Chaetopteridae forms a monophyletic clade showing an uncertain position within Annelida. The family has 75 ubiquitous species within four genera that cluster in two well-supported clades (Chaetopterus–Mesochaetopterus and Spiochaetopterus–Phyllochaetopterus) and includes several cryptic species complexes. Based on integrative taxonomy and supported by citizen science, here we describe one new and two unnamed species of Caribbean chaetopterids. Partial sequences from the nuclear 18S rRNA and mitochondrial Cytochrome Oxidase I genes of all known chaetopterid genera allowed us to (1) discuss the phylogeny of the family and (2) assign the three species into Mesochaetopterus (two) and Phyllochaetopterus (one). Mesochaetopterus stinapa, sp. nov. clearly diverged from all species of the genus, whereas Mesochaetopterus aff. xerecus forms a separate clade with Mesochaetopterus rogeri (Europe) and Mesochaetopterus xerecus (Brazil). Phyllochaetopterus aff. verrilli forms a separate clade with Phyllochaetopterus arabicus (Red Sea) and the closely related sequences from Hawai’i, Australia and French Polynesia attributed to Phyllochaetopterus verrilli (or cf. verrilli). Despite observing differences in morphology (e.g. palp colour pattern, presence or absence of eyespots, chaetal morphology and arrangement) and biogeographical distributions, only the erection of M. stinapa as a new species is well supported by the genetic distance, barcoding gap and species discrimination analyses. Our results emphasise the existence of cryptic species complexes within Mesochaetopterus and Phyllochaetopterus, whose taxonomy will require further morphological, biogeographical and molecular data to be resolved.

Some fossil Cantharidae from the Burmese amber have been reported, but it is still a poorly investigated group and some unknown taxa remain to be discovered. In this study, we employed comparative morphology and geometric morphometrics to uncover a new catharid genus from the mid-Cretaceous Burmese amber, and further investigate its phylogenetic position within Cantharidae by different cladistic methods. As a result, Brevipterus gen. nov., was defined to accommodate B. strungei (Fanti & Damggard, 2019) comb. nov. transferred from Sanaungulus and another three new species, B. acutiapicis sp. nov., B. abtusiapicis sp. nov. and B. megacephalus sp. nov., and the produced topologies indicate that the new genus is always grouped together with other members of the subfamily Cantharinae. These results will improve our knowledge about Burmite cantharids and provide some more early evidence in reconstructing the phylogeny of Cantharidae.

Marine worms of the genus Odontosyllis (Syllidae, Annelida) are well known for spectacular bioluminescent courtship rituals. During the reproductive period, the benthic marine worms leave the ocean floor and swim to the surface to spawn, using bioluminescent light for mate attraction. The behavioural aspects of the courtship ritual have been extensively investigated but little is known about the origin and evolution of light production in Odontosyllis that may be a key factor shaping the natural history of the group. To investigate the speciation patterns and evolutionary history of Odontosyllis, we inferred phylogenies following a gene concatenation approach using both maximum likelihood and Bayesian inference with a multilocus molecular dataset including nuclear (18S rRNA) and mitochondrial markers (16S rRNA and cytochrome c oxidase subunit I) from 51 Odontosyllis specimens. We also used the resulting phylogenetic tree to perform an ancestral state reconstruction analysis to trace the origin of bioluminescence within the group. Our results reveal that the genus Odontosyllis as currently delineated is a paraphyletic group that needs to be taxonomically revised to reflect evolutionary relationships. Nevertheless, our analyses recover two supported clades with bioluminescent species and suggest that the most recent common ancestor of luminous syllids was not bioluminescent, providing evidence that bioluminescence has evolved independently twice in the group. We discuss possible scenarios for the origin and evolution of light production and the potential role of bioluminescence courtship as a driver of speciation. Our results shed light on the evolutionary history of luminous syllids and suggest that bioluminescence might represent a key factor shaping the evolution of these organisms.

Theromyzon Philippi, 1867 is a genus of sanguivorous, freshwater leeches in the family Glossiphoniidae. The genus is broadly distributed across the globe, possibly due to the frequent feeding in the nasopharyngeal cavities of migratory waterfowl that may allow for long distance dispersal. The genus has a history of taxonomic confusion resulting from mischaracterisations of key morphological features of type specimens that have produced several re-descriptions and synonyms. Here, we bring partial order to this confusion through robust morphological investigations of newly collected North American (and a single South American) specimens, representing most of the known species diversity from this continent. We also produce the first species-level phylogeny for Theromyzon and attempt to understand species boundaries regarding both morphology and genetics. Our results demonstrate that there are at least five species of Theromyzon present in North America (T. bifarium, T. tessulatum, T. rude, T. trizonare, and a clade that needs further investigation), and a hitherto undescribed taxon that does not conform to any previously published description, and represents a unique lineage in the phylogeny; we describe this new species under the name Theromyzon tigris sp. nov. This study sheds light on the discriminatory power of select morphological characters and the distribution of phenotypes within the genus. We also provide a comprehensive classification framework for the known species within the genus designed to facilitate identification and minimise future taxonomic confusion.

The spider genus Metagonia has been represented on the Galápagos Islands by two blind species inhabiting lava tubes on Isabela and Santa Cruz. Epigean relatives had not been found on Galápagos and were thus thought to be extinct. During a collecting trip in 2019 we found two epigean species and a third blind hypogean species. Here we describe these new species based on males and females, redescribe both previously known species, and add all five species to the recently published molecular phylogeny of Pholcidae, together with more than 30 further congeners from the mainland. Galápagos Metagonia is recovered as a monophyletic group within the South American–Caribbean M. potiguar group. Galápagos Metagonia is divided into an epigean clade and a hypogean clade. Each species is restricted to an individual island (Isabela or Santa Cruz; with one possible exception), suggesting that the epigean Metagonia species are native rather than introduced.

ZooBank registration: http://zoobank.org/References/0812B715-8446-4B28-BCE0-6AB504BBEC7E.