fins with three fin rays per segment (Patterson and Rosen 1989), (8) head canals with 33 neuromasts (Patterson and Rosen 1989), (9) presence of three struts on pharyngobranchial 3 (Markle 1989), (10) otolith with pince-nezshaped sulcus and lateral collicular (Nolf and Steurbaut 1989; Endo 2002; Wiley and Johnson 2010), (11) absence of jugular foramen (Howes 1991a, 1993), (12) attrition of anterior border of lateral face of hyomandibular, exposing pathway of the hyoid branch of the facial nerve (Howes 1993), (13) dorsal hyomandibular with a single condyle (Endo 2002; Wiley and Johnson 2010), (14) basihyal absent (Endo 2002; Wiley and Johnson 2010; T. Grande et al. 2013), (15) flexor dorsalis and flexor ventralis separate with some bundles serving a single ray compounded (Borden et al. 2013), (16) flexor dorsalis and flexor dorsalis superior are a single muscle mass (Borden et al. 2013), and (17) flexor ventralis and flexor ventralis inferior are a single muscle mass (Borden et al. 2013).

  • Synonyms. Gadiformes (e.g., Cohen 1984; Patterson and Rosen 1989:13–19; Cohen et al. 1990, fig. 1; A. C. Gill and Mooi 2002, tbl. 2.3; Wiley and Johnson 2010:148–149; J. S. Nelson et al. 2016:293–302; Betancur-R et al. 2017:20) is an ambiguous synonym of Gadoidei.

  • Comments. The application of phylogenetic systematics has contributed to a flux in the classification of lineages that comprise Gadoidei since the mid-1980s (Cohen 1984; Markle 1989; Endo 2002; Roa-Varón and Ortí 2009; Roa-Varón et al. 2021). A more recent Linnaean classification of gadoids has an abundance of redundant group names as it recognizes 17 families of which seven comprise a single genus and five suborders of which three contain a single family (Roa-Varón et al. 2021).

  • The early fossil record of Gadoidei is dominated by otoliths (Kriwet and Hecht 2008). The earliest otolith fossils of Gadoidei include †Rhinocephalus cretaceus and †Archaemacruroides vanknippenbergi from the Maastrichtian (72.2–66.0 Ma) of Belgium and Netherlands (Schwarzhans and Jagt 2021), and †Dakotaichthys hogansoni, †Palaeogadus weltoni, and †Archaemacruroides bratishkoi from the Maastrichtian of Texas, USA (Schwarzhans and Stringer 2020). Bayesian relaxed molecular clock analyses of Gadoidei result in an average posterior crown age estimate of 77.0 million years ago, with the credible interval ranging between 61.5 and 98.2 million years ago (Ghezelayagh et al. 2022).

  • img-z102-6_03.gif

    Acanthopterygii P. Artedi 1738:26
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Diretmus argenteus Johnson 1864 (Trachichthyiformes), Beryx decadactylus Cuvier 1829 in Cuvier and Valenciennes (1829b) (Beryciformes), Holocentrus rufus (Walbaum 1792) (Beryciformes), Carapus bermudensis (Jones 1874) (Ophidiiformes), and Micropterus salmoides (Lacépède 1802) (Centrarchiformes), but not Percopsis omiscomaycus (Walbaum 1792) (Percopsiformes) nor Gadus morhua Linnaeus 1758 (Gadiformes). This is a minimum-crown-clade definition with external specifiers.

  • Etymology. From the ancient Greek ἇκανθα (æk̍ænθә) meaning thorn or spine and πτερόν (t̍εɹαːn) meaning feather, wing, or any winged animal.

  • Registration number. 943.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of 989 ultraconserved element (UCE) loci (Ghezelayagh et al. 2022, figs. S2–S25). Phylogenetic relationships of the major lineages of Acanthopterygii are presented in Figures 2 and 14. The placements of the pan-trachichthyiforms †Judeoberyx and †Lissoberyx, and the pan-percomorph †Pepemkay in the phylogeny are on the basis of inferences from morphological studies (Moore 1993a, 1993b; Patterson 1993; Friedman 2009; Cantalice et al. 2021).

  • Phylogenetics. Morphological and molecular phylogenetic analyses consistently support the monophyly of Acanthopterygii (Miya et al. 2003, 2005; W. L. Smith and Wheeler 2006; Alfaro, Santini, et al. 2009; Santini et al. 2009; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; T. Grande et al. 2013; Near et al. 2013; W.-J. Chen, Santini, et al. 2014; Davesne et al. 2016; Davis et al. 2016; Malmstrøm et al. 2016, 2017; Smith et al. 2016; Betancur-R et al. 2017; Hughes et al. 2018; Musilova et al. 2019; Roth et al. 2020; Cantalice et al. 2021; Ghezelayagh et al. 2022; Mu et al. 2022; J.-F. Wang et al. 2023). However, earlier morphological studies nested the paracanthopterygian Zeiformes in Acanthopterygii (Stiassny and Moore 1992; G. D. Johnson and Patterson 1993).

  • Phylogenetic analyses of Acanthopterygii differ on the relationships among Trachichthyiformes, Beryciformes, and Percomorpha. Morphological phylogenetic studies led to delimitations of Trachichthyiformes and Beryciformes that differ from current classifications and deviate from one another primarily in the relationships of Holocentridae and Berycidae (Rosen 1973; Stiassny and Moore 1992; G. D. Johnson and Patterson 1993; Moore 1993b). Molecular studies result in four sets of phylogenies of Acanthopterygii: a clade containing Beryciformes and Trachichthyiformes that is the sister lineage of Percomorpha (W. L. Smith and Wheeler 2006; Alfaro, Santini, et al. 2009; Santini et al. 2009; Near, Eytan, et al. 2012; T. Grande et al. 2013; Near et al. 2013; Malmstrøm et al. 2017; Mu et al. 2022), Beryciformes (excluding Holocentridae) and Trachichthyiformes as a monophyletic group that is the sister lineage of Holocentridae (Near et al. 2013; Rabosky et al. 2018; J.-F. Wang et al. 2023), Beryciformes (excluding Holocentridae) and Trachichthyiformes as a monophyletic group that is the sister lineage of a clade containing Holocentridae and Percomorpha (Betancur-R, Broughton, et al. 2013; Smith et al. 2016; Betancur-R et al. 2017), and Trachichthyiformes as the sister lineage of a clade containing Beryciformes and Percomorpha (Figures 2 and 14; Miya et al. 2003, 2005; Thacker 2009; W.-J. Chen, Santini, et al. 2014; Malmstrøm et al. 2016; Dornburg et al. 2017; Hughes et al. 2018, fig. S2; Musilova et al. 2019; Roth et al. 2020; Ghezelayagh et al. 2022).

  • Morphological studies aimed at resolving the relationships of several Cretaceous acanthomorph fossil lineages place Hoplostethus (Trachichthyiformes) as the sister lineage of a clade containing Sargocentron (Beryciformes) and Percomorpha, but these studies are limited in taxon sampling and do not test the monophyly of Trachichthyiformes or Beryciformes (Davesne et al. 2016; Cantalice et al. 2021). Bayesian concordance factors estimated in a phylogenomic analysis of UCE loci find the hypothesis that Beryciformes and Percomorpha are sister lineages is supported by the greatest proportion of sampled loci, and phylogenies that depict either Holocentridae or a clade containing Beryciformes and Trachichthyiformes as the sister lineage of Percomorpha are less optimal (Ghezelayagh et al. 2022).

  • Composition. There are currently more than 19,185 living species of Acanthopterygii classified in Trachichthyiformes, Beryciformes, and Percomorpha. Fossil lineages include the pan-trachichthyiforms †Judeoberyx and †Lissoberyx (Patterson 1967; Gayet 1980b), and the pan-percomorph †Pepemkay (Alvarado-Ortega and Than-Marchese 2013). Details of the ages and locations of fossil taxa are presented in Appendix 1. Over the past 10 years, 1,641 new living species of Acanthopterygii have been described (Fricke et al. 2023), comprising 8.6% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Acanthopterygii include (1) retractor dorsalis muscle inserts primarily on pharyngobranchial 3 (Rosen 1973), (2) reduction of surface of epibranchial 4 and enlargement of epibranchials 2 and 3, which form the primary support for the upper pharyngeal jaw dentition (Rosen 1973), (3) presence of two hyomandibular articulation facets (Davesne et al. 2016), (4) proximal insertion of Baudelot's ligament onto the basioccipital (Davesne et al. 2016), and (5) presence of an antero-median pelvic process (Davesne et al. 2016).

  • Synonyms. Euacanthomorphacea (Betancur-R, Broughton, et al. 2013, app. 2) is an ambiguous synonym of Acanthopterygii. Euacanthopterygii (G. D. Johnson and Patterson 1993:607) is an approximate synonym of Acanthopterygii.

  • Comments. Classifications of Acanthomorpha differ in the application of the group name Acanthopterygii: (1) to the paraphyletic group that includes Zeiformes, Lampriformes, Trachichthyiformes, Beryciformes, and Percomorpha (Greenwood et al. 1966); (2) the likely paraphyletic group containing Lampriformes, Trachichthyiformes, Beryciformes, and Percomorpha (Davis et al. 2016); and (3) the clade containing Trachichthyiformes, Beryciformes, and Percomorpha as defined here (J. S. Nelson et al. 2016:302–303; Betancur-R et al. 2017; Hughes et al. 2018; Ghezelayagh et al. 2022). The name Acanthopterygii was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade.

  • The morphological characterization of Acanthopterygii was hampered by previous phylogenetic studies and resulting classifications that placed the acanthopterygian lineages Ophidiiformes, Batrachoididae, and Lophioidei into Paracanthopterygii and treated the paracanthopterygian Zeiformes as an acanthopterygian (Lauder and Liem 1983; J. S. Nelson 1984, 1994, 2006; Rosen 1984; Patterson and Rosen 1989; Stiassny and Moore 1992; G. D. Johnson and Patterson 1993). The concept of Acanthopterygii as limited to Trachichthyiformes, Beryciformes, and Percomorpha originated from many molecular phylogenetic analyses (e.g., Miya et al. 2003; Alfaro, Santini, et al. 2009; Near, Eytan, et al. 2012; W.-J. Chen, Santini, et al. 2014; Malmstrøm et al. 2016; Ghezelayagh et al. 2022) and is validated in phylogenetic analyses of morphological characters (Davesne et al. 2016; Cantalice et al. 2021).

  • The earliest acanthopterygian fossils date to the Cenomanian (100.5–93.9 Ma) (Patterson 1993; Friedman 2009, 2010; Murray 2016). Bayesian relaxed molecular clock analyses of Actinopterygii result in an average posterior age estimate of 137.4 million years ago, with the credible interval ranging between 129.1 and 147.3 million years ago (Ghezelayagh et al. 2022).

  • img-z105-6_03.gif

    FIGURE 14.

    Phylogenetic relationships of the major living lineages and fossil taxa of Acanthopterygii, Trachichthyiformes, Beryciformes, Berycoidei, Percomorpha, Ophidiiformes, Bythitoidei, Gobiiformes, Apogonoidei, Gobioidei, Ovalentaria, and Eupercaria. Filled circles identify the common ancestor of clades with formal names defined in the clade accounts. Open circles highlight clades with informal group names. Fossil lineages are indicated with a dagger (†). Details of the fossil taxa are presented in Appendix 1.

    img-z104-1_03.jpg

    Trachichthyiformes M. L. J. Stiassny and J. A. Moore 1992:212, figs. 14, 15, and 16
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Trachichthys australis Shaw 1799 in Shaw and Nodder (1799), Diretmus argenteus J. Y. Johnson 1864, and Aulotrachichthys prosthemius (Jordan and Fowler 1902), but not Beryx decadactylus Cuvier in Cuvier and Valenciennes (1829b) nor Holocentrus rufus (Walbaum 1792). This is a minimum-crown-clade definition with external specifiers.

  • Etymology. From the ancient Greek τρᾱχὐς (tɹˈ̍e͡Ikәs) meaning rough and ἰχθὐς (̍kIkθuːs) meaning fish. The suffix is from the Latin forma meaning form, figure, or appearance.

  • Registration number. 944.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of 989 ultraconserved element loci (Ghezelayagh et al. 2022, fig. S2). Although Trachichthys australis is not included in the reference phylogeny, it resolves in a clade with other species of Trachichthyidae in a phylogenetic analysis of morphological characters (Zehren 1979, figs. 4, 5). Phylogenetic relationships of the major lineages of Trachichthyiformes are presented in Figure 14.

  • Phylogenetics. Morphological analyses resolved the prephylogenetic delimitation of Beryciformes as paraphyletic relative to Zeiformes and Percomorpha (Stiassny and Moore 1992; G. D. Johnson and Patterson 1993). The relationships of these lineages differed among morphological phylogenetic analyses. One set of studies introduced Trachichthyiformes as a clade that includes Anomalopidae (flashlight fishes), Anoplogaster (fangtooths), Diretmidae (spinyfins), Monocentridae (pinecone fishes), Trachichthyidae (roughies), and all lineages delimited here as Beryciformes except for Berycidae (alfonsinos) and Holocentridae (squirrelfishes) (Stiassny and Moore 1992; Moore 1993b). In a different analysis of morphological characters, a clade Stephanoberyciformes was resolved that includes all lineages delimited here as Beryciformes to the exclusion of Berycidae and Holocentridae and a definition of Beryciformes that included what is delimited here as Trachichthyiformes with the addition of Berycidae and Holocentridae (G. D. Johnson and Patterson 1993).

  • The monophyly of Trachichthyiformes is supported in morphological (Zehren 1979; Moore 1993b; Baldwin and Johnson 1995; Konishi and Okiyama 1997) and molecular phylogenetic studies (Miya et al. 2003, 2005; T. Grande et al. 2013; Near et al. 2013; Davis et al. 2016; Betancur-R et al. 2017; Dornburg et al. 2017; Malmstrøm et al. 2017; Musilova et al. 2019; Ghedotti et al. 2021; Ghezelayagh et al. 2022; Mu et al. 2022). Phylogenetic relationships among lineages of Trachichthyiformes inferred from morphological and molecular data differ substantially. Morphological inferences resolve Anoplogaster and Diretmidae as a clade that is the sister lineage of all other Trachichthyiformes (Moore 1993b; Konishi and Okiyama 1997). Molecular phylogenies and analyses of combined molecular and morphological datasets consistently place Diretmidae as the sister lineage of all other Trachichthyiformes (Miya et al. 2003, 2005; Near et al. 2013; Betancur-R et al. 2017; Musilova et al. 2019; Ghedotti et al. 2021; Ghezelayagh et al. 2022).

  • Composition. There are currently 71 living species of Trachichthyiformes (Fricke et al. 2023) classified in Anomalopidae, Anoplogaster, Diretmidae, Monocentridae, and Trachichthyidae. Over the past 10 years, four new living species of Trachichthyiformes have been described (Su et al. 2022a, 2022b; Fricke et al. 2023), comprising 5.6% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies of Trachichthyiformes include (1) presence of X pattern on the frontal (Zehren 1979; Moore 1993b; Ghedotti et al. 2021), (2) ethmoid very small and confined to area between upper portions of lateral ethmoids (Zehren 1979; Moore 1993b; Ghedotti et al. 2021), (3) presence of bony arches over infraorbitals (Moore 1993b), (4) presence of tack-like scales on larvae (Baldwin and Johnson 1995; Konishi and Okiyama 1997), (5) presence of ornamentation on lateral face of opercle in larvae (Baldwin and Johnson 1995), and (6) presence of spicules on rays of dorsal, anal, caudal, and pectoral fins of larvae (Konishi and Okiyama 1997; Ghedotti et al. 2021).

  • Synonyms. Trachichthyoidei (Moore 1993b:115) is an ambiguous synonym of Trachichthyiformes.

  • Comments. The group name Trachichthyiformes was initially applied to the paraphyletic group that included all species of Trachichthyiformes and Beryciformes to the exclusion of Berycidae (Stiassny and Moore 1992; Moore 1993b). Trachichthyiformes was used as the group name for the clade defined here in classifications resulting from molecular phylogenetic analyses (Betancur-R et al. 2017; Ghezelayagh et al. 2022) and was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade.

  • The earliest fossil Trachichthyiformes is the trachichthyid †Gephyroberyx robustus from the Rupelian (33.9–27.82 Ma) of the Caucasus area of Russia (Danil'chenko 1960). Bayesian relaxed molecular clock analyses of Trachichthyiformes result in an average posterior crown age estimate of 46.6 million years ago, with the credible interval ranging between 24.7 and 75.5 million years ago (Ghezelayagh et al. 2022).

  • img-z106-9_03.gif

    Beryciformes A. C. L. G. Günther 1880:419
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Beryx decadactylus Cuvier in Cuvier and Valenciennes (1829b) and Holocentrus rufus (Walbaum 1792), but not Diretmus argenteus J. Y. Johnson 1864 nor Aulotrachichthys prosthemius (Jordan and Fowler 1902). This is a minimum-crown-clade definition with external specifiers.

  • Etymology. From the ancient Greek βρρυς (b̍e͡I͡ɪɹuːz) meaning fish. The word is known primarily from the lexicon of the fifth- or sixth-century CE grammarian Hesychius of Alexandria (D. W. Thompson 1947:32). The suffix is from the Latin forma meaning form, figure, or appearance.

  • Registration number. 945.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of 989 ultraconserved element loci (Ghezelayagh et al. 2022, fig. S2). Phylogenetic relationships of the major living and fossil lineages of Beryciformes are presented in Figure 14. The phylogenetic placements of the pan-holocentrids †Berybolcensis, †Iridopristis, †Plesioberyx, †Stichocentrus, and †Tenuicentrum, and the pan-berycoid †Berycomorus are on the basis of inferences from morphology (Friedman 2009; Andrews et al. 2023).

  • Phylogenetics. No phylogenetic analysis of morphological characters has resolved Beryciformes as a monophyletic group (Stiassny and Moore 1992; G. D. Johnson and Patterson 1993; Moore 1993b). Molecular phylogenetic analyses differ on the monophyly of Beryciformes, but the incongruence is limited to the identity of the sister lineage of Holocentridae (squirrelfishes). One set of molecular analyses resolves Beryciformes as paraphyletic, with Holocentridae and Percomorpha as sister lineages (Betancur-R, Broughton, et al. 2013; Smith et al. 2016; Betancur-R et al. 2017). Alternatively, another group of analyses results in phylogenies in which a monophyletic Beryciformes is placed as the sister group of Percomorpha (Figures 2 and 14; Miya et al. 2003; Thacker 2009; W.-J. Chen, Santini, et al. 2014; Malmstrøm et al. 2016; Dornburg et al. 2017; Hughes et al. 2018, fig. S2; Musilova et al. 2019; Ghezelayagh et al. 2022). Within Beryciformes, Berycoidei and Holocentridae are resolved as sister lineages (Figure 14; Miya et al. 2003, 2005; Thacker 2009; Near, Eytan, et al. 2012; W.-J. Chen, Santini, et al. 2014; Malmstrøm et al. 2016; Dornburg et al. 2017; Hughes et al. 2018, fig. S2; Musilova et al. 2019; Roth et al. 2020; Ghedotti et al. 2021; Ghezelayagh et al. 2022).

  • Composition. There are 213 living species of Beryciformes (Fricke et al. 2023) classified in Berycoidei and Holocentridae. Fossil lineages include the pan-holocentrids †Berybolcensis, †Iridopristis, †Plesioberyx, †Stichocentrus, and †Tenuicentrum (Patterson 1967; Gayet 1980a; Andrews et al. 2023), and the pan-berycoid †Berycomorus (Arambourg 1966). Details of the ages and locations of the fossil taxa are presented in Appendix 1. Over the past 10 years, 20 new living species of Beryciformes have been described (Fricke et al. 2023), comprising 9.4% of the living species diversity in the clade.

  • Diagnostic apomorphies. There are no known morphological apomorphies for Beryciformes (Moore 1993b; Ghedotti et al. 2021).

  • Synonyms. Berycimorphaceae (Betancur-R et al. 2017:21) is a partial synonym of Beryciformes.

  • Comments. Since the introduction of Beryciformes as a taxonomic group (Günther 1880), its composition has included Polymixia, Caristiidae (Scombriformes), Ostracoberyx (Acropomatiformes), and lineages now classified as Trachichthyiformes (Starks 1904; Regan 1911c; Berg 1940:467–468; Patterson 1964:432–434; McAllister 1968; Gosline 1971:147–148; Rosen 1973; J. S. Nelson 1984:232–240; G. D. Johnson and Patterson 1993; Near, Eytan, et al. 2012). A more restricted composition of Beryciformes came after the mid-20th century in a series of morphological phylogenetic studies (Zehren 1979; Stiassny and Moore 1992; Moore 1993b). Molecular phylogenetic analyses consistently support the monophyly of Beryciformes (e.g., Hughes et al. 2018, fig. S2; Ghezelayagh et al. 2022), highlighting the need for morphological studies to continue testing this hypothesis with the aim of discovering morphological apomorphies for the clade. The name Beryciformes was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade.

  • The earliest fossils of Beryciformes include the Cenomanian (100.5–93.9 Ma) pan-holocentrids †Stichocentrus liratus, †S. elegans, †S. spinulosus, †Plesioberyx maximus, and †P. discoides from Lebanon (Patterson 1967; M. Gaudant 1969; Gayet 1980a; Forey et al. 2003). Bayesian relaxed molecular clock analyses of Beryciformes result in an average posterior crown age estimate of 95.8 million years ago, with the credible interval ranging between 71.6 and 117.6 million years ago (Andrews et al. 2023).

  • img-z108-3_03.gif

    Berycoidei P. Bleeker 1874:15
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Beryx decadactylus Cuvier in Cuvier and Valenciennes (1829b) and Cetostoma regani Zugmayer 1914. This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek word βˈρυς (be͡Iɪɹuːz) meaning fish. The word is known primarily from the lexicon of the fifth- or sixth-century CE grammarian Hesychius of Alexandria (D. W. Thompson 1947:32).

  • Registration number. 946.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of 989 ultraconserved element (UCE) loci (Ghezelayagh et al. 2022, fig. S2). Phylogenetic relationships of the major lineages of Berycoidei are presented in Figure 14. The relationships of Gibberichthys follow Kobyliansky et al. (2020) and Hispidoberyx follow Moore (1993b) and Ghedotti et al. (2021).

  • Phylogenetics. No phylogenetic analysis of morphological characters has resolved Berycoidei as monophyletic (Stiassny and Moore 1992; G. D. Johnson and Patterson 1993; Moore 1993b); however, the resolution of Stephanoberycoidei in a morphological phylogeny differs from the composition of Berycoidei in the exclusion of Berycidae (alfonsinos) (Moore 1993b). With a notable exception (Colgan et al. 2000), molecular phylogenetic analyses consistently resolve Berycoidei as a clade (Miya et al. 2003, 2005; W. L. Smith and Wheeler 2006; Dettaï and Lecointre 2008; Thacker 2009; Near, Eytan, et al. 2012; T. Grande et al. 2013; Near et al. 2013; Davis et al. 2016; Betancur-R et al. 2017; Hughes et al. 2018; Rabosky et al. 2018; Ghedotti et al. 2021; Ghezelayagh et al. 2022). Within Berycoidei, Berycidae and Melamphaidae (ridgeheads) comprise a clade that is the sister lineage to all other berycoids (e.g., Miya et al. 2003; Near et al. 2013; Betancur-R et al. 2017; Ghezelayagh et al. 2022). Molecular phylogenies differ on the relationships of Barbourisia rufa (Velvet Whalefish), Cetomimidae (flabby whalefishes), and Stephanoberycidae (pricklefishes). Phylogenies inferred from mtDNA or combinations of mtDNA and nuclear genes resolve Barbourisia and Cetomimidae as sister lineages (Near et al. 2013; Rabosky et al. 2018; Kobyliansky et al. 2020; Ghedotti et al. 2021), consistent with inferences from morphology (Moore 1993b). However, phylogenetic analyses of a supermatrix of Sanger-sequenced genes and a dataset comprising more than 980 UCE loci resolve Barbourisia and Stephanoberycidae as a clade (Betancur-R et al. 2017; Ghezelayagh et al. 2022).

  • Morphological phylogenies resolve Gibberichthys (gibberfishes) as the sister lineage of a clade containing Hispidoberyx ambagiosus (Bristlyskin) and Stephanoberycidae, and resolve the deepsea whalefishes as a monophyletic group comprising Barbourisia, Cetomimidae, and Rondeletia (red mouth whalefishes) (Moore 1993b). However, the presence of Tominaga's organ, a large globular mass of tissue below the nasal rosette with a potential secretory function, was presented as morphological evidence that Gibberichthys and Rondeletia are sister lineages (Paxton et al. 2001), a result supported in a phylogenetic analysis of mtDNA gene sequences (Kobyliansky et al. 2020). The previously recognized lineages Mirapinnidae (tapetails) and Megalomycteridae (bignose fishes) are larvae and males, respectively, of species of Cetomimidae (G. D. Johnson et al. 2009).

  • Composition. There are currently 123 living species of Berycoidei that include Barbourisia rufa, Hispidoberyx ambagiosus, and species classified in Berycidae, Cetomimidae, Gibberichthys, Melamphaidae, Rondeletia, and Stephanoberycidae. Over the past 10 years, 13 new living species of Berycoidei have been described (Fricke et al. 2023), comprising 10.6% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Berycoidei are found in all lineages except Berycidae and include (1) ocular sclera absent (Moore 1993b; Ghedotti et al. 2021), (2) orbitosphenoid absent (Moore 1993b; Ghedotti et al. 2021), (3) cranium with thinly ossified bones consisting mostly of cartilage and connective tissue (Moore 1993b; Ghedotti et al. 2021), and (4) lower branchial tooth patches absent (Moore 1993b; Ghedotti et al. 2021).

  • Synonyms. Stephanoberycoidei (Moore 1993b, fig. 5; J. S. Nelson et al. 2016:308–309; Betancur-R et al. 2017:21; Afonso et al. 2021) is a partial synonym of Berycoidei.

  • Comments. The group name Berycoidei has been applied to several para- and polyphyletic groups, including: (1) Trachichthyidae and Holocentridae (Patterson 1964); (2) Berycidae, Trachichthyidae, Diretmidae, Anoplogaster, Anomalopidae, and Holocentridae (Greenwood et al. 1966); (3) Berycidae and Melamphaidae (J. S. Nelson et al. 2016:313–314; Betancur-R et al. 2017); or (4) limited to Berycidae (Nelson 1994:288, 2006:302–303). The composition of Berycoidei as defined here follows the results of several molecular phylogenetic analyses (e.g., Davis et al. 2016; Betancur-R et al. 2017; Hughes et al. 2018; Rabosky et al. 2018; Ghedotti et al. 2021; Ghezelayagh et al. 2022) and was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade.

  • Bayesian relaxed molecular clock analyses of Berycoidei result in an average posterior crown age estimate of 85.8 million years ago, with the credible interval ranging between 65.8 and 101.9 million years ago (Ghezelayagh et al. 2022).

  • img-z109-8_03.gif

    Percomorpha O. P. Hay 1903:693
    [T. J. Near and C. E. Thacker], converted clade name

  • Definition. The least inclusive crown clade that contains Carapus bermudensis (Jones 1874) (Ophidiiformes), Perca fluviatilis Linnaeus 1758 (Perciformes), and Micropterus salmoides (Lacépède 1802) (Centrarchiformes), but not Diretmoides pauciradiatus (Woods 1973) in Woods and Sonoda (1973) (Trachichthyiformes) nor Beryx decadactylus Cuvier 1829 in Cuvier and Valenciennes (1829b) (Beryciformes). This is a minimum-crown-clade definition with external specifiers.

  • Etymology. From the ancient Greek πέρκη (p̍ːke͡I), a name applied to many species of fishes by ancient authors (D. W. Thompson 1947:195–197) and µoρϕή (m̍ͻfiː) meaning form or shape.

  • Registration number. 947.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of 989 ultraconserved element loci (Ghezelayagh et al. 2022, figs. S3–S25). Phylogenetic relationships of Percomorpha are shown in Figures 2 and 14. In the phylogeny, the placement of the fossil pan-ophidiiform †Pastorius is the more conservative of two hypotheses presented by Carnevale and Johnson (2015) and resolution of the pan-batrachoid †Bacchiaichthys follows Carnevale and Collette (2014).

  • Phylogenetics. Percomorpha was first delimited as a result of comparative morphological studies and included all lineages currently classified in Acanthopterygii except Atheriniformes (=Atherinomorpha), Batrachoididae, Lophioidei (=Lophiiformes), and Ophidiiformes (Rosen and Patterson 1969). Over the next two decades, Percomorpha and Atheriniformes were presented as sister lineages in several phylogenetic trees (Hinegardner and Rosen 1972; Rosen 1973, 1982; C. L. Smith 1975; Rosen and Parenti 1981; Lauder 1983; Lauder and Liem 1983). During this period, Percomorpha was identified as a clade that was inadequately diagnosed with morphological characters and contained many lineages with unresolved relationships (Rosen 1982; Lauder and Liem 1983). Subsequent morphological phylogenetic studies indicated that Rosen and Patterson's (1969) concept of Percomorpha was paraphyletic due to the resolution of Mugilidae as the sister lineage to Atheriniformes (Stiassny 1990, 1993). A subsequent review and investigation of acanthomorph phylogeny based on 34 morphological characters led to a redefinition of Percomorpha to include Atheriniformes and exclude Trachichthyiformes and Beryciformes (G. D. Johnson and Patterson 1993).

  • Phylogenies resulting from analyses of molecular data offer a refined delimitation of Percomorpha that not only includes Atheriniformes, but also the lineages Batrachoididae, Lophioidei, and Ophidiiformes that were previously classified in Paracanthopterygii (W.-J. Chen et al. 2003; Miya et al. 2003, 2005). Subsequent molecular phylogenetic analyses consistently support the monophyly of this revised delimitation of Percomorpha (W. L. Smith and Wheeler 2006; Davis 2010; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; T. Grande et al. 2013; Near et al. 2013; W.-J. Chen, Santini, et al. 2014; Davis et al. 2016; Malmstrøm et al. 2016, 2017; Smith et al. 2016; Betancur-R et al. 2017; Alfaro et al. 2018; Hughes et al. 2018; Roth et al. 2020; Ghezelayagh et al. 2022; Mu et al. 2022; J.-F. Wang et al. 2023). Molecular studies with inclusive taxon sampling resolve 13 major clades within Percomorpha, with Ophidiiformes and Batrachoididae as the first of two successive branching lineages in the clade; Scombriformes and Syngnathiformes as sister lineages; a clade containing Ovalentaria, Synbranchiformes, and Carangiformes; and Eupercaria as a clade containing Perciformes, Centrarchiformes, Labriformes, Acropomatiformes, and Acanthuriformes (Near et al. 2013; Smith et al. 2016; Betancur-R et al. 2017; Dornburg and Near 2021; Ghezelayagh et al. 2022). Phylogenetic analyses of morphological characters support the monophyly of Percomorpha (Davesne et al. 2016; Cantalice et al. 2021), but these studies limit taxon sampling to four species, one representing each of Acanthuriformes, Batrachoididae, Carangiformes, and Ophidiiformes.

  • Composition. Percomorpha currently includes more than 18,900 living species (Fricke et al. 2023), classified in the subclades Ophidiiformes, Batrachoididae, Syngnathiformes, Scombriformes, Ovalentaria, Gobiiformes, Synbranchiformes, Carangiformes, and Eupercaria. Fossil lineages include the pan-ophidiiform †Pastorius (Carnevale and Johnson 2015) and the pan-batrachoid †Bacchiaichthys (Bannikov and Sorbini 2000; Carnevale and Collette 2014). Details of the ages and locations for the fossil taxa are given in Appendix 1. Over the past 10 years, 1,090 new living species of Percomorpha have been described (Fricke et al. 2023), comprising 5.8% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Percomorpha include (1) external dorsal pelvic wing equal in size to external ventral wing (Stiassny and Moore 1992; Davesne et al. 2016), (2) first epibranchial and second pharyngobranchial with rodlike interarcual cartilage present between separated uncinate processes (G. D. Johnson and Patterson 1993; W. L. Smith 2005; Wiley and Johnson 2010), (3) absence of second ural centrum (G. D. Johnson and Patterson 1993; Wiley and Johnson 2010), (4) five or fewer hypurals (G. D. Johnson and Patterson 1993; Wiley and Johnson 2010), (5) fewer than six rays in pelvic fin (G. D. Johnson and Patterson 1993; Wiley and Johnson 2010; Davesne et al. 2016), (6) absence of free pelvic radials (G. D. Johnson and Patterson 1993; Wiley and Johnson 2010; Davesne et al. 2016), (7) all but the first two epineurals have a point of origin that is displaced ventrally with distal parts of all epineurals displaced ventrally into the horizontal septum (G. D. Johnson and Patterson 1993; Wiley and Johnson 2010), (8) 17 principal caudal rays arranged as I,8,7,I (G. D. Johnson and Patterson 1993; Wiley and Johnson 2010; Davesne et al. 2016; Cantalice et al. 2021), (9) absence of anterior supramaxilla (Davesne et al. 2016; Cantalice et al. 2021), (10) absence of orbitosphenoid (Davesne et al. 2016; Cantalice et al. 2021), (11) anterior and posterior ceratohyals sutured (Davesne et al. 2016), and (12) the first dorsal pterygiophore inserts between neural spines 2 and 4 (Davesne et al. 2016).

  • Synonyms. Percomorphacea (Wiley and Johnson 2010:127, 151–152; Betancur-R et al. 2017:22) is an ambiguous synonym of Percomorpha.

  • Comments. Percomorpha was famously referred to the “bush at the top of the tree” in reference to the limited phylogenetic resolution among the more than 18,900 species and at least 288 taxonomic families in the clade (G. J. Nelson 1989:328). This was later restated as the “percomorph problem” in reference to the lack of morphological apomorphies diagnosing the group and the fact that Percomorpha represented the largest polytomy in the phylogeny of living vertebrates, a consequence of too many lineages and too few morphological characters to resolve relationships (G. D. Johnson and Patterson 1993; Chakrabarty 2010). Despite impressive efforts that involve careful and elegant studies of comparative morphology (G. D. Johnson and Patterson 1993; Patterson and Johnson 1995; Datovo et al. 2014; Pastana et al. 2022), the status of efforts using morphology to resolve the phylogeny of Percomorpha is summarized as “any tree can be justified by special pleading, by insisting that certain characters are uniquely derived but others are more labile or plastic” as “very few of the characters found among percomorphs and their relatives are uniquely derived” (G. D. Johnson and Patterson 1993:555). Molecular phylogenetics has not only led to a dramatic increase in the resolution of relationships within Percomorpha, but has also provided a mechanism for the development of exciting and surprising hypotheses of relationships that were undiscovered and wholly unanticipated from the study of morphology (Dornburg and Near 2021). The future of phylogenetic studies of Percomorpha likely involves a full integration of molecular phylogenetics and comparative morphology as evidenced by studies that lead to reinterpretations of morphological traits in the context of phylogenies resulting from analysis of molecular data (e.g., Chanet et al. 2013; Ghedotti et al. 2018; M. G. Girard et al. 2020).

  • Since the turn of the 21st century, Percomorpha is consistently delimited as including Ophidiiformes and Batrachoididae and excluding Beryciformes and Trachichthyiformes (Miya et al. 2003, 2005; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; T. Grande et al. 2013; Near et al. 2013; W.-J. Chen, Santini, et al. 2014; Davis et al. 2016; J. S. Nelson et al. 2016:314–315; Smith et al. 2016; Betancur-R et al. 2017; Alfaro et al. 2018; Hughes et al. 2018; Dornburg and Near 2021; Ghezelayagh et al. 2022; Mu et al. 2022; J.-F. Wang et al. 2023). The name Percomorpha was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade.

  • The earliest fossils of Percomorpha all date to the Campanian and Maastrichtian (83.6–72.1, 72.1–66.0 Ma) of the Late Cretaceous and include the pan-ophidiiform †Pastorius (Carnevale and Johnson 2015), the pan-batrachoid †Bacchiaichthys (Bannikov and Sorbini 2000), and the pan-centriscoid †Gasterorhamphosus (Sorbini 1981). Bayesian relaxed molecular clock analyses of Percomorpha result in an average posterior crown age estimate of 126.8 million years ago, with the credible interval ranging between 116.9 and 135.6 million years ago (Ghezelayagh et al. 2022).

  • img-z111-7_03.gif

    Ophidiiformes P. Bleeker 1859:xxv
    [C. E. Thacker and T. J. Near], converted clade name

  • Definition. The least inclusive crown clade that contains Ophidion barbatum Linnaeus 1758, Dinematichthys iluocoeteoides Bleeker 1855, Aphyonus gelatinosus Günther 1878a, Brotula barbata (Bloch and Schneider 1801), Carapus acus (Brünnich 1768), and Dicrolene introniger Goode and Bean 1883. This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek όφίς (̍o͡ƱfIs) meaning snake. The suffix is from the Latin forma meaning form, figure, or appearance.

  • Registration number. 948.

  • Reference phylogeny. A phylogeny inferred from sequences of 989 ultraconserved element loci (Ghezelayagh et al. 2022, fig. S3). Although Ophidion barbatum is not included in the reference phylogeny, it resolves in a clade with other species of Ophidion in a phylogenomic analysis of Sanger-sequenced mitochondrial and nuclear genes (Betancur-R et al. 2017, fig. S6; Rabosky et al. 2018). Phylogenetic relationships of the major living lineages and fossil taxa of Ophidiiformes are presented in Figure 14. Placements of the fossil taxa in the phylogeny are on the basis of inferences from morphology (Patterson and Rosen 1989; Schwarzhans 2003, 2010; Møller et al. 2016; Schwarzhans and Stringer 2020).

  • Phylogenetics. Ophidiiformes was previously classified in Paracanthopterygii on the basis of studies of morphology (e.g., Greenwood et al. 1966; Rosen and Patterson 1969; Patterson and Rosen 1989; J. S. Nelson 2006:243–248), but they are distantly related to paracanthopterygians and are resolved as the sister group of all other Percomorpha in molecular phylogenetic analyses (Miya et al. 2003, 2005; W. L. Smith and Wheeler 2006; Davis 2010; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; T. Grande et al. 2013; Near et al. 2013; W.-J. Chen, Santini, et al. 2014; Davis et al. 2016; Malmstrøm et al. 2016; Betancur-R et al. 2017; Alfaro et al. 2018; Hughes et al. 2018; Roth et al. 2020; Ghezelayagh et al. 2022; Mu et al. 2022). Despite being resolved as monophyletic in analyses of molecular data (Miya et al. 2003; Near et al. 2013; Møller et al. 2016; Betancur-R et al. 2017; Campbell, Nielsen, et al. 2017; Ghezelayagh et al. 2022), there is little evidence from morphology for the monophyly of Ophidiiformes (Rosen 1985; Patterson and Rosen 1989; Howes 1992; Nielsen et al. 1999).

  • The mode of reproduction is an important trait in classifying Ophidiiformes into the oviparous Ophidiidae (cusk eels) and viviparous Bythitoidei (Cohen and Nielsen 1978; Nielsen et al. 1999; J. S. Nelson et al. 2016). Phylogenies inferred from molecular data result in paraphyly of the traditional delimitation of Ophidiidae because of the resolution of Carapidae (pearlfishes) (Miya et al. 2003, 2005; Near et al. 2013; Betancur-R et al. 2017; Rabosky et al. 2018; Ghezelayagh et al. 2022; M. G. Girard et al. 2023), prompting the delineation of a more inclusive Ophidiidae to include species previously classified in Carapidae (Betancur-R et al. 2017). Molecular phylogenetic analyses resolve both the more inclusive Ophidiidae and Bythitoidei as monophyletic groups (Near et al. 2013; Møller et al. 2016; Betancur-R et al. 2017; Campbell, Nielsen, et al. 2017; Rabosky et al. 2018; Ghezelayagh et al. 2022).

  • Composition. There are currently 569 living species of Ophidiiformes (Nielsen et al. 1999; Fricke et al. 2023) classified in Ophidiidae and Bythitoidei. Fossil lineages of Ophidiiformes include the pan-bythitoid †“Bidenichthyscrepidatus and the pan-ophiid †Ampheristus americanus (Schwarzhans 2003, 2010; Schwarzhans and Stringer 2020). Details of the ages and locations of the fossil taxa are presented in Appendix 1. Over the past 10 years, there have been 43 new living species of Ophidiiformes described (Fricke et al. 2023), comprising 7.6% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Ophidiiformes include (1) supraoccipital excluded from posterior cranial margin by posterodorsal extension of exoccipitals (Howes 1992; Carnevale and Johnson 2015), (2) presence of angled bursa-like cavity between exoccipitals and basioccipital, and (3) posterior portion of first infraorbital covered by second infraorbital (Ohashi 2018).

  • Synonyms. Ophidiicae (Hubbs 1952:51, fig. 1), Ophidiimorpharia (Betancur-R, Broughton, et al. 2013:13), Ophidiida (J. S. Nelson et al. 2016:315), and Ophidiaria (Sanciangco et al. 2016, fig. 1; Betancur-R et al. 2017:22) are ambiguous synonyms of Ophidiiformes.

  • Comments. Ophidiiformes is a diverse clade with more than 560 species classified among 121 genera (Fricke et al. 2023), but very little of this rich diversity has been integrated into phylogenetic studies (Møller et al. 2016; Rabosky et al. 2018). The migration of Ophidiiformes, Batrachoididae, and Lophioidei from Paracanthopterygii to Percomorpha speaks to the effect of molecular data on inferring the phylogeny of ray-finned fishes and is “akin to placing a morphologically established lineage of marsupials as the sister lineage of rodents or vipers as the sister lineage of Anolis” (Dornburg and Near 2021:441).

  • The earliest fossil Ophidiiformes are the pan-bythitoid †“Bidenichthyscrepidatus and the pan-ophiid †Ampheristus americanus from the Maastrichtian (72.2–66.0 Ma) in the Cretaceous (Appendix 2; Voigt 1926; Schwarzhans 2010; Schwarzhans and Stringer 2020). Bayesian relaxed molecular clock analyses of Ophidiiformes result in an average posterior crown age estimate of 84.5 million years ago, with the credible interval ranging between 59.3 and 111.3 million years ago (Ghezelayagh et al. 2022).

  • img-z113-5_03.gif

    Bythitoidei D. M. Cohen and J. G. Nielsen 1978:42
    [C. E. Thacker and T. J. Near], converted clade name

  • Definition. The least inclusive crown clade that contains Bythites fuscus Reinhardt 1837, Dinematichthys iluocoeteoides Bleeker 1855, and Aphyonus gelatinosus Günther 1878a. This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek βῠθὀς (bˈuːθo͡Ʊz) meaning the depths of the sea.

  • Registration number. 949.

  • Reference phylogeny. A phylogeny inferred from sequences of 989 ultraconserved element loci (Ghezelayagh et al. 2022, fig. S3). Although Bythites fuscus is not included in the reference phylogeny, morphological studies indicate that B. fuscus, species of Grammonus, and species of Cataetyx share common ancestry (Cohen and Nielsen 1978). Phylogenetic relationships of the major living lineages and fossil taxa of Bythitoidei are presented in Figure 14. Placements of the fossil taxa in the phylogeny are on the basis of inferences from morphology (Schwarzhans 2003, 2010; Møller et al. 2016; Schwarzhans and Stringer 2020).

  • Phylogenetics. Bythitoidei was delimited to include Bythitidae (livebearing brotulas) and Aphyonidae (aphyonids) based on the presence of an intromittent organ in males and the placement of the anterior nostril well above the upper lip (Cohen and Nielsen 1978). From the late 1960s through the 1990s, Parabrotulidae (false brotulas) was classified in Zoarcoidei on the basis of the presence of a one-to-one ratio of vertebrae to fin pterygiophores, an eel-shaped body, ventral fins, lack of fin spines, and a confluent dorsal and anal fin (Nielsen 1968; Cohen and Nielsen 1978; Nielsen et al. 1990; Miya and Nielsen 1991). It was argued that the presence of paired nostrils, a bilobed ovary, and a well-developed intromittent organ in Parabrotulidae is evidence for their shared ancestry with Ophidiiformes, specifically Bythitoidei, and not Zoarcoidei (Anderson 1994; Nelson 1994:227). A detailed analysis of the osteology of Parabrotula plagiophthalmus highlighted the morphology of the intromittent organ and the presence of six caudal rays as consistent with shared common ancestry of Parabrotulidae and Bythitidae (Hilton et al. 2021).

  • Molecular phylogenetic analyses consistently resolve Bythitoidei as monophyletic (Near et al. 2013; Møller et al. 2016; Betancur-R et al. 2017; Campbell, Nielsen, et al. 2017; Evseenko et al. 2018; Arroyave et al. 2022; Ghezelayagh et al. 2022). Parabrotulidae and the abyssal Aphyonidae are phylogenetically nested in Bythitidae, while Bythitidae and Dinematichthyidae (viviparous brotulas) are resolved as sister lineages making up the more inclusive clade Bythitoidei (Møller et al. 2016; Betancur-R et al. 2017; Campbell, Nielsen, et al. 2017; Ghezelayagh et al. 2022). The results from molecular phylogenetic analyses were the basis for the reclassification of Aphyonidae and Parabrotulidae within Bythitidae and the elevation of Dinematichthyidae from lineages formerly classified in Dinematichthyini (Møller et al. 2016).

  • Composition. There are currently 246 living species of Bythitoidei (Møller et al. 2016; Fricke et al. 2023) classified in Bythitidae and Dinematichthyidae. Fossil lineages of Bythitoidei include †Bythitidarum rasmussenae from the Danian (66.0–61.7 Ma) of Denmark (Appendix 1; Schwarzhans 2003; Møller et al. 2016). Over the past 10 years, there have been 13 new living species of Bythitoidei described (Fricke et al. 2023), comprising 5.3% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Bythitoidei include (1) presence of a male intromittent organ (Cohen and Nielsen 1978; Patterson and Rosen 1989; Wiley and Johnson 2010), (2) anterior nostril positioned low on snout and close to upper lip (Cohen and Nielsen 1978; Patterson and Rosen 1989), and (3) reduction of pelvic fin to a single ray or entirely absent (Møller et al. 2016).

  • Synonyms. There are no synonyms of Bythitoidei.

  • Comments. The earliest fossil taxon of Bythitoidei is the otolith species †Bythitidarum rasmussenae from the Danian (66.0–61.7 Ma) of Denmark (Schwarzhans 2003; Møller et al. 2016). Bayesian relaxed molecular clock analyses of Bythitoidei result in an average posterior crown age estimate of 46.0 million years ago, with the credible interval ranging between 28.1 and 69.3 million years ago (Ghezelayagh et al. 2022).

  • img-z114-6_03.gif

    Batrachoididae D. S. Jordan 1896:231
    [C. E. Thacker and T. J. Near], converted clade name

  • Definition. The least inclusive crown clade that contains Opsanus tau (Linnaeus 1766), Batrachoides pacifici (Günther 1861), and Halobatrachus didactylus (Bloch and Schneider 1801). This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek word βάτρχoς (bætɹ̍æko͡Ʊz) meaning frog.

  • Registration number. 950.

  • Reference phylogeny. A phylogeny inferred from sequences of 989 ultraconserved element loci (Ghezelayagh et al. 2022, fig. S3). The phylogenetic resolution of Batrachoididae relative to other lineages of Percomorpha is presented in Figures 2 and 14.

  • Phylogenetics. Batrachoididae (toadfishes) was previously classified in Paracanthopterygii (e.g., Greenwood et al. 1966; Rosen and Patterson 1969; Patterson and Rosen 1989; J. S. Nelson 2006:243–248), and viewed as closely related to Lophioidei (Regan 1912c; Patterson and Rosen 1989; Datovo et al. 2014). Molecular phylogenetic analyses resolve Batrachoididae as nested within Percomorpha, and most studies place batrachoids as the sister lineage of an inclusive clade that contains all other percomorphs except for Ophidiiformes (Miya et al. 2005; W. L. Smith and Wheeler 2006; Davis 2010; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; T. Grande et al. 2013; Near et al. 2013; W.-J. Chen, Santini, et al. 2014; Davis et al. 2016; Malmstrøm et al. 2016; Betancur-R et al. 2017; Alfaro et al. 2018; Hughes et al. 2018; Roth et al. 2020; Ghezelayagh et al. 2022; Mu et al. 2022).

  • The monophyly of Batrachoididae is supported in several molecular and morphological phylogenetic analyses (W. L. Smith and Wheeler 2006; Near et al. 2013; Betancur-R et al. 2017; Hughes et al. 2018; Rabosky et al. 2018; Vaz 2020; Ghezelayagh et al. 2022). Morphological and molecular phylogenetic studies infer relationships within Batrachoididae that are congruent, with Halophryninae resolved as the sister group of a clade containing Batrachoidinae, Porichthyinae, and Thalassophryninae (Greenfield et al. 2008; Rice and Bass 2009; Rabosky et al. 2018). A detailed description of the caudal skeleton identified potential apomorphies for Batrachoididae and several subclades (Vaz and Hilton 2020). A phylogenetic analysis of 191 morphological characters with extensive taxon sampling resolves lineages of Batrachoididae in a polytomy containing Triathalassothia, a clade of lineages traditionally classified in Halophryninae (Barchatus, Batrichthys, Bifax, Chatrabus, Colletteichthys, Halobatrachus, Perulibatrachus, and Riekertia), and a clade containing Halophryninae (Allenbatrachus, Batrachomoeus, and Halophryne), Thalassophryninae (Daector and Thalassophryne), Porichthyinae (Aphos and Porichthys), and Batrachoidinae (Amphichthys, Batrachoides, Opsanus, Sanopus, and Vladichthys) (Vaz 2020).

  • Composition. There are currently 84 living species of Batrachoididae (Fricke et al. 2023) that include Bifax lacinia, Halobatrachus didactylus, Riekertia ellisi, and species classified in Batrachoidinae, Halophryninae, Porichthyinae, Thalassophryninae, and Triathalassothia (Greenfield et al. 2008; Vaz 2020; Fricke et al. 2023). Over the past 10 years, one new living species of Batrachoididae was described (Fricke et al. 2023), comprising 1.2% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Batrachoididae include (1) large yolk sac with a ventral adhesive disc present in larvae (Wiley and Johnson 2010), (2) tightly packed configuration in the dorsal spine and pterygiophore complex (Wiley and Johnson 2010), (3) robust and hypertrophied epineural bound to medial surface of cleithrum (Wiley and Johnson 2010; Vaz 2020), (4) supracleithrum articulates with ankylosed posttemporal (Wiley and Johnson 2010; Vaz 2020), (5) parietals absent (Wiley and Johnson 2010), (6) mesethmoid unossified (Wiley and Johnson 2010; Vaz 2020), (7) swimbladder heart shaped with anterior portion separated in two lobes with bands of musculature along the lateral surface of each lobe (Wiley and Johnson 2010), (8) dorsal edge of metapterygoid with a trapezoidal shape (Vaz 2020), (9) subopercle with one, two, or three spines (Vaz 2020), (10) urohyal with lateral projections giving a T-shape (Vaz 2020), (11) uncinate process longer than the anterior half of epibranchial process (Vaz 2020), (12) fifth ceratobranchial is one-half the length of fourth ceratobranchial (Vaz 2020), (13) origin of first epineural bone articulates with the neural spine of the first vertebra (Vaz 2020), (14) the origin of third epineural at the level of neural arch of third vertebra (Vaz 2020), (15) ventral limb of posttemporal reduced to a knob (Vaz 2020), (16) presence of anterodorsal process of the supracleithrum, (17) propterygium hypertrophied as long pectoral radials (Vaz 2020; Vaz and Hilton 2023), (18) propterygium rod shaped (Vaz 2020), and (19) presence of a filamentous cushion organ on the pelvic spine and lateralmost soft ray (Vaz 2020).

  • Synonyms. Haplodoci (Cope 1871a:458), Batrachoidiformes (Berg 1937:1279; Greenwood et al. 1966:396; Lauder and Liem 1983, fig. 37; Patterson and Rosen 1989:23–24; Wiley and Johnson 2010:159–160; J. S. Nelson et al. 2016:320–321; Betancur-R et al. 2017:22), Batrachoidimorpharia (Betancur-R et al. 2013a:13), Batrachoidida (J. S. Nelson et al. 2016:320), and Batrachoidaria (Betancur-R et al. 2017:22) are ambiguous synonyms of Batrachoididae.

  • Comments. Batrachoididae is a valid family-group name under the International Code of Zoological Nomenclature (Van der Laan et al. 2014:64), has long been applied as the group name for the clade presented in the definition (Jordan 1923:238; McAllister 1968:164; J. S. Nelson et al. 2016:321–323), and was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade.

  • The earliest fossil taxon of Batrachoididae is the otolith-based species †Batrachoididarum trapezoidalis from the Ypresian (56.0–48.1 Ma) of France (Nolf 1988; Carnevale and Collette 2014), and the earliest skeletal fossil is †Louckaichthys novosadi from the Rupelian (33.9–27.3 Ma) of the Czech Republic (Přikryl and Carnevale 2017). Bayesian relaxed molecular clock analyses of Batrachoididae result in an average posterior crown age estimate of 49.1 million years ago, with the credible interval ranging between 25.3 and 76.3 million years ago (Ghezelayagh et al. 2022).

  • img-z116-2_03.gif

    Gobiiformes P. Bleeker 1859:xxv
    [C. E. Thacker and T. J. Near], converted clade name

  • Definition. The least inclusive crown clade that contains Gobius niger Linnaeus 1758, Lythrypnus dalli (Gilbert 1890), Trichonotus filamentosus (Steindachner 1867), Ostorhinchus doederleini (Jordan and Snyder 1901), and Kurtus indicus Bloch 1786. This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek κωβιός (k̍o͡ƱbIo͡Ʊz) meaning small insignificant fish. The suffix is from the Latin forma meaning form, figure, or appearance.

  • Registration number. 951.

  • Reference phylogeny. A phylogeny inferred from sequences of 989 ultraconserved element loci (Ghezelayagh et al. 2022, figs. S3, S4). Although Gobius niger is not included in the reference phylogeny, it resolves in a clade with other species of Gobiidae in phylogenetic analyses of Sanger-sequenced mitochondrial and nuclear genes (Tornabene et al. 2013, fig. 2; McCraney et al. 2020, fig. 6). Phylogenetic relationships among the major lineages of Gobiiformes are presented in Figure 14. Placement of the fossil pan-gobioid †Paralates in the phylogeny is on the basis of an analysis of morphological characters (Gierl et al. 2022).

  • Phylogenetics. One of the most remarkable results from molecular phylogenetic analyses of Percomorpha is the discovery that Apogonidae, Gobioidei, Kurtus, and Trichonotus resolve in a strongly supported clade, delimited here as Gobiiformes, that is the sister lineage of a clade containing all other lineages of Percomorpha exclusive of Ophidiiformes and Batrachoididae (Thacker and Hardman 2005; W. L. Smith and Wheeler 2006; W. L. Smith and Craig 2007; Thacker 2009; Thacker and Roje 2009; Chakrabarty et al. 2012; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; Near et al. 2013; Thacker et al. 2015; Betancur-R et al. 2017; Alfaro et al. 2018; Hughes et al. 2018; Kuang et al. 2018; McCraney et al. 2020; Ghezelayagh et al. 2022; Satoh and Katayama 2022). Within Gobiiformes, a clade containing Gobioidei and Trichonotus is the sister lineage of Apogonoidei, including Apogonidae and Kurtus (Near et al. 2013; Thacker et al. 2015; Betancur-R et al. 2017; Rabosky et al. 2018; McCraney et al. 2020; Ghezelayagh et al. 2022). Alternative phylogenetic relationships among Gobiiformes resulting from molecular phylogenetic analyses include the resolution of Kurtus as the sister lineage of all other Gobiiformes (Thacker 2009; Chakrabarty et al. 2012; Alfaro et al. 2018; Kuang et al. 2018) and a clade containing Apogonidae, Kurtus, and Trichonotus as the sister lineage of Gobioidei (Satoh and Katayama 2022).

  • Composition. There are currently 2,740 living species of Gobiiformes (Fricke et al. 2023) classified in Apogonoidei, Gobioidei, and Trichonotus. Fossil lineages include the pan-gobioid †Paralates (Gierl and Reichenbacher 2017; Gierl et al. 2022). Over the past 10 years, 368 new living species of Gobiiformes have been described (Fricke et al. 2023), comprising 13.4% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Gobiiformes include (1) presence of large gap between symplectic and preopercle in Gobioidei and Trichonotus (J. S. Nelson 1986; Winterbottom 1993b), (2) presence of sensory papillae rows on the head and body in Gobioidei, Kurtus, and Apogonidae (G. D. Johnson 1993; Thacker 2009), but see Sato (2022), and (3) presence of eggs with adhesive filaments around the micropyle in Gobioidei, Kurtus, and Apogonidae (G. D. Johnson 1993; Thacker et al. 2015). All Gobiiformes engage in egg guarding or brooding by the male, either in a benthic nest (Gobioidei), in the mouth (Apogonidae), on the forehead (Kurtus), or in the gill chamber (Trichonotus) (Clark and Pohle 1996; Berra and Humphrey 2002; Östlund-Nilsson and Nilsson 2004; Thacker et al. 2015).

  • Synonyms. Gobiomorpharia (Betancur-R, Broughton, et al. 2013, fig. 1) and Gobiaria (Betancur-R et al. 2017:23) are ambiguous synonyms of Gobiiformes. Gobiida (J. S. Nelson et al. 2016:323) is a partial synonym of Gobiiformes.

  • Comments. Gobiiformes has been applied as a group name for (1) a group that included Apogonidae, Gobioidei, Kurtus, and Pempheridae (Thacker 2009); (2) a clade containing Trichonotus and Gobioidei (Betancur-R et al. 2017); and (3) a clade containing Apogonoidei, Gobioidei, and Trichonotus as presented here in the definition (Thacker et al. 2015; Davis et al. 2016; Dornburg and Near 2021; Ghezelayagh et al. 2022). The name Gobiiformes was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade.

  • The resolution of a monophyletic Gobiiformes is one of many unexpected results stemming from molecular phylogenetic analyses of Percomorpha. Morphological studies exploring the phylogenetic affinities of Apogonidae, Gobioidei, Kurtus, and Trichonotus all predate the resolution of these lineages as a clade in molecular studies (G. D. Johnson 1993; Winterbottom 1993b; D. G. Smith and Johnson 2007). A potentially fruitful area of future research is the exploration of comparative morphological and anatomical studies among the seemingly disparate lineages that comprise Gobiiformes, with the goal of understanding their history of phenotypic trait diversification and the discovery of additional morphological apomorphies.

  • The earliest fossils of Gobiiformes are the otolith-based species of †Apogonidarum classified as Apogonidae from the Maastrichtian (72.2–66.0 Ma) in the Cretaceous of India and North Dakota, USA (Khajuria and Prasad 1998; Hoganson et al. 2019). The earliest skeletal fossils of Gobiiformes include the gobioid †Carlomonnius and the apogonids †Apogoniscus, †Bolcapogon, †Eoapogon, †Eosphaeramia, and †Leptolumamia all from the Ypresian (56.0–48.1 Ma) of Monte Bolca, Italy (Bannikov and Carnevale 2016; Bannikov and Fraser 2016). Bayesian relaxed molecular clock analyses of Gobiiformes result in an average posterior crown age estimate of 109.6 million years ago, with the credible interval ranging between 98.9 and 119.9 million years ago (Ghezelayagh et al. 2022).

  • img-z117-7_03.gif

    Gobioidei Bleeker 1849:4
    [C. E. Thacker and T. J. Near], converted clade name

  • Definition. The least inclusive crown clade that contains Gobius niger Linnaeus 1758, Lythrypnus dalli (Gilbert 1890), Periophthalmus barbarus (Linnaeus 1766), Eleotris pisonis (Gmelin 1789), Milyeringa veritas Whitley 1945, and Rhyacichthys aspro (Valenciennes in Cuvier and Valenciennes 1837). This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek κωβιός (k̍o͡ƱbIˌo͡Ʊz) meaning small insignificant fish.

  • Registration number. 952.

  • Reference phylogeny. A phylogeny inferred from sequences of 989 ultraconserved element (UCE) loci (Ghezelayagh et al. 2022, fig. S4). Although Gobius niger is not included in the reference phylogeny, it resolves in a clade with other species of Gobiidae in phylogenetic analyses of Sanger-sequenced mitochondrial and nuclear genes (Tornabene et al. 2013, fig. 2; McCraney et al. 2020, fig. 6). Phylogenetic relationships among the living and fossil lineages of Gobioidei are presented in Figure 14. Placements of the fossil pan-butids †Carlomonnius and †Lepidocottus and the pan-thalasseleotrids †Eleogobius and †Pirskenius follow Gierl et al. (2022).

  • Phylogenetics. Prior to the application of molecular data to the study of fish phylogeny, the relationships of Gobioidei among Percomorpha were unresolved (P. J. Miller 1973, 1986; Springer 1983; Hoese 1984). In a study of osteological characters, Winterbottom (1993b) concluded that Hoplichthys, Gobiesocidae, Callionymidae, and various “trachinoids” that included Creediidae, Hemerocoetidae, and Trichonotus were the lineages with the greatest number of character states shared with Gobioidei. Despite many morphological apomorphies diagnosing Gobioidei (Springer 1983; Hoese 1984; P. J. Miller 1992; G. D. Johnson and Brothers 1993; Winterbottom 1993b), comparative morphological studies did not provide a strong hypothesis for the phylogenetic affinities of gobioids among percomorphs. Morphology of the dorsal gill arches was cited as evidence of shared common ancestry for Apogonidae and Kurtus (G. D. Johnson 1993).

  • Gobioidei is consistently resolved as monophyletic in molecular phylogenetic studies (W. L. Smith and Wheeler 2006; Thacker 2009; Near, Eytan, et al. 2012; Betancur-R, Broughton, et al. 2013; Near et al. 2013; Thacker et al. 2015, 2023; Betancur-R et al. 2017; Hughes et al. 2018; Kuang et al. 2018; McCraney et al. 2020; Ghezelayagh et al. 2022). Within Gobioidei, molecular phylogenies resolve a clade containing Rhyacichthyidae (loach gobies) and Odontobutidae (freshwater sleepers) as the sister lineage of all other gobioids, with Milyeringidae (blind cave gobies), Eleotridae (spinycheek sleepers), Butidae (butid sleepers), and Thalasseleotrididae (ocean sleepers) as successive branching lineages leading to a clade containing Gobiidae (gobies) and Oxudercidae (mudskippers and relatives) (Thacker et al. 2015; McCraney et al. 2020; Ghezelayagh et al. 2022; Goatley and Tornabene 2022). A phylogenomic analysis of Gobioidei using UCE loci resolves Xenisthmus and Butidae as sister lineages, prompting the elevation of Xenisthmidae (collared wrigglers) out of synonymy with Eleotridae (Thacker 2003; McCraney 2019).

  • Phylogenies inferred from morphological characters are fairly congruent with relationships inferred from molecular data (Hoese and Gill 1993), specifically in resolving Rhyacichthyidae and Odontobutidae as the sister lineage of all other gobioids and supporting Thalasseleotrididae as the sister lineage of a clade containing Gobiidae and Oxudercidae (A. C. Gill and Mooi 2012; Reichenbacher et al. 2020; Gierl et al. 2022). The presence of five branchiostegal rays is consistent with the monophyly of a clade containing the gobioid lineages Thalasseleotrididae, Oxudercidae, and Gobiidae (Hoese 1984; Hoese and Gill 1993; A. C. Gill and Mooi 2012; Reichenbacher et al. 2020); the remaining lineages Rhyacichthyidae, Odontobutidae, Milyeringidae, Xenisthmidae, Eleotridae, and Butidae all have six branchiostegal rays. Molecular phylogenetic studies focusing on specific gobioid lineages have attempted to resolve relationships within Rhyacichthys (Haÿ et al. 2022), Odontobutidae (H. Li et al. 2018), Butidae, and Eleotridae (Thacker and Hardman 2005; Thacker 2017; Thacker, Shelley, McCraney, Adams, et al. 2022; Thacker, Shelley, McCraney, Unmack, et al. 2022), Oxudercidae (Yamada et al. 2009; Thacker 2013; Thacker et al. 2019; McMahan et al. 2021), and Gobiidae (Rüber et al. 2003; Herler et al. 2009; Neilson and Stepien 2009; Thacker and Roje 2011; Tornabene et al. 2013, 2023).

  • Composition. There are currently 2,347 living species of Gobioidei (Fricke et al. 2023) classified in Rhyacichthyidae, Odontobutidae, Milyeringidae, Xenisthmidae, Butidae, Eleotridae, Thalasseleotrididae, Oxudercidae, and Gobiidae. Fossil Gobioidei include the pan-butids †Carlomonnius and †Lepidocottus and the pan-thalasseleotrids †Eleogobius and †Pirskenius (Gierl et al. 2013, 2022; Přikryl 2014; Gierl and Reichenbacher 2015; Bannikov and Carnevale 2016; Reichenbacher et al. 2020). Details of the ages and locations of the fossil taxa are presented in Appendix 1. Over the past 10 years, 349 new living species of Gobioidei have been described (Fricke et al. 2023), comprising 14.9% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Gobioidei include (1) parietals absent (Springer 1983; G. D. Johnson and Brothers 1993; Winterbottom 1993b), (2) basisphenoid absent (Springer 1983; G. D. Johnson and Brothers 1993; Winterbottom 1993b), (3) two or fewer (usually zero) infraorbitals (Springer 1983; G. D. Johnson and Brothers 1993), (4) interhyal attached to preopercle by a ligament, not articulating at junction of symplectic and hyomandibular, resulting in gap between symplectic and preopercle (Springer 1983; G. D. Johnson and Brothers 1993; Winterbottom 1993b), (5) basibranchial 1 cartilaginous (Springer 1983; Winterbottom 1993b), (6) pelvic intercleithral cartilage present (Springer 1983; Winterbottom 1993b), (7) ventral intercleithral cartilage present (Springer 1983; Winterbottom 1993b), (8) sagittae and lapilli with elongate primordia (Brothers 1984; G. D. Johnson and Brothers 1993; Winterbottom 1993b), (9) accessory sperm-duct glands present in males (P. J. Miller 1992; G. D. Johnson and Brothers 1993), (10) supraneurals absent (Springer 1983; G. D. Johnson and Brothers 1993), (11) neural and haemal arches and spines developing as membrane bones with little to no cartilaginous precursors (G. D. Johnson and Brothers 1993), (12) first neural arch fused to first centrum at earliest appearance in ontogeny (G. D. Johnson and Brothers 1993), (13) dorsalmost pectoral ray articulating with posterior margin of dorsalmost actinost or radial cartilage rather than with scapula, medial part of ray lacking enlarged articular base and in early ontogeny not embracing ovoid cartilage lying at posterodorsal corner of scapulocoracoid cartilage (G. D. Johnson and Brothers 1993), and (14) hypurals 1+2 and 3+4 fused to one another and to the urostyle (G. D. Johnson and Brothers 1993; Winterbottom 1993b).

  • Synonyms. Gobiiformes (Betancur-R, Broughton, et al. 2013, fig. 3; J. S. Nelson et al. 2016:326) is an ambiguous synonym of Gobioidei.

  • Comments. Gobioidei has long been applied as the group name for the clade presented in the definition and was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade (McAllister 1968:146–147; P. J. Miller 1973; Nelson 1994:412–418; Thacker 2009; McCraney et al. 2020).

  • Time-calibrated phylogenies of acanthopterygians have repeatedly identified Gobioidei as containing clades with significantly elevated rates of lineage diversification (Near et al. 2013; Rabosky et al. 2013, 2018; Ghezelayagh et al. 2022). Comparative studies have deployed phylogenies of Gobioidei to investigate the history of phenotypic diversification (Thacker 2014, 2017; Thacker and Gkenas 2019; Huie et al. 2020) and the biogeography of near-shore marine habitats (Thacker 2015, 2017; Tornabene et al. 2016).

  • The earliest Gobioidei fossil is the pan-butid †Carlomonnius from the Ypresian (56.0–47.8 Ma) of Monte Bolca, Italy (Bannikov and Carnevale 2016). Bayesian relaxed molecular clock analyses of Gobioidei result in an average posterior crown age estimate of 93.6 million years ago, with the credible interval ranging between 82.1 and 104.6 million years ago (Ghezelayagh et al. 2022).

  • img-z119-7_03.gif

    Apogonoidei C. E. Thacker 2009:100
    [C. E. Thacker and T. J. Near], converted clade name.

  • Definition. The least inclusive crown clade that contains Kurtus indicus Bloch 1786, Pseudamia gelatinosa J. B. L. Smith 1955a, Apogon imberbis (Linnaeus 1758), and Cheilodipterus quinquelineatus Cuvier 1828 in Cuvier and Valenciennes (1828). This is a minimum-crown-clade definition.

  • Etymology. From the Greek prefix α- (a-) meaning without, and the ancient Greek πώγων (p̍o͡Ʊαːn) meaning beard.

  • Registration number. 953.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of 989 ultraconserved element loci (Ghezelayagh et al. 2022, fig. S3). AlthoughApogonimberbisisnotincludedinthe reference phylogeny, it resolves in a clade with other species of Apogonidae in phylogenetic analyses of Sanger-sequenced mitochondrial and nuclear genes (Mabuchi et al. 2014, figs. 2–6). The phylogenetic relationships of Apogonoidei are presented in Figure 14.

  • Phylogenetics. The monophyly of Apogonoidei is supported in molecular phylogenetic analyses (W. L. Smith and Craig 2007; Near et al. 2013; Thacker et al. 2015; Betancur-R et al. 2017; Rabosky et al. 2018; McCraney et al. 2020; Ghezelayagh et al. 2022) and is consistent with suggestions of a close relationship between Apogonidae (cardinalfishes) and Kurtus (nurseryfishes) based on morphological characters of the gill arches, axial skeleton, and fine structures of the egg micropyle and filaments (G. D. Johnson 1993; Prokofiev 2006b).

  • Composition. There are currently 383 living species of Apogonoidei (Fricke et al. 2023) classified in Apogonidae and Kurtus. Over the past 10 years, 19 new living species of Apogonoidei have been described (Fricke et al. 2023), comprising 5.0% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Apogonoidei include (1) second epibranchial articulates with third rather than second pharyngobranchial (G. D. Johnson 1993), (2) head of third pharyngobranchial expanded and much larger than fourth (G. D. Johnson 1993), (3) fourth pharyngobranchial cartilage absent (G. D. Johnson 1993), and (4) radial ridges of simple or bifid filaments around the micropyle of the eggs (G. D. Johnson 1993).

  • Synonyms. Kurtiformes (Betancur-R, Broughton, et al. 2013, fig. 3; J. S. Nelson et al. 2016:324; Betancur-R et al. 2017:23) is an ambiguous synonym of Apogonoidei.

  • Comments. The group name Apogonoidei has been applied to (1) a group containing Apogonidae and Pempheridae (Thacker 2009; Thacker and Roje 2009), (2) limited to Apogonidae (Betancur-R, Broughton, et al. 2013; Betancur-R et al. 2017; McCraney et al. 2020), and (3) a clade containing Apogonidae and Kurtus as presented here in the definition (Thacker et al. 2015; Ghezelayagh et al. 2022). The name Apogonoidei was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade.

  • Apogonidae and Kurtus each have highly derived egg brooding behaviors in which the eggs bear filaments that allow them to adhere into a ball that is guarded in the mouth of male Apogonidae or on a forehead hook extending from the supraoccipital in Kurtus (Berra and Humphrey 2002; Berra 2003; Östlund-Nilsson and Nilsson 2004; Mabuchi et al. 2014). Several lineages of Apogonidae, including Jaydia, Rhabdamia, Siphamia, and Taeniamia, contain species with bioluminescent organs elaborated from the gut, which may host symbiotic luminescent bacteria or generate light endogenously; this luminescence has evolved multiple times within Apogonidae (Thacker 2009; Fraser 2013).

  • The earliest fossils of Apogonoidei are the otolith-based species of †Apogonidarum that are listed as Apogonidae from the Maastrichtian (72.2–66.0 Ma) in the Cretaceous of India and North Dakota, USA (Khajuria and Prasad 1998; Hoganson et al. 2019). The earliest skeletal fossils of Apogonoidei include the apogonids †Apogoniscus, †Bolcapogon, †Eoapogon, †Eosphaeramia, and †Leptolumamia, all from the Ypresian (56.0–48.1 Ma) of Monte Bolca, Italy (Bannikov and Fraser 2016). Bayesian relaxed molecular clock analyses of Apogonoidei result in an average posterior crown age estimate of 81.9 million years ago, with the credible interval ranging between 46.6 and 110.4 million years ago (Ghezelayagh et al. 2022).

  • img-z120-10_03.gif

    Scombriformes A. S. Woodward 1901:418
    [C. E. Thacker and T. J. Near], converted clade name

  • Definition. The least inclusive crown clade that contains Arripis trutta (Bloch and Schneider 1801), Icosteus aenigmaticus Lockington 1880, Scomber scombrus Linnaeus 1758, Brama japonica Hilgendorf 1878, and Trichiurus lepturus Linnaeus 1758. This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek σκόµβρoς (sk̍αːmbɹo͡Ʊz), which was the name for the Atlantic Mackerel, Scomber scombrus (D. W. Thompson 1947:243). The suffix is from the Latin forma meaning form, figure, or appearance.

  • Registration number. 954.

  • Reference phylogeny. A phylogeny inferred from sequences of 989 ultraconserved element loci (Ghezelayagh et al. 2022, figs. S5, S6). See Figures 2 and 14 for the phylogenetic resolution of Scombriformes within Percomorpha and Figure 15 for a phylogeny of the living lineages and fossil taxa comprising Scombriformes. The placements of the fossil pan-trichiurid †Anenchelum, the pan trichiuroid †Argestichthys, the pan-chiasmodontid †Bannikovichthys, the pan-pomatomid †Carangopsis, and the pan-stromateid †Pinichthys are on the basis of inferences from morphology (Bannikov 1987, 1988, 2014b; Prokofiev 2002b; Carnevale 2007; Carnevale et al. 2014; Beckett et al. 2018b; Friedman et al. 2019; Collar et al. 2022).

  • Phylogenetics. Molecular phylogenetic analyses led to the discovery of the clade delimited here as Scombriformes (W.-J. Chen et al. 2003; W. L. Smith and Craig 2007; Dettaï and Lecointre 2008; B. Li et al. 2009; Yagishita et al. 2009; Wainwright et al. 2012; Betancur-R, Broughton, et al. 2013; Miya et al. 2013; Near et al. 2013; Davis et al. 2016; Sanciangco et al. 2016; Smith et al. 2016; Betancur-R et al. 2017; Alfaro et al. 2018; Campbell et al. 2018; Hughes et al. 2018; Friedman et al. 2019; Arcila et al. 2021; Harrington et al. 2021; Ghezelayagh et al. 2022), consisting of lineages that were never grouped together in classifications based on morphology (Greenwood et al. 1966; Wiley and Johnson 2010). Scombriformes includes lineages previously classified in Scombroidei (Scombridae [mackerels and tunas], Scombrolabrax heterolepis [Longfin Escolar], Gempylidae [snake mackerels], and Trichiuridae [cutlassfishes]) and Stromateoidei (Amarsipus carlsbergi [Amparsipas], Ariomma [ariommatids], Centrolophidae [medusafishes], Nomeidae [driftfishes], Stromateidae [butterfishes], and Tetragonuridae [squaretails]) (Greenwood et al. 1966; Haedrich 1967; Collette, Potthoff, et al. 1984; Horn 1984; G. D. Johnson 1986). The billfishes, Istiophoridae (marlins) and Xiphias gladius (Swordfish), have been classified in Scombroidei since the earliest 20th century (Regan 1909b), but are distantly related to Scombriformes in molecular phylogenies (e.g., Orrell et al. 2006; Little et al. 2010; Hughes et al. 2018; Ghezelayagh et al. 2022).

  • Relationships among major lineages of Scombriformes resulting from phylogenomic analyses are characterized by a lack of resolution among the earliest nodes in the phylogeny that is likely the result of gene tree discordance and short branch lengths (e.g., Friedman et al. 2019; Arcila et al. 2021; Harrington et al. 2021; Ghezelayagh et al. 2022). Despite the limited resolution, phylogenomic analyses resolve several clades in Scombriformes that include: a clade containing Stromateidae (butterfishes), Ariomma, and Nomeidae (driftfishes); a lineage that includes Amarsipus carlsbergi (Amarsipa) as the sister lineage of a clade containing Tetragonurus (squaretails) and Chiasmodontidae (swallowers); a clade that includes Scombrolabrax heterolepis (Longfin Escolar), Lepidocybium flavobrunneum (Escolar), a paraphyletic Gempylidae (snake mackerels), and Trichiuridae (cutlassfishes); and a lineage containing Caristiidae (manefishes) and Bramidae (pomfrets) (Friedman et al. 2019; Arcila et al. 2021; Harrington et al. 2021; Ghezelayagh et al. 2022). The relationships of Scombridae (mackerels and tunas), Icosteus aenigmaticus (Ragfish), Pomatomus saltatrix (Bluefish), and Arripis (Australian Salmon) are not well resolved within Scombriformes; however, molecular analyses consistently resolve the lineages traditionally classified in Stromateoidei (e.g., Haedrich 1967; Horn 1984) as paraphyletic (Friedman et al. 2019; Arcila et al. 2021; Harrington et al. 2021; Ghezelayagh et al. 2022).

  • The monophyly of Scombriformes is not supported in a morphological analysis of 207 characters that resolves the lineages traditionally classified in Stromateoidei as a monophyletic group (Pastana et al. 2022). The paraphyly of Stromateoidei consistently resolved in molecular phylogenetic analyses (e.g., Betancur-R, Broughton, et al. 2013; Near et al. 2013; Arcila et al. 2021; Harrington et al. 2021; Ghezelayagh et al. 2022) is dismissed on the basis of the subjective assessment that morphological characters supporting stromateoid monophyly are “unparalleled and highly complex anatomical features unlikely to have evolved multiple times independently” (Pastana et al. 2022:957). There is a degree of uncertainty in the phylogenetic relationships among the major lineages of Scombriformes inferred from molecular data, including phylogenomic datasets (Arcila et al. 2021; Harrington et al. 2021); however, there is no analysis of character evolution for the traits offered as evidence for stromateoid monophyly that accommodates different models of trait evolution and uncertainty in the phylogenetic relationships of scombriforms and stromateoids.

  • Other morphological phylogenetic analyses have focused on lineages within Scombriformes that included the previous delimitations of Scombroidei and Stromateoidei (Collette, Potthoff, et al. 1984; Horn 1984; G. D. Johnson 1986; Doiuchi et al. 2004), Gempylidae and Trichiuridae (Gago 1997, 1998; Beckett et al. 2018b), and Chiasmodontidae (Melo 2009). A phylogenetic analysis of 29 morphological characters focused on Scombroidei resolves Lepidocybium flavobrunneum, long classified in Gempylidae, as the sister lineage of a clade containing all other Gempylidae and Trichiuridae (G. D. Johnson 1986), a result that is congruent with several molecular phylogenetic analyses (Friedman et al. 2019; Arcila et al. 2021; Harrington et al. 2021; Ghezelayagh et al. 2022). Phylogenetic analyses of DNA sequences from 13 mtDNA protein coding regions seems to resolve Gempylidae as monophyletic (Mthethwa et al. 2023a, 2023b), but this result is likely an artifact of limiting the outgroups to two species of Trichiuridae. There is no available family-group name to classify Lepidocybium flavobrunneum.

  • Composition. There are currently 287 living species of Scombriformes (Collette and Nauen 1983; Fricke et al. 2023) that include Amarsipus carlsbergi, Icosteus aenigmaticus, Lepidocybium flavobrunneum, Pomatomus saltatrix, Scombrolabrax heterolepis, and species classified in Ariomma, Arripis, Bramidae, Caristiidae, Centrolophidae, Chiasmodontidae, Gempylidae, Nomeidae, Scombridae, Stromateidae, Tetragonurus, and Trichiuridae. Fossil lineages of Scombriformes include the pan-stromateid †Pinichthys pulcher (Bannikov 1988), the pan-chiasmodontid †Bannikovichthys paelignus (Carnevale 2007), the pan-pomatomid †Carangopsis maximus (Agassiz 1835:42), the pan-trichiuroid †Argestichthys vysotzkyi (Prokofiev 2002b), and the pan-trichiurid †Anenchelum eocaenicum (Danilit'chenko 1962; Monsch and Bannikov 2011). Details of the ages and locations of the fossil taxa are presented in Appendix 1. Over the past 10 years, six new living species of Scombriformes have been described, comprising 2.1% of the living species diversity in the clade (Fricke et al. 2023).

  • Diagnostic apomorphies. There are no known morphologicalapomorphiesforScombriformes.

  • Synonyms. Stromateoidei (B. Li et al. 2009, tbl. 4), Pelagia (Miya et al. 2013:2; Campbell et al. 2018:172), and Pelagiaria (Betancur-R et al. 2017:22; Campbell et al. 2018:173; Friedman et al. 2019:1) are ambiguous synonyms of Scombriformes.

  • Comments. The name Scombriformes was applied to (1) the paraphyletic group containing Carangidae, Scombridae, Stromateidae, and Xiphias (Woodward 1901:418), (2) expanded to include Trichiuridae, Coryphaena, and Luvarus (Goodrich 1909:462–468), (3) limited to Scombridae (Regan 1909b), and (4) the monophyletic group as presented here in the definition (Betancur-R, Broughton, et al. 2013; Davis et al. 2016; Betancur-R et al. 2017; Dornburg and Near 2021; Ghezelayagh et al. 2022).

  • The earliest fossil Scombriformes is the scombrid †Landanichthys from the Danian (66.0–61.7 Ma) of Angola (Friedman et al. 2019). Bayesian relaxed molecular clock analyses of Scombriformes result in an average posterior crown age estimate of 72.8 million years ago, with the credible interval ranging between 66.4 and 81.7 million years ago (Friedman et al. 2019).

  • img-z123-9_03.gif

    FIGURE 15.

    Phylogenetic relationships of the major living lineages and fossil taxa of Scombriformes and Syngnathiformes. Filled circles identify the common ancestor of clades with formal names defined in the clade accounts. Open circles highlight clades with informal group names. Fossil lineages are indicated with a dagger (†). Details of the fossil taxa are presented in Appendix 1.

    img-z122-1_03.jpg

    Syngnathiformes P. Bleeker 1859:xv
    [C. E. Thacker and T. J. Near], converted clade name

  • Definition. The least inclusive crown clade that contains Pegasus volitans Linnaeus 1758, Mullus auratus Jordan and Gilbert 1882b, Callionymus curvicornis Valenciennes 1837 in Cuvier and Valenciennes (1837), Centriscus scutatus Linnaeus 1758, and Syngnathus acus Linnaeus 1758. This is a minimum-crown-clade definition.

  • Etymology. From the ancient Greek σύµφῠσις (s̍Imfuːsiz) meaning grown together or fused, especially in reference to bones, and γνάθoς (n̍æθo͡Ʊz) meaning jaw. The suffix is from the Latin forma meaning form, figure, or appearance.

  • Registration number. 955.

  • Reference phylogeny. A phylogeny inferred from sequences of 989 ultraconserved element loci (Ghezelayagh et al. 2022, figs. S7–S9). See Figures 2 and 14 for the phylogenetic resolution of Syngnathiformes within Percomorpha and Figure 15 for a phylogeny of the living lineages and fossil taxa comprising Syngnathiformes. The phylogenetic placement of the fossil pan-pegasid †Rhamphosus follows Pietsch (1978), Bannikov (2014b), Carnevale et al. (2014), and Calzoni et al. (2023); the pan-aulostomoid †Eekaulostomus follows Cantalice and Alvarado-Ortega (2016); the pan-aulostomids †Eoaulostomus, †Jurgensenichthys, †Macroaulostomus, and †Synhypuralis follows Blot (1980) and Orr (1995); the pan-fistularid †Urosphen follows Orr (1995); the pan centriscoid †Gasterorhamphosus follows Orr (1995) and Friedman (2009); the pan-centriscids †Paraeoliscus and †Paramphisile follows Blot (1980), Friedman (2009), and Brownstein (2023); the pan-solenostomids †Calamostoma and †Solenorhynchus follows Bannikov and Carnevale (2017) and Brownstein (2023); the pan-syngnathid †Prosolenostomus follows Orr (1995), A. B. Wilson and Orr (2011), and Brownstein (2023); the pan-callionymid †Gilmourella follows Carnevale and Bannikov (2019); and the pan-dactylopterid †Pterygocephalus follows Bannikov (2014b) and Carnevale et al. (2014). The phylogenetic placements of †Eekaulostomus and †Prosolenostomus differ from those presented in other phylogenetic analyses (Murray 2022).

  • Phylogenetics. Reflecting earlier classifications (e.g., Goodrich 1909:410–416), Greenwood et al. (1966) placed many lineages of Syngnathiformes, including pipefishes and seahorses, in Gasterosteiformes along with sticklebacks (e.g., Gasterosteidae) and Indostomus (armored sticklebacks). This delimitation of Gasterosteiformes was corroborated with several putative morphological synapomorphies (Pietsch 1978; G. D. Johnson and Patterson 1993; Orr 1995; Britz and Johnson 2002; Wiley and Johnson 2010).

  • The first set of molecular phylogenetic analyses aimed at relationships with Percomorpha resolved lineages traditionally classified in Gasterosteiformes into three disparately related clades (W.-J. Chen et al. 2003; Miya et al. 2003; W. L. Smith and Wheeler 2004, 2006; Dettaï and Lecointre 2005; W. L. Smith and Craig 2007; Kawahara et al. 2008; B. Li et al. 2009). Subsequent molecular phylogenetic studies with a broad taxon sampling of percomorph lineages consistently resolved Syngnathiformes as a clade containing a paraphyletic Syngnathoidei (e.g., Pegasidae, Syngnathidae, and Centriscidae), Callionymidae (dragonets), Draconettidae (slope dragonets), Mullidae (goatfishes), and Dactylopteridae (flying gurnards) (Betancur-R, Broughton, et al. 2013; Near et al. 2013; Song et al. 2014; Betancur-R et al. 2017; Alfaro et al. 2018; Hughes et al. 2018; Roth et al. 2020; Ghezelayagh et al. 2022). Molecular phylogenetic analyses of Syngnathiformes consistently resolve two lineages: a clade of benthic lineages that contains Pegasidae (seamoths), Dactylopteridae, Draconettidae, Callionymidae, and Mullidae, and a clade of the longsnouted lineages Syngnathidae (seahorses and pipefishes), Solenostomus (ghost pipefishes), Centriscidae (shrimpfishes), Macrorhamphosus (snipefishes), Aulostomus (trumpetfishes), and Fistularia (cornetfishes) (Longo et al. 2017; Santaquiteria et al. 2021; Ghezelayagh et al. 2022). Several molecular phylogenetic studies have focused on resolving relationships within Syngnathidae (Hamilton et al. 2017; Longo et al. 2017; Santaquiteria et al. 2021; Stiller et al. 2022).

  • Composition. There are currently 690 living species of Syngnathiformes (Fricke et al. 2023) classified in Aulostomus, Callionymidae, Centriscidae, Dactylopteridae, Draconettidae, Fistularia, Macroramphosidae, Mullidae, Pegasidae, Solenostomus, and Syngnathidae. Fossil lineages of Syngnathiformes include the pan-pegasid †Rhamphosus rastrum (Volta 1796); the pan-aulostomoid †Eekaulostomus cuevasae (Cantalice and Alvarado-Ortega 2016); the pan-aulostomids †Eoaulostomus bolcensis, †Jurgensenichthys elongatus, †Macroaulostomus veronensis, and †Synhypuralis banister (Blot 1980); the pan-fistularid †Urosphen dubius (Blainville 1818); the pan-centriscid †Gasterorhamphosus zuppichinii (Sorbini 1981); the pan-centriscids †Paraeoliscus robinetae and †Paramphisile weileri (Blot 1980); the pan-solenostomids †Calamostoma breviculum and †Solenorhynchus elegans (Blainville 1818; Heckel 1853); the pan-syngnathid †Prosolenostomus lessinii (Blot 1980); the pan-callionymid †Gilmourella minuta (Carnevale and Bannikov 2019); and the pan-dactylopterid †Pterygocephalus paradoxus (Agassiz 1835). Details of the ages and locations of the fossil taxa are presented in Appendix 1. Over the past 10 years, 51 new living species of Syngnathiformes have been described, comprising 7.4% of the living species diversity in the clade (Fricke et al. 2023).

  • Diagnostic apomorphies. There are no known morphological apomorphies for Syngnathiformes.

  • Synonyms. Syngnatharia (Betancur-R et al. 2017:22) is an ambiguous synonym of Syngnathiformes. Gasterosteiformes (Goodrich 1909:410–416; Greenwood et al. 1966:398; G. D. Johnson and Patterson 1993:580; J. S. Nelson 2006:308–316; Wiley and Johnson 2010:154) and Gobiesociformes (Wiley and Johnson 2010:162–163) are partial synonyms of Syngnathiformes.

  • Comments. Syngnathiformes was the name applied to the clade containing Aulostomus, Centriscidae, Fistularia, Macroramphosidae, Solenostomus, and Syngnathidae (McAllister 1968:111–114; J. S. Nelson 1984:249–253). In recent classifications of percomorphs, the name Syngnathiformes was applied for a more inclusive clade presented here in the definition (Davis et al. 2016; Betancur-R et al. 2017; Dornburg and Near 2021; Ghezelayagh et al. 2022). The name Syngnathiformes was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade.

  • The earliest fossil Syngnathiformes is the pan-centriscoid †Gasterorhamphosus zuppichinii from the Campanian and Maastrichtian (83.6–66.0 Ma) of Italy. Bayesian relaxed molecular clock analyses of Syngnathiformes result in an average posterior crown age estimate of 104.6 million years ago, with the credible interval ranging between 95.0 and 114.8 million years ago (Ghezelayagh et al. 2022).

  • img-z125-8_03.gif

    Ovalentaria W. L. Smith and T. J. Near in
    Wainwright et al. 2012
    [C. E. Thacker and T. J. Near], converted clade name

  • Definition. The least inclusive crown clade that contains Ambassis urotaenia Bleeker 1852, Mugil cephalus Linnaeus 1758, Embiotoca lateralis Agassiz 1854, Pseudochromis fridmani Klausewitz 1968, Gobiesox maeandricus (C. Girard 1858a), Gillellus semicinctus Gilbert 1890, Polycentrus schomburgkii Müller and Troschel 1848, Pholidichthys leucotaenia Bleeker 1856, Cichla temensis Humboldt in Humboldt and Valenciennes 1821, Labidesthes sicculus (Cope 1865), Gambusia affinis (Baird and Girard 1853), and Oryzias latipes (Temminck and Schlegel 1846). This is a minimum-crown-clade definition.

  • Etymology. From the Latin ovum meaning egg and lentae meaning sticky or tenacious.

  • Registration number. 998.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of 10 concatenated Sanger-sequenced nuclear genes (Wainwright et al. 2012, fig. 2). The phylogenetic resolution of Ovalentaria within Percomorpha is presented in Figure 2, and the phylogenetic relationships of the major lineages of Ovalentaria are presented in Figures 14 and 16.

  • Phylogenetics. Monophyly of Ovalentaria was discovered in early molecular analyses aimed at resolving relationships within Percomorpha (W.-J. Chen et al. 2003; Dettaï and Lecointre 2005; Miya et al. 2005; W. L. Smith and Wheeler 2006; Mabuchi et al. 2007; W. L. Smith and Craig 2007; Kawahara et al. 2008; Setiamarga et al. 2008). A phylogenetic analysis of DNA sequences from four nuclear genes resolved a clade comprising Mugilidae (mullets), Plesiopidae (roundheads), Blennioidei (blennies), Atheriniformes (silversides, needlefishes, and killifishes), Cichlidae (cichlids), Gobiesocidae (clingfishes), and Pomacentridae (damselfishes) (B. Li et al. 2009). A subsequent analysis of 10 exons expanded the clade to include Polycentridae (leaffishes), Pholidichthys (engineer blennies), Embiotocidae (surfperches), Congrogadidae (eel blennies), Pseudochromidae (dottybacks), Gramma and Lipogramma (basslets), and Opistognathidae (jawfishes) (Wainwright et al. 2012). Subsequent molecular analyses consistently support the monophyly of Ovalentaria (Betancur-R, Broughton, et al. 2013; Near et al. 2013; Collins et al. 2015; Betancur-R et al. 2017; Alfaro et al. 2018; Hughes et al. 2018; Ghezelayagh et al. 2022; Mu et al. 2022). Initially, the monophyly of Ovalentaria was discussed in the context of the presence of demersal eggs with adhesive filaments that characterizes many of the lineages in the clade (Breder and Rosen 1966; Semple 1985; Mooi 1990; Wirtz 1993; Britz 1997; Breining and Britz 2000).

  • A morphological phylogenetic analysis of Ovalentaria based on 38 characters scored from the caudal skeleton did not include other percomorph lineages and therefore did not test monophyly of the clade (Thieme et al. 2022). Relationships within Ovalentaria differed from molecular phylogenetic analyses in that Gramma and Lipogramma were resolved as a clade, Pholidichthys and Cichlidae were not resolved as sister lineages, Gobiesocidae and Blennioidei did not form a monophyletic group, and both Blennioidei and Atheriniformes were resolved as paraphyletic (Thieme et al. 2022).

  • Composition. There are currently 5,940 living species of Ovalentaria (Fricke et al. 2023) classified in Atheriniformes and Blenniiformes. Over the past 10 years, 527 new living species of Ovalentaria have been described (Fricke et al. 2023), comprising approximately 8.9% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Ovalentaria are currently limited to features of the caudal skeleton and include (1) fusion of two ural centra to form the compound centrum during development (Thieme et al. 2022), and (2) second uroneural present (Thieme et al. 2022).

  • Synonyms. Blenniiformes (Dornburg and Near 2021; Ghezelayagh et al. 2022) and Ovalentariae (Betancur-R, Broughton, et al. 2013:13) are ambiguous synonyms of Ovalentaria. Stiassnyiformes (B. Li et al. 2009, tbl. 4) is a partial synonym of Ovalentaria.

  • Comments. Ovalentaria is one of the most species-rich named clades of Percomorpha and similarly to nearly every percomorph clade was discovered primarily through molecular phylogenetic analyses (e.g., Wainwright et al. 2012). A study examining the morphology of the caudal skeleton in Ovalentaria illustrates the potential of applying molecular inferred phylogenies with novel results to understanding phenotypic evolution in large inclusive clades of Percomorpha (Thieme et al. 2022). The name Ovalentaria was selected as the clade name over its synonyms because it seems to be the name most frequently applied to a taxon approximating the named clade.

  • Bayesian relaxed molecular clock analyses of Ovalentaria result in an average posterior crown age estimate of 96.2 million years ago, with the credible interval ranging between 86.2 and 106.0 million years ago (Ghezelayagh et al. 2022).

  • img-z128-3_03.gif

    FIGURE 16.

    Phylogenetic relationships of the major living lineages and fossil taxa of Ovalentaria, Atheriniformes, Atherinoidei, Belonoidei, Cyprinodontoidei, Blenniiformes, and Blennioidei. Filled circles identify the common ancestor of clades with formal names defined in the clade accounts. Open circles highlight clades with informal group names. Fossil lineages are indicated with a dagger (†). Details of the fossil taxa are presented in Appendix 1.

    img-z127-1_03.jpg

    Atheriniformes J. Ferrer Aledo 1930:245

  • Definition. The least inclusive crown clade that contains Oryzias latipes (Temminck and Schlegel 1846), Atherina hepsetus Linnaeus 1758, and Cyprinodon variegatus Lacépède 1803. This is a minimum-crown-clade definition, but the clade is not defined using the PhyloCode.

  • Etymology. From the ancient Greek ἀθερίνη (æθɚɹˈiːnə), which is the name used by ancient authors (e.g., Aristotle and Oppian) in reference to the Mediterranean Sand Smelt, Atherina hepsetus Linnaeus (D. W. Thompson 1947:3–4).

  • Reference phylogeny. A phylogeny inferred from sequences of 989 ultraconserved element loci (Ghezelayagh et al. 2022, fig. S10). Although Atherina hepsetus is not included in the reference phylogeny, it resolves in a clade with other species of Atherina in phylogenetic analyses of Sanger-sequenced mitochondrial and nuclear genes (Sparks and Smith 2004b, fig. 2; Astolfi et al. 2005, fig. 2; Francisco et al. 2008, fig. 2, 2011, fig. 2; Heras and Roldán 2011, fig. 2; Campanella et al. 2015, fig. 2B). See Figure 16 for a phylogeny of the lineages comprising Atheriniformes.

  • Phylogenetics. The delimitation of Atheriniformes that includes Atherinoidei, Belonoidei, and Cyprinodontoidei was first proposed in a pre-Hennigian study of osteology, musculature, and reproductive characters that aimed toward the identification of “a phylogenetically natural group” (Rosen 1964:260). Since this work, the monophyly of Atheriniformes has not been challenged. Analysis of the gill arch skeleton and hyoid apparatus led to the reclassification of Adrianichthyidae (ricefishes) from Cyprinodontoidei to Belonoidei, the discovery that Atherinoidei was not diagnosed by morphological synapomorphies, and the resolution of Belonoidei and Cyprinodontoidei as sister lineages (Rosen and Parenti 1981). Subsequent phylogenetic analyses using morphological characters consistently supported the monophyly of Atheriniformes and the sister lineage relationship between Belonoidei and Cyprinodontoidei (White 1985; Stiassny 1990; L. R. Parenti 1993, 2005; Saeed et al. 1994; Dyer and Chernoff 1996; Dyer H 2006).

  • Several of the earliest molecular phylogenies of Percomorpha resolved Atheriniformes as paraphyletic as a result of the placement of other lineages of Ovalentaria (W.-J. Chen et al. 2003; Dettaï and Lecointre 2005; Miya et al. 2005), but subsequent molecular phylogenetic studies support atheriniform monophyly (Mabuchi et al. 2007; Kawahara et al. 2008; Setiamarga et al. 2008; B. Li et al. 2009; Near, Eytan, et al. 2012; Wainwright et al. 2012; Betancur-R, Broughton, et al. 2013; Near et al. 2013; Eytan et al. 2015; Davis et al. 2016; Smith et al. 2016; Betancur-R et al. 2017; Hughes et al. 2018; Rabosky et al. 2018; Ghezelayagh et al. 2022). Within Atheriniformes, molecular phylogenies have resolved all three possible relationships among Atherinoidei, Belonoidei, and Cyprinodontoidei: Belonoidei and Cyprinodontoidei as sister lineages (Miya et al. 2005; Mabuchi et al. 2007; Kawahara et al. 2008; Setiamarga et al. 2008; Wainwright et al. 2012; Betancur-R, Broughton, et al. 2013; Near et al. 2013; Smith et al. 2016; Hughes et al. 2018; Rabosky et al. 2018), Atherinoidei and Belonoidei as sister lineages (B. Li et al. 2009; Eytan et al. 2015; Ghezelayagh et al. 2022), and Atherinoidei and Cyprinodontoidei as sister lineages (Davis et al. 2016; Betancur-R et al. 2017). Node support for these relationships is typically low, and changes in taxon sampling for similar sets of sampled genes seem to affect the resolution of relationships within Atheriniformes (e.g., Betancur-R, Broughton, et al. 2013; Betancur-R et al. 2017). While there is strong support from both morphological and molecular data for monophyly of Atheriniformes, there remains uncertainty in the relationships among Atherinoidei, Belonoidei, and Cyprinodontoidei.

  • Composition. There are currently 2,126 living species of Atheriniformes (Fricke et al. 2023) classified in Atherinoidei, Belonoidei, and Cyprinodontoidei. Over the past 10 years, 259 new living species of Atheriniformes have been described (Fricke et al. 2023), comprising approximately 12.2% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Atheriniformes include (1) separation of afferent and efferent circulation during development (Rosen and Parenti 1981; L. R. Parenti 1993, 2005; Wiley and Johnson 2010), (2) a restricted lobular type of testis, in which the spermatogonia are present at the lobule ends only rather than throughout the entire length of the lobule (Rosen and Parenti 1981; L. R. Parenti 1993, 2005; L. R. Parenti and Grier 2004; Wiley and Johnson 2010; Uribe et al. 2014), (3) protrusible upper jaw mechanism with palatomaxillary ligaments crossed and with maxillary ligament to the cranium (Rosen and Parenti 1981), (4) dermal and endochondral disclike ethmoid ossifications (Rosen and Parenti 1981; L. R. Parenti 1993, 2005; Wiley and Johnson 2010), (5) medial hooklike projection and ventral flange on fifth ceratobranchial (Stiassny 1990; L. R. Parenti 1993, 2005; Wiley and Johnson 2010), (6) supraneurals absent (Stiassny 1990; L. R. Parenti 1993, 2005; Wiley and Johnson 2010), (7) infraorbital series consisting of lacrimal, dermosphenotic, and two or fewer anterior infraorbital bones (Rosen and Parenti 1981; L. R. Parenti 1993, 2005; Wiley and Johnson 2010), (8) dorsal portion of gill arch with large fourth epibranchial as the supporting bone (Rosen and Parenti 1981; L. R. Parenti 1993, 2005; Wiley and Johnson 2010), (9) fourth pharyngobranchial absent in dorsal gill arch (Rosen and Parenti 1981; L. R. Parenti 1993, 2005; Wiley and Johnson 2010), (10) saccus vasculosus absent (Tsuneki 1992; L. R. Parenti 2005; Wiley and Johnson 2010), (11) coupling during mating (L. R. Parenti 1993, 2005; Wiley and Johnson 2010), (12) distal end of pleural rib and lateral process of pelvic bone in close association and sometimes attached with a ligament (L. R. Parenti 1993, 2005; Wiley and Johnson 2010), (13) supracleithrum reduced or absent (L. R. Parenti 1993, 2005; Wiley and Johnson 2010), (14) superficial (A1) division of adductor mandibulae with two tendons, one inserting on maxilla, second inserting on lacrimal (L. R. Parenti 1993, 2005; Wiley and Johnson 2010), (15) olfactory sensory epithelium arranged in sensory islets (L. R. Parenti 1993, 2005; Wiley and Johnson 2010), (16) fluid (rather than granular) egg yolk (L. R. Parenti and Grier 2004; L. R. Parenti 2005; Wiley and Johnson 2010), (17) caudal fin supported by three preural centra (Thieme et al. 2022), (18) lower hypural plate fused with compound centrum (Thieme et al. 2022), (19) uroneural fused with compound centrum (Thieme et al. 2022), (20) haemal arch of preural centrum 2 fused with its centrum (Thieme et al. 2022), and (21) absence of interhaemal spine cartilage 2 (Thieme et al. 2022).

  • Synonyms. Atherinomorpha (Greenwood et al. 1966:397; Rosen 1973:510, fig. 129; Rosen and Parenti 1981:23; J. S. Nelson et al. 2016:353–354) and Atherinomorphae (Wiley and Johnson 2010:154; Betancur-R, Broughton, et al. 2013, fig. 8; Betancur-R et al. 2017:25) are ambiguous synonyms of Atheriniformes.

  • Comments. Atheriniformes was applied as the name of a taxonomic group that included species classified in Atherinoidei, Belonoidei, and Cyprinodontoidei (Rosen 1964; Greenwood et al. 1966:397–398).

  • The earliest fossils of Atheriniformes are all from the Ypresian (56.0–48.1 Ma) of Italy and include the pan-exocoetid †Rhamphexocoetus (Appendix 1; Bannikov et al. 1985) and the atherinoid †Latellagnathus (Bannikov et al. 1985; Bannikov 2008, 2014b; Carnevale et al. 2014). Bayesian relaxed molecular clock analyses of Atheriniformes result in an average posterior crown age estimate of 87.5 million years ago, with the credible interval ranging between 76.8 and 97.2 million years ago (Ghezelayagh et al. 2022).

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    Atherinoidei P. Bleeker 1859:xxiv

  • Definition. The least inclusive crown clade that contains Atherinella panamensis Steindachner 1875, Atherinopsis californiensis C. Girard 1854, Atherina hepsetus Linnaeus 1758, and Atherion elymus Jordan and Starks 1901. This is a minimum-crown-clade definition, but the clade is not defined using the PhyloCode.

  • Etymology. From the ancient Greek ἀθερίνη (æθɚɹˈiːnə), which is the name for the Mediterranean Sand Smelt, Atherina hepsetus Linnaeus, used by Aristotle and Oppian (D. W. Thompson 1947:3–4).

  • Reference phylogeny. A phylogeny inferred from a dataset comprising eight Sanger-sequenced mtDNA and nuclear genes (Campanella et al. 2015, fig. 2). Although Atherina hepsetus is not included in the reference phylogeny, it resolves in a clade with other species of Atherina in phylogenetic analyses of Sanger-sequenced mitochondrial and nuclear genes (e.g., Campanella et al. 2015, fig. 2B). Phylogenetic relationships of the major lineages of Atherinoidei are presented in Figure 16.

  • Phylogenetics. Subsequent to the delimitation of Atherinoidei (Rosen 1964), several morphological studies did not support the monophyly of the group (Rosen and Parenti 1981; L. R. Parenti 1984, 1989, 1993; Ivantsoff et al. 1987; Saeed et al. 1994); however, studies based on adult and larval morphology provided evidence for the monophyly of the lineage (White et al. 1984; Dyer and Chernoff 1996; Aarn and Ivantsoff 1997). Molecular phylogenetic studies consistently resolve Atherinoidei as monophyletic (Setiamarga et al. 2008; Bloom et al. 2012; Betancur-R, Broughton, et al. 2013; Near et al. 2013; Campanella et al. 2015; Betancur-R et al. 2017; Hughes et al. 2018; Rabosky et al. 2018; Ghezelayagh et al. 2022).

  • Morphological and molecular phylogenetic analyses are congruent in resolving Atherinopsidae (New World silversides) as the sister lineage of all other Atherinoidei (Aarn and Ivantsoff 1997; Bloom et al. 2012; Near et al. 2013; Campanella et al. 2015; Betancur-R et al. 2017; Ghezelayagh et al. 2022). One area of incongruence among phylogenetic analyses is the support for Notocheirus hubbsi (Surf Silverside) and species of Iso (surf sardines) as sister lineages in a morphological study (Dyer and Chernoff 1996); however, Notocheirus is nested well within Atherinopsidae and Iso is resolved as the sister lineage of a clade containing Atherinidae (silversides), Bedotiidae (Madagascar rainbowfishes), Melanotaeniidae (rainbowfishes), Telmatherinidae (Celebes rainbowfishes), and Pseudomugilidae (blue eyes) in molecular phylogenies (Bloom et al. 2012, 2013; Campanella et al. 2015; Rabosky et al. 2018; Ghezelayagh et al. 2022).

  • Phylogenetic analyses of Sanger-sequenced mtDNA and nuclear genes result in the paraphyly of Melanotaeniidae because Cairnsichthys is resolved as the sister lineage all other sampled species of Telmatherinidae and Pseudomugilidae (Bloom et al. 2012; Campanella et al. 2015; Rabosky et al. 2018); however, Melanotaeniidae is monophyletic in morphological and phylogenomic analyses (Aarn and Ivantsoff 1997; Aarn et al. 1998; Ghezelayagh et al. 2022). Following conclusions from a morphological phylogenetic analysis (Dyer and Chernoff 1996), Nelson et al. (2016:358–360) treat Bedotiidae, Pseudomugilidae, and Telmatherinidae as lineages of Melanotaeniidae.

  • A molecular phylogeny resolves Atherion (pricklenose silversides) and Phallostethidae (priapiumfishes) as sister lineages (Campanella et al. 2015). To date, there are no molecular data available for Dentatherina merceri (Mercer's Tusked Silverside), but several morphological studies place it as the sister lineage of Phallostethidae (L. R. Parenti 1984; Dyer and Chernoff 1996; Aarn and Ivantsoff 1997). This has prompted the classification of D. merceri in Phallostethidae (Dyer and Chernoff 1996; Aarn and Ivantsoff 1997; J. S. Nelson 2006:273); however, the group name Dentatherinidae, including only D. merceri, is endorsed by others (Ivantsoff et al. 1987; J. S. Nelson et al. 2016:360–361). Because D. merceri is convincingly resolved as the sister lineage of a clade containing all other priapiumfishes, we include it in Phallostethidae as an optimal reflection of phylogenetic relationships and an effort to reduce redundant group names in the classification of ray-finned fishes.

  • Composition. There are currently 385 living species of Atherinoidei (Fricke et al. 2023) classified in Atherinidae, Atherinopsidae, Atherion, Bedotiidae, Iso, Melanotaeniidae, Phallostethidae, Pseudomugilidae, and Telmatherinidae. Over the past 10 years, there have been 38 new species of Atherinoidei described (Fricke et al. 2023), comprising 9.9% of the species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Atherinoidei include (1) preanal length of flexion larvae short, approximately 33% of body length (White et al. 1984; Wiley and Johnson 2010), (2) single row of melanophores on dorsal midline of larvae (White et al. 1984; L. R. Parenti 2005; Wiley and Johnson 2010), (3) ventral face of vomer concave (Dyer and Chernoff 1996; Wiley and Johnson 2010), (4) adductor mandibulae A1 with long tendon to lacrimal (Dyer and Chernoff 1996; Wiley and Johnson 2010), (5) two anterior infraorbital bones (Dyer and Chernoff 1996; L. R. Parenti 2005; Wiley and Johnson 2010), (6) presence of pelvic rib ligament (Dyer and Chernoff 1996; Wiley and Johnson 2010), (7) pelvic plate does not extend to anterior tip of longitudinal shaft (Dyer and Chernoff 1996; Wiley and Johnson 2010), and (8) presence of a flexible second dorsal fin (Dyer and Chernoff 1996; Wiley and Johnson 2010).

  • Synonyms. Atherinidae (Jordan and Hubbs 1919:12–19; Schultz 1948:2–3) and Atheriniformes(Saeedetal.1994:47–48;DyerandChernoff 1996, tbl. 1; Wiley and Johnson 2010:155; Betancur-R, Broughton, et al. 2013, fig. 3; J. S. Nelson et al. 2016:354–355; Betancur-R et al. 2017:25) are ambiguous synonyms of Atherinoidei.

  • Comments. In the mid-20th century, Atherinoidei was applied as the name of a group containing Atherinidae, Bedotiidae, Isonidae, Melanotaeniidae, Phallostethidae, and Pseudomugilidae (Rosen 1964; Greenwood et al. 1966).

  • The earliest fossil taxa of Atherinoidei are all from the Ypresian (56.0–48.1 Ma) and include the otolith taxon †‘Atherinidarum’ from France and India (Nolf 1988; Nolf et al. 2006) and the skeletal fossils †Rhamphognathus, †Latellagnathus, and †Mesogaster from Italy (Bannikov 2008, 2014b; Carnevale et al. 2014). Bayesian relaxed molecular clock analyses of Atherinoidei result in an average posterior crown age estimate of 71.0 million years ago, with the credible interval ranging between 56.5 and 84.4 million years ago (Ghezelayagh et al. 2022).

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    Belonoidei E. Postel 1959:150

  • Definition. The least inclusive crown clade that contains Adrianichthys oophorus (Kottelat 1990), Xenentodon cancila (Hamilton 1822), Hemiramphus far (Fabricius in Niebuhr 1775), and Belone belone (Linnaeus 1761). This is a minimum-crown-clade definition, but the clade is not defined using the PhyloCode.

  • Etymology. From the ancient Greek βελόνη (bƗl̍αːne͡I) meaning needle, but also the name applied to the Greater Pipefish (Syngnathus acus) and the Garfish (Belone belone) in the biological writings of Aristotle (D. W. Thompson 1947:29–32).

  • Reference phylogeny. A phylogeny of 123 species of Belonoidei inferred from a supermatrix of 27 nuclear and mitochondrial genes (Rabosky et al. 2018; J. Chang et al. 2019). The phylogeny is available on the Dryad data repository (Rabosky et al. 2019). Phylogenetic relationships among the major lineages of Belonoidei are presented in Figure 16. The placement of †Rhamphexocoetus in the phylogeny is on the basis of inferences from morphology (Bannikov et al. 1985; Benton et al. 2015).

  • Phylogenetics. Hemiramphidae (halfbeaks), Exocoetidae (flyingfishes), Belonidae (needlefishes), and Scomberesocidae (sauries) were grouped together in early 20th-century classifications (Schlesinger 1909; Regan 1911f). Phylogenetic analysis of morphology led to a delimitation of Belonoidei that includes those lineages plus Adrianichthyidae (ricefishes) (Rosen and Parenti 1981). Subsequent morphological and molecular studies provided additional support for the monophyly of Belonoidei and for the resolution of Adrianichthyidae as the sister lineage to all other belonoids (Collette, McGowen, et al. 1984; L. R. Parenti 1987, 1993, 2008; Miya et al. 2003, 2005; Kawahara et al. 2008; Setiamarga et al. 2008; Near, Eytan, et al. 2012; Wainwright et al. 2012; Near et al. 2013; Davis et al. 2016; Smith et al. 2016; Betancur-R et al. 2017; Hughes et al. 2018; Ghezelayagh et al. 2022; Ding et al. 2023).

  • Phylogenetic analyses of morphological and molecular data motivated changes to the traditional classification of Belonoidei (Lovejoy et al. 2004; Aschliman et al. 2005), but current classifications continue to include paraphyletic groups (J. S. Nelson et al. 2016:363–370; Betancur-R et al. 2017). For example, Belonidae as traditionally delimited is paraphyletic because species classified in Scomberesocidae (sauries), Cololabis, and Scomberesox are nested within Belonidae as the sister lineage of Belone (Lovejoy 2000; Lovejoy et al. 2004; Daane et al. 2021). Cololabis and Scomberesox are now placed in Belonidae (Betancur-R et al. 2017). Hemiramphidae is resolved as paraphyletic in both morphological (Tibbetts 1991; Aschliman et al. 2005) and molecular phylogenetic analyses (Lovejoy 2000; Lovejoy et al. 2004; Betancur-R et al. 2017; Daane et al. 2021; Ghezelayagh et al. 2022; Ding et al. 2023). The paraphyly of Hemiramphidae led to the recognition of Zenarchopteridae (viviparous halfbeaks) as a separate Linnean-ranked taxonomic family (Lovejoy et al. 2004); however, the remaining lineages of Hemiramphidae are paraphyletic relative to Exocoetidae. Three lineages comprise the current delimitation of Hemiramphidae (Lovejoy 2000; Lovejoy et al. 2004; Daane et al. 2021): a clade we refer to with the informal name hyporhamphids that contains Arrhamphus, Chriodorus atherinoides, Hyporhamphus, and Melapedalion breve for which there is no available family-group name (Van der Laan et al. 2014:77); Euleptorhamphus and Rhynchorhamphus that we delimit as Euleptorhamphidae, an elevation of Euleptorhamphinae (Fowler 1934:323); and Hemiramphidae that is limited here to species of Hemiramphus and Oxyporhamphus. The more exclusive Hemiramphidae and Exocoetidae are consistently resolved as sister lineages in molecular phylogenetic analyses (Lovejoy 2000; Lovejoy et al. 2004; Betancur-R et al. 2017; Daane et al. 2021; Ghezelayagh et al. 2022). Morphological phylogenetic analyses result in the resolution of most lineages traditionally classified in Hemiramphidae in a large polytomy with a clade containing Oxyporhamphus and Exocoetidae (Tibbetts1991; Aschliman et al. 2005).

  • Composition. There are currently 292 living species of Belonoidei (Collette 2003, 2004a, 2004b; Bemis and Collette 2019; Collette and Bemis 2019a, 2019b, 2019c; Parin et al. 2019; Fricke et al. 2023) that include Arrhamphus sclerolepis, Chriodorus atherinoides, Melapedalion breve, and species classified in Adrianichthyidae, Belonidae, Euleptorhamphidae, Exocoetidae, Hemiramphidae, Hyporhamphus, and Zenarchopteridae. Fossil Belonoidei include the pan-exocoetid †Rhamphexocoetus volans (Appendix 2; Bannikov et al. 1985). Over the past 10 years, 25 new species of Belonoidei have been described (Fricke et al. 2023), comprising 8.6% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Belonoidei include (1) interarcual cartilage absent (Rosen and Parenti 1981; L. R. Parenti 2005, 2008; Wiley and Johnson 2010), (2) relatively small second and third epibranchials (Rosen and Parenti 1981; L. R. Parenti 2005, 2008; Wiley and Johnson 2010), (3) vertically reoriented second pharyngobranchial (Rosen and Parenti 1981; L. R. Parenti 2005, 2008; Wiley and Johnson 2010), (4) dorsal hypohyal absent (Rosen and Parenti 1981; L. R. Parenti 2005, 2008; Wiley and Johnson 2010), (5) interhyal absent (Rosen and Parenti 1981; L. R. Parenti 1987, 2005, 2008; Wiley and Johnson 2010), (6) upper lobe of caudal fin with fewer principal fin rays than lower lobe (Rosen and Parenti 1981; L. R. Parenti 2005, 2008; Wiley and Johnson 2010), and (7) parietals extremely small or absent (L. R. Parenti 2008; Wiley and Johnson 2010).

  • Synonyms. Beloniformes (Rosen and Parenti 1981:23; Wiley and Johnson 2010:156; Betancur-R, Broughton, et al. 2013, fig. 8; J. S. Nelson et al. 2016:363–370; Betancur-R et al. 2017:25) is an ambiguous synonym of Belonoidei. Synentognathi (Regan 1911f:331–335) and Exocoetoidei (Greenwood et al. 1966:397) are partial synonyms of Belonoidei.

  • Comments. In earlier classifications, Belonoidei is used as a group name for all belonoids to the exclusion of Adrianichthyidae (Nelson 1994:266; Betancur-R et al. 2017). The earliest fossil taxa of Belonoidei are all from the Ypresian (56.0–48.1 Ma) of Italy and include the pan-exocoetid †Rhamphexocoetus and the taxa †“Engraulisevolans and †“Hemiramphusedwardsi of uncertain phylogenetic resolution within the clade (Bannikov et al. 1985; Bannikov 2014b; Carnevale et al. 2014). Bayesian relaxed molecular clock analyses result in an average posterior crown age estimate of the Belonoidei crown of 68.0 million years ago, with the credible interval ranging between 56.8 and 81.2 million years ago (Ghezelayagh et al. 2022). Euleptorhamphidae is a valid family-group name under the International Code of Zoological Nomenclature (Van der Laan et al. 2014:77).

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    Cyprinodontoidei P. Bleeker 1859:xxix

  • Definition. The least inclusive crown clade that contains Cyprinodon variegatus Lacépède 1803, Poecilia velifera (Regan 1914a), Pantanodon stuhlmanni (Ahl 1924), Austrolebias nigripinnis (Regan 1912f), and Aplocheilus lineatus (Valenciennes in Cuvier and Valenciennes 1846). This is a minimum-crown-clade definition, but the clade is not defined using the PhyloCode.

  • Etymology. From the ancient Greek κυπρῖνος (kuːpɹˈiːno͡ʊz), frequently applied to the Eurasian Carp, Cyprinus carpio (D. W. Thompson 1947:135–136), and δών (̍o͡Ʊdαːn) meaning tooth.

  • Reference phylogeny. A phylogeny inferred from DNA sequences of 295 genes captured using anchored hybrid enrichment (Piller et al. 2022, figs. 3–7). Although Cyprinodon variegatus is not included in the reference phylogeny, it resolves in a clade with other species of Cyprinodon in phylogenetic analyses of mtDNA (Echelle et al. 2005, 2006; Martin and Wainwright 2011). Phylogenetic relationships of the major living and fossil lineages of Cyprinodontoidei are presented in Figure 16. The phylogenetic resolutions of the pan-rivulid †Kenyaichthys, the pan-orestiid †Carrionellus, and the pan-valenciids †Francolebias and †Prolebias are on the basis of inferences from morphology (Costa 2011, 2012b; Altner and Reichenbacher 2015).

  • Phylogenetics. The lineages that comprise Cyprinodontoidei were grouped together in many pre-Hennigian classifications of teleost fishes (e.g., Garman 1895), but were thought to be related to such disparate lineages as Esocidae and Amblyopsidae (T. N. Gill 1872; Boulenger 1904a; Goodrich 1909:400–401; Regan 1909a, 1911g; Hubbs 1924; Gosline 1963a). Subsequent studies identified Atheriniformes as a clade containing Cyprinodontoidei, Atherinoidei, and Belonoidei (Rosen 1964; Greenwood et al. 1966; Rosen and Parenti 1981). Morphological and molecular phylogenetic analyses of relationships within Cyprinodontoidei are broadly congruent in supporting monophyly of the lineage and the resolution of two clades: the aplocheiloids and cyprinodontoids (L. R. Parenti 1981; Costa 1998, 2012a, 2012b; Hertwig 2008; Pohl et al. 2015; Helmstetter et al. 2016; Costa et al. 2017; Reznick et al. 2017; Amorim and Costa 2018; Bragança et al. 2018; Ghezelayagh et al. 2022; Piller et al. 2022).

  • Relationships among the aplocheiloids, including Aplocheilidae (Asian rivulines), Nothobranchiidae (African rivulines), and Rivulidae (New World rivulines), vary among different phylogenetic analyses. Studies using mtDNA and morphology resolve the traditional delimitation of Aplocheilidae (e.g., L. R. Parenti 1981) as paraphyletic (Murphy and Collier 1997; Costa 2004, 2012a, 2012b), with African lineages and the South American Rivulidae forming a clade that is the sister lineage of the Asian-Malagasy Aplocheilidae (sensu stricto). Because of the apparent paraphyly of Aplocheilidae, the African aplocheiloid lineages are now classified in Nothobranchiidae (Costa 2004, 2016). Subsequent phylogenetic analyses of morphology (Hertwig 2008), Sanger-sequenced mtDNA and nuclear genes (Pohl et al. 2015; Costa et al. 2017; Reznick et al. 2017; Amorim and Costa 2018; Bragança et al. 2018), and phylogenomic datasets (Ghezelayagh et al. 2022; Piller et al. 2022) resolve Rivulidae as the sister lineage of a clade containing Aplocheilidae and Nothobranchiidae.

  • Molecular phylogenies resolve Pantanodon (spine killifishes) as the sister lineage of all other cyprinodontoids (Pohl et al. 2015; Bragança et al. 2018; Piller et al. 2022). The remaining cyprinodontoid lineages resolve into three clades (Amorim and Costa 2018; Bragança and Costa 2019; Ghezelayagh et al. 2022; Piller et al. 2022): (1) Cubanichthyidae (Caribbean killifishes), Cyprinodontidae (pupfishes), Fundulidae (topminnows), Goodeidae (goodeids), and Profundulidae (Middle American killifishes) (Webb et al. 2004; Reznick et al. 2017); (2) Anablepidae (four-eyed fishes), Fluviphylax (American lampeyes), and Poeciliidae (livebearers) (Reznick et al. 2017; Bragança and Costa 2018); and (3) Aphaniidae (Asian killifishes), Procatopodidae (African lampeyes), Orestiidae (Andean pupfishes), and Valencia (toothcarps) (A. Parker and Kornfield 1995; Pohl et al. 2015; Helmstetter et al. 2016; Reznick et al. 2017; Bragança and Costa 2019). The traditional delimitations of Cyprinodontidae and Poeciliidae (L. R. Parenti 1981; Ghedotti 2000) are paraphyletic. Fluviphylax, Pantanodon, and Procatopodidae do not share common ancestry with Poeciliidae; Aphaniidae, Cubanichthyidae, and Orestiidae are distantly related to Cyprinodontidae (Freyhof et al. 2017; Bragança and Costa 2019; Piller et al. 2022).

  • Composition. There are currently 1,449 living species of Cyprinodontoidei (Fricke et al. 2023) classified in Aplocheilidae, Nothobranchiidae, Rivulidae, Anablepidae, Aphaniidae, Cubanichthyidae, Cyprinodontidae, Fluviphylax, Fundulidae, Goodeidae, Orestiidae, Pantanodontidae (Meinema and Huber 2023), Poeciliidae, Profundulidae, Procatopodidae, and Valencia. Fossil taxa include the pan-rivulid †Kenyaichthys kipkechi (Altner and Reichenbacher 2015), the pan-orestiid †Carrionellus diumortuus (Costa 2011), and the pan-valenciids †Francolebias aymardi and †Prolebias stenoura (J. Gaudant 1988; Costa 2012b). Details of the ages and locations of the fossil taxa are presented in Appendix 1. Over the past 10 years, 196 new species of Cyprinodontoidei have been described (Fricke et al. 2023), comprising 13.5% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Cyprinodontoidei include (1) caudal fin endoskeleton with one epural symmetrically opposing parhypural (L. R. Parenti 1981; Rosen and Parenti 1981; Costa 2012a), (2) caudal fin unlobed, truncate or rounded (L. R. Parenti 1981; Rosen and Parenti 1981; Costa 1998), (3) first rib attached to second rather than third vertebra (L. R. Parenti 1981; Costa 1998), (4) pectoral fin set low on body, with large scalelike postcleithrum (L. R. Parenti 1981; Rosen and Parenti 1981; Costa 1998), (5) elongate interarcual cartilage joining expanded base of first epibranchial with shaft of second pharyngobranchial (Rosen and Parenti 1981), (6) presence of anterior expansion on the alveolar arm of premaxilla (Costa 1998), (7) tendon of the A1 division of adductor mandibulae attached to the lacrimal (Costa 1998; Hertwig 2008), (8) dorsal edge of mesopterygoid reduced (Costa 1998), (9) urohyal deep (Costa 1998), (10) ventral process of lateral portion of epibranchial 2 absent (Costa 1998), (11) mesethmoid slightly anterior to lateral ethmoid (Costa 1998), (12) anteromedial process of pelvic girdle absent (Costa 1998), (13) subdivision of A1 adductor mandibulae into two heads (Hertwig 2008), (14) many muscle fibers arising from the tendon or aponeurosis of the A2 /A3 adductor mandibulae (Hertwig 2008), (15) the A2 /A3 adductor mandibulae subdivided into three distinct heads by the ramus mandibularis (Hertwig 2008), (16) a separate section of the adductor mandibulae (AωQ) originates with a single tendon from the medial face of the quadrate (Hertwig 2008), (17) adductor arcus palatini inserts medially on the mesopterygoid (Hertwig 2008), (18) epural with bladelike shape (Costa 2012a), (19) caudal fin rays continuously arranged between upper and lower hypural plates (Costa 2012a), (20) distal tip of well-developed preural vertebra 2 acting in support of caudal fin rays (Costa 2012a), (21) stegural minute (Costa 2012a), (22) neural spine of preural vertebra 2 wider than neural spines of preural vertebrae 4 and 5 (Costa 2012a), and (23) complete ankylosis of upper hypurals and compound caudal centrum (Costa 2012a).

  • Synonyms. Cyprinodontiformes (L. R. Parenti 1981:462–463, 1993, tbl. 2; Rosen and Parenti 1981:23; Wiley and Johnson 2010:157; Betancur-R, Broughton, et al. 2013, fig. 8; J. S. Nelson et al. 2016:369–380; Betancur-R et al. 2017:26) is an ambiguous synonym of Cyprinodontoidei. Microcyprini (Regan 1911g:321–322) is a partial synonym of Cyprinodontoidei.

  • Comments. In the mid-20th century, Cyprinodontoidei was applied as the name of a group containing Adrianichthyidae, Anablepidae, Cyprinodontidae, Goodeidae, and Poeciliidae (Rosen 1964; Greenwood et al. 1966).

  • Time-calibrated molecular phylogenies estimate divergence times for clades in Cyprinodontoidei that are too young for Gondwanan fragmentation to explain the disjunct geographic distribution of Aplocheilidae (Near et al. 2013; Amorim and Costa 2018; Hughes et al. 2018; Ghezelayagh et al. 2022; Piller et al. 2022). Initial phylogenetic analyses of mtDNA and morphological characters (Murphy and Collier 1997; Costa 2004, 2012a, 2012b) resolved Nothobranchiidae and Rivulidae as sister lineages to the exclusion of Aplocheilidae, a relationship consistent with vicariance-driven diversification resulting from Gondwanan fragmentation. However, both the consistent resolution of Aplocheilidae and Nothobranchiidae as sister lineages (e.g., Amorim and Costa 2018; Piller et al. 2022) and relaxed molecular clock age estimates that date the diversification of Cyprinodontoidei to the latest part of the Cretaceous (e.g., Amorim and Costa 2018; Ghezelayagh et al. 2022; Piller et al. 2022) contradict the Gondwanan vicariance scenario.

  • Bayesian relaxed molecular clock analyses of Cyprinodontoidei result in an average posterior crown age estimate of 76.2 million years ago, with the credible interval ranging between 65.0 and 88.6 million years ago (Ghezelayagh et al. 2022).

  • img-z135-7_03.gif

    Blenniiformes P. Bleeker 1859:xxv
    [C. E. Thacker and T. J. Near], converted clade name

  • Definition. The most inclusive crown clade that contains Lamprologus callipterus Boulenger 1906, Chromis chromis (Linnaeus 1758), Crenimugil crenilabis (Forsskål in Niebuhr 1775), Embiotoca jacksoni Agassiz 1853, Gobiesox maeandricus (C. Girard 1858a), Scartella cristata (Linnaeus 1758), Blennius ocellaris Linnaeus 1758, and Gibbonsia metzi Hubbs 1927, but not Atherina presbyter Cuvier 1829. This is a minimum-crown-clade definition with an external specifier.

  • Etymology. From the ancient Greek βλέννoς (bl̍εno͡Ʊz) used in reference to blennies by ancient Mediterranean authors and also meaning slime or spittle (D. W. Thompson 1947:32–33). The suffix is from the Latin forma meaning form, figure, or appearance.

  • Registration number. 956.

  • Reference phylogeny. A phylogeny inferred from sequences of 989 ultraconserved element (UCE) loci (Ghezelayagh et al. 2022, fig. S11). Although Blennius ocellaris is not included in the reference phylogeny, it resolves in a clade with other species of Blenniidae in phylogenetic analyses of Sanger-sequenced mitochondrial and nuclear genes (Almada et al. 2005, fig. 1; Hundt et al. 2014, fig. 2; Hundt and Simons 2018, figs. 4–6; Vecchioni et al. 2019, fig. 1). Phylogenetic relationships of the major lineages of Blenniiformes are presented in Figure 16. Placement of the fossil pan-pomacentrid †Chaychanus in the phylogeny is on the basis of analysis of morphological characters (Cantalice et al. 2022).

  • Phylogenetics. Monophyly of Blenniiformes was supported in early molecular analyses, but with limited taxon sampling (W. L. Smith and Wheeler 2006; Kawahara et al. 2008). The first resolution of blenniiform monophyly with strong support was a phylogenomic analysis of UCE loci (Ghezelayagh et al. 2022). Within Blenniiformes molecular analyses resolve a clade containing Cichlidae, Pholidichthys, and Polycentridae (Betancur-R et al. 2017; Ghezelayagh et al. 2022; Astudillo-Clavijo et al. 2023), with Cichlidae and Pholidichthys consistently resolved as sister lineages (Wainwright et al. 2012; Friedman, Keck, et al. 2013; Near et al. 2013; Collins et al. 2015; Eytan et al. 2015; Betancur-R et al. 2017; Rabosky et al. 2018; Ghezelayagh et al. 2022; Astudillo-Clavijo et al. 2023). Previous morphological studies led to differing conclusions regarding the relationships of Mugilidae within Percomorpha: analysis of branchial musculature supported a hypothesis that Mugilidae and Atheriniformes are sister lineages (Stiassny 1990), but analysis of pelvic girdle morphology suggested a phylogenetic relationship of mullets with “higher” percomorphs (Stiassny 1993). Both of these analyses were conducted in the context of an Acanthopterygii that placed Atheriniformes outside of Percomorpha (Rosen 1973; Rosen and Parenti 1981; Lauder and Liem 1983), so these seemingly inconsistent conclusions from two different anatomical systems seem to be clarified in the context of a phylogeny in which Atheriniformes is nested within Percomorpha (G. D. Johnson and Patterson 1993; Miya et al. 2003). In some molecular phylogenies, Mugilidae is resolved as either the sister lineage of Embiotocidae or Ambassidae (Asiatic glassfishes) (Wainwright et al. 2012; Near et al. 2013; Collins et al. 2015; Betancur-R et al. 2017; Hughes et al. 2018; Ghezelayagh et al. 2022). Congrogadidae is distantly related to Pseudochromidae in molecular phylogenies (Near et al. 2013; Betancur-R et al. 2017; Ghezelayagh et al. 2022), despite being well nested in Pseudochromidae in phylogenetic analyses of egg morphology, osteology, and external morphological characters (Godkin and Winterbottom 1985; Mooi 1990; A. C. Gill 2013).

  • A notable result of molecular phylogenetic analyses of Blenniiformes is the consistent resolution of a clade containing Gramma, Opistognathidae, Gobiesocidae, and Blennioidei, but exclusive of Lipogramma (Wainwright et al. 2012; Near et al. 2013; Collins et al. 2015; Eytan et al. 2015; Betancur-R et al. 2017; Hughes et al. 2018; Ghezelayagh et al. 2022). Grammatidae traditionally included Gramma and Lipogramma (G. D. Johnson 1984; J. S. Nelson 1984:281), and morphology of the adductor mandibulae muscles and a phylogenetic analysis of 38 caudal fin skeleton characters offers evidence for monophyly of Grammatidae (A. C. Gill and Mooi 1993; Thieme et al. 2022); however, Lipogramma and Gramma are not resolved as a monophyletic group in phylogenetic analyses of Sanger-sequenced mtDNA and nuclear genes (Betancur-R et al. 2017). Gobiesocidae and Blennioidei are resolved as sister lineages in many molecular phylogenetic studies (W.-J. Chen et al. 2003; Dettaï and Lecointre 2005; Miya et al. 2005; Mabuchi et al. 2007; Kawahara et al. 2008; Setiamarga et al. 2008; Wainwright et al. 2012; Lin and Hastings 2013; Near et al. 2013; Collins et al. 2015; Eytan et al. 2015; Smith et al. 2016; Betancur-R et al. 2017; Fricke et al. 2017; Hughes et al. 2018; Ghezelayagh et al. 2022), supporting conclusions from morphological analyses of gill arch musculature and skeletal anatomy (Rosen and Patterson 1990; Springer and Johnson 2004; Springer and Orrell 2004).

  • Composition. There are currently 3,814 living species of Blenniiformes (Fricke et al. 2023) classified in Ambassidae, Blennioidei, Cichlidae, Congrogadidae, Embiotocidae, Gobiesocidae, Gramma, Lipogramma, Mugilidae, Opistognathidae, Pholidichthys, Plesiopidae, Polycentridae, Pomacentridae, and Pseudochromidae. Fossil blenniiforms include the pan-pomacentrid †Chaychanus gonzalezorum (Appendix 1; Cantalice et al. 2020). Over the past 10 years, 268 living species of Blenniiformes have been described (Fricke et al. 2023), comprising approximately 7.0% of the living species diversity in the clade.

  • Diagnostic apomorphies. There are no known morphological apomorphies for Blenniiformes.

  • Synonyms. There are no synonyms of Blenniiformes.

  • Comments. Alternative classifications apply the group name Blenniiformes to a less inclusive clade we define as Blennioidei (Lin and Hastings 2013; Betancur-R et al. 2017). The earliest fossil blenniiform is the pan-pomacentrid †Chaychanus gonzalezorum from the Danian (66.0–61.7 Ma) of Mexico (Cantalice et al. 2020). Bayesian relaxed molecular clock analyses of Blenniiformes result in an average posterior crown age estimate of 88.7 million years ago, with the credible interval ranging between 77.2 and 100.5 million years ago (Ghezelayagh et al. 2022).

  • img-z137-5_03.gif

    Blennioidei P. Bleeker 1853a:114
    [C. E. Thacker and T. J. Near], converted clade name

  • Definition. The least inclusive crown clade that contains Lepidonectes corallicola (Kendall and Radcliffe 1912), Dactyloscopus lacteus (Myers and Wade 1946), Blennius ocellaris Linnaeus 1758, and Gibbonsia metzi Hubbs 1927. This is a minimum-crown-clade definition.

  • Etymology. Derived from the ancient Greek βλέννoς (bl̍εno͡Ʊz) used in reference to blennies by ancient Mediterranean authors and also meaning slime or spittle (D. W. Thompson 1947:32–33).

  • Registration number. 957.

  • Reference phylogeny. A phylogeny inferred from sequences of 989 ultraconserved element loci (Ghezelayagh et al. 2022, fig. S11). Although Blennius ocellaris is not included in the reference phylogeny, it resolves in a clade with other species of Blenniidae in phylogenetic analyses of Sanger-sequenced mitochondrial and nuclear genes (e.g., Vecchioni et al. 2019, fig. 1). See Figure 16 for a phylogeny of the lineages comprising Blennioidei.

  • Phylogenetics. Prephylogenetic hypotheses of the relationships of Blennioidei include many disparately related lineages such as Ammodytidae, Congrogadidae, Notothenioidei, Ophidiiformes, Uranoscopidae, and Zoarcoidei (Regan 1912b; Jordan 1923:228–238; Gosline 1968). The delimitation of Blennioidei presented here was first proposed in studies investigating the systematics of Pholidichthys and Clinidae (Springer and Freihofer 1976; George and Springer 1980) and validated in a review of morphological evidence for blennioid monophyly (Springer 1993). Morphological apomorphies were presented for each of the lineages of Blennioidei, but there is no morphological evidence for the monophyly of Labrisomidae (labrosomid blennies) (Springer 1993). The shape of the cartilage of the third infrapharyngobranchials was presented as a possible synapomorphy for a clade within Blennioidei containing Chaenopsidae (true blennies), Dactyloscopidae (sand stargazers), Labrisomidae, and Clinidae (kelp blennies) (J. T. Williams 1990; Springer 1993).

  • Blennioidei is resolved as monophyletic in morphological (Springer and Orrell 2004) and molecular phylogenetic analyses (Lin and Hastings 2013; Near et al. 2013; Betancur-R et al. 2017; Rabosky et al. 2018; Ghezelayagh et al. 2022). Phylogenetic relationships within Blennioidei resulting from morphological and molecular analyses are congruent. A phylogeny based on dorsal gill arch morphology resolved a paraphyletic Tripterygiidae (triplefin blennies) as successive branching lineages with Lepidoblennius as the sister lineage of all other blennioids and Blenniidae (combtooth blennies) as the sister lineage to a clade containing Clinidae, Chaenopsidae, Dactyloscopidae, and Labrisomidae (Springer and Orrell 2004). Molecular phylogenetic analyses resulted in a very similar phylogeny, except Tripterygiidae is monophyletic and relationships within the clade containing Clinidae, Labrisomidae (sensu stricto), Calliclinus, Chaenopsidae (sensu stricto), and Dactylopteridae are fully resolved (Lin and Hastings 2013; Near et al. 2013; Betancur-R et al. 2017; Rabosky et al. 2018; Ghezelayagh et al. 2022).

  • Molecular phylogenetic analyses of Blennioidei with dense taxon sampling reveal that Chaenopsidae and Labrisomidae are paraphyletic (Lin and Hastings 2013; Rabosky et al. 2018). Stathmonotus, traditionally classified in Chaenopsidae, is phylogenetically nested in Labrisomidae. Neoclinini, containing Neoclinus and Mccoskerichthys and traditionally classified in Chaenopsidae, and Cryptotremini, traditionally classified in Labrisomidae, are resolved as successive branching sister lineages to a clade that contains Labrisomidae (sensu stricto), Chaenopsidae (sensu stricto), and Dactyloscopidae. Calliclinus, traditionally classified in Cryptotremini and Labrisomidae, is the sister lineage of the inclusive clade containing Neoclinini, Cryptotremini, Labrisomidae (sensu stricto), Chaenopsidae (sensu stricto), and Dactyloscopidae (Lin and Hastings 2013; Rabosky et al. 2018). There are available family group-names for Calliclinus, Neoclinini, and Cryptotremini (Van der Laan et al. 2014), but we leave the establishment of taxonomic families for these lineages to future research.

  • Composition. There are currently 948 living species of Blennioidei (Fricke et al. 2023) classified in Blenniidae, Calliclinus, Chaenopsidae, Clinidae, Cryptotremini, Dactyloscopidae, Labrisomidae, Neoclinini, and Tripterygiidae. Over the past 10 years, 24 new living species of Blennioidei have been described, comprising 2.5% of the living species diversity in the clade (Fricke et al. 2023).

  • Diagnostic apomorphies. Morphological apomorphies for Blennioidei include (1) first pharyngobranchial cartilaginous or absent (Springer 1993; Wiley and Johnson 2010), (2) second and fourth pharyngobranchials absent (Springer 1993; Wiley and Johnson 2010), (3) uncinate process or associated interarcual cartilage of first epibranchial absent (Springer 1993; Wiley and Johnson 2010), (4) unique pelvic girdle with bean-shaped pelvis (Springer 1993; Wiley and Johnson 2010), (5) unique, simplified caudal fin (Springer 1993; Wiley and Johnson 2010), (6) neural spines lacking on first vertebrae or several of the anteriormost vertebrae (G. D. Johnson 1993; Wiley and Johnson 2010), (7) first external levator and fourth transversus ventralis absent (Springer and Orrell 2004; Wiley and Johnson 2010), (8) proximal pectoral fin radials longer than wide (Lin and Hastings 2013), (9) unbranched pectoral fin rays (Lin and Hastings 2013), and (10) haemal arch of preural centrum 2 fused with its centrum (Thieme et al. 2022).

  • Synonyms. Blenniicae (Hubbs 1952:51, fig. 1) andBlenniiformes(WileyandJohnson2010:160; J. S. Nelson et al. 2016:346; Betancur-R et al. 2017:26) are ambiguous synonyms of Blennioidei. Blenniiformes (Betancur-R, Broughton, et al. 2013, fig. 8) is a partial synonym of Blennioidei.

  • Comments. The name Blennioidei has long been applied to a group that includes Blenniidae, Chaenopsidae, Clinidae, Dactyloscopidae, Labrisomidae, and Tripterygiidae (Springer and Freihofer 1976; George and Springer 1980; Springer 1993; Hastings and Springer 2009). Since the mid-20th century (Hubbs 1952; Springer and Freihofer 1976; George and Springer 1980), the monophyly of Blennioidei has never been seriously questioned; however, the close relationship between Blennioidei, Opistognathidae, Grammatidae, Embiotocidae, Pomacentridae, and Pseudochromidae is a novel phylogenetic resolution derived from analyses of molecular data (Wainwright et al. 2012; Ghezelayagh et al. 2022). The lineages not currently placed in Linnaean families are listed with generic and tribe names in the classification outlined in Appendix 2 and in the Constituent lineages section below.

  • The earliest fossil Blennioidei is the otolith species †Exallias vectensis from the Ypresian (56.0–48.1 Ma) of France (Nolf 1972; Nolf and Lapierre 1979). The earliest skeletal fossils of Blennioidei are from the Serravallian (13.82–11.63 Ma) of Azerbaijan, Bosnia, Croatia, and Moldova (Anđelković 1989; Bannikov 1998). Bayesian relaxed molecular clock analyses of Blennioidei result in an average posterior crown age estimate of 48.5 million years ago, with the credible interval ranging between 38.6 and 60.2 million years ago (Ghezelayagh et al. 2022).

  • img-z139-2_03.gif

    Carangiformes D. S. Jordan 1923:183
    [C. E. Thacker and T. J. Near], converted clade name

  • Definition. The least inclusive crown clade that contains Centropomus medius Günther 1864b, Polynemus melanochir Valenciennes in Cuvier and Valenciennes (1831), Psettodes erumei (Bloch and Schneider 1801), Pleuronichthys cornutus (Temminck and Schlegel 1846), Xiphias gladius Linnaeus 1758, Caranx melampygus Cuvier in Cuvier and Valenciennes (1833), and Caranx melampygus (Linnaeus 1766). This is a minimum-crown-clade definition.

  • Etymology. From the French carangue, referring to a Caribbean flatfish. The suffix is from the Latin forma meaning form, figure, or appearance.

  • Registration number. 962.

  • Reference phylogeny. A phylogeny inferred from sequences of 989 ultraconserved element (UCE) loci (Ghezelayagh et al. 2022, figs. S14–S15). Although Caranx hippos is not in the reference phylogeny, it resolves in a monophyletic Carangidae with other species of Caranx in phylogenies inferred from Sanger-sequenced genes and UCE loci (Reed et al. 2002, fig. 3; Damerau et al. 2018, fig. 1; Glass et al. 2023, fig. 2B). Phylogenetic relationships among the major lineages of Carangiformes are presented in Figure 17. The placement of the fossil pan-latid †Eolates in the phylogeny of Carangiformes is on the basis of phylogenetic analysis of morphological characters (Otero 2004).

  • Phylogenetics. The resolution of Carangiformes as a monophyletic group is one of several surprising results in the phylogenetics of Percomorpha to emerge over the past two decades (Miya et al. 2003, 2005; Betancur-R, Broughton, et al. 2013; Near et al. 2013; Musilova et al. 2019; Dornburg and Near 2021; Ghezelayagh et al. 2022). Carangiformes includes biologically and phenotypically disparate lineages, many of which have long evaded confident phylogenetic resolution. For example, Pleuronectoidei (flatfishes) are morphologically among the most atypical of all teleosts and prior to the application of molecular data had not been confidently placed among major lineages of percomorphs (Figure 1; Regan 1913b, 1929; Norman 1934; Chapleau 1993). On the other hand, the billfishes Istiophoridae (marlins) and Xiphias gladius (Swordfish) were classified with tunas in Scombroidei throughout the 20th century on the basis of presumably strong morphological evidence (Regan 1909b; Greenwood et al. 1966; Collette, Potthoff, et al. 1984; G. D. Johnson 1986; J. S. Nelson 2006:430–434), but are unvaryingly resolved within Carangiformes in molecular phylogenetic studies (e.g., Orrell et al. 2006; Little et al. 2010; Hughes et al. 2018; Ghezelayagh et al. 2022).

  • The lineages comprising Carangiformes were never grouped together in classifications based on morphology (Greenwood et al. 1966; Wiley and Johnson 2010); however, monophyly of the group is consistently supported in a wide range of molecular phylogenetic studies that include analyses of whole mtDNA genomes, Sanger-sequenced mtDNA and nuclear genes, and phylogenomic datasets (W.-J. Chen et al. 2003; Miya et al. 2003, 2005; Dettaï and Lecointre 2005, 2008; W. L. Smith and Wheeler 2006; W. L. Smith and Craig 2007; B. Li et al. 2009; C. H. Li et al. 2011; Betancur-R, Broughton, et al. 2013; Campbell, Chen, et al. 2013, 2014; Near et al. 2013; Davis et al. 2016; Harrington et al. 2016; Sanciangco et al. 2016; Smith et al. 2016; Betancur-R et al. 2017;Hughes et al. 2018; Ribeiro, Davis, et al. 2018; Shi et al. 2018; M. G. Girard et al. 2020; Ghezelayagh et al. 2022; M. G. Girard, Davis, Baldwin, et al. 2022; Mu et al. 2022). Phylogenetic analyses inferred from DNA sequences of more than 950 UCE loci and a combined dataset of 201 morphological characters and more than 450 UCE loci result in phylogenies that are strongly congruent and include three major clades within Carangiformes (M. G. Girard et al. 2020; Ghezelayagh et al. 2022): (1) Centropomus (snooks), Latidae (lates perches), Lactarius lactarius (False Trevally), and Sphyraena (barracudas); (2) Polynemidae (threadfins) and Pleuronectoidei (flatfishes); (3) and Carangoidei. The analysis of combined phenotypic and molecular characters results in the identification of morphological apomorphies for Carangiformes and several of the constituent lineages in the clade (M. G. Girard et al. 2020).

  • Composition. There are currently 1,107 living species of Carangiformes (Fricke et al. 2023) that include Lactarius lactarius, Mene maculata, Nematistius pectoralis, Xiphias gladius, and species classified in Centropomus, Leptobrama, Sphyraena, Istiophoridae, Latidae, Polynemidae, Carangoidei, and Pleuronectoidei (M. G. Girard et al. 2020; M. G. Girard, Davis, Tan, et al. 2022). Fossil lineages of Carangiformes include the pan-latid †Eolates gracilis (Sorbini 1970; Otero 2004) and several taxa in Carangoidei and Pleuronectoidei. Details of the ages and locations of the fossil taxa are presented in Appendix 1. Over the past 10 years, 36 new living species of Carangiformes have been described (Fricke et al. 2023), comprising 3.3% of the living species diversity in the clade.

  • Diagnostic apomorphies. Morphological apomorphies for Carangiformes include (1) presence of external process on the maxilla (M. G. Girard et al. 2020), (2) accessory gill rakers present on lateral aspect of branchial arches (M. G. Girard et al. 2020), (3) accessory gill rakers present on medial aspect of branchial arches (M. G. Girard et al. 2020), (4) presence of an epibranchial 2 toothplate that is serially associated with the second pharyngobranchial toothplate (M. G. Girard et al. 2020), (5) contact at metapterygoid-hyomandibular border ranging from a single pointed process inserting into evagination to a moderate amount of suturing between elements (M. G. Girard et al. 2020), (6) first hemal spine with a simple configuration, similar to more posterior hemal spines (M. G. Girard et al. 2020), and (7) pored lateral line scales absent from caudal fin (M. G. Girard et al. 2020).

  • Synonyms. Carangaria (Betancur-R et al. 2017:24), Carangimorphariae (Betancur-R, Broughton, et al. 2013, fig. 7; Betancur-R and Ortí 2014, fig. 1), and clade L (W.-J. Chen et al. 2003:279, tbl. 4; Dettaï and Lecointre 2005, fig. 3, tbl. 4, 2008, fig. 5, tbl. 4) are ambiguous synonyms of Carangiformes.

  • Comments. The resolution of the clade Carangiformes is not only one of several unexpected results in the molecular phylogenetics of Percomorpha (Dornburg and Near 2021), but also exemplifies the utility of molecular phylogenies in aiding with the discovery of morphological apomorphies for these newly delimited and inclusive lineages of teleost fishes (M. G. Girard et al. 2020). Over the past 10 years, the names Carangimorphariae (Betancur-R, Broughton, et al. 2013), Carangiformes (Davis et al. 2016, tbl. S3), and Carangaria (Betancur-R et al. 2017) have all been applied to this clade. We foll