The genus-group name Propappus Seeley, 1888 was established for a Permian pareiasaurian reptile, Propappus omocratus Seeley, 1888, collected at Brak River, Fort Beaufort, South Africa. According to Watson (1914), the holotype specimen of this pareiasaur in the Natural History Museum in London (BMNH R4064; A.G. Bain collection) consists of a sacrum, an os innominatum, a femur, a tibia, a part of a humerus, and caudal vertebrae. However, the original description, given in a brief abstract (Seeley, 1888), was based on a single fossilized bone (from the above-mentioned specimen), first mistaken by the author for a humerus but later re-interpreted as a femur (Seeley, 1892, figs. 10–11; Broom, 1908). Seeley's main reason for establishing a new genus was that he considered the bone to indicate an intermediate stage between reptiles and early mammals. Lee (1997), who reviewed this case in detail, noted that Seeley had intended to write a full paper on his new taxon but soon realized that he had been on the wrong track. Seeley (1892: 354) suggested that Propappus was a junior synonym of Pareiasaurus Owen, 1876, yet he retained the name Propappus, by suggesting that “until other parts of the skeleton justify the revival of the name Propappus, that type may be referred to as Pareiasaurus (Propappus) minor”; although the impression of subgeneric rank for Propappus was possibly unintentional. His new nominal species Pareiasaurus (Propappus) minor was thus an objective junior synonym of Propappus omocratus. Lee (1997: 268) commented, “This (illegitimate) change was proposed in a brief sentence buried in the detailed description of ‘Pareiasaurus baini’ and has either been overlooked or disregarded by most subsequent workers.” Also, to be noted is that Seeley himself (1891: 519), while discussing the characters that distinguish Anthodon Owen, 1876 from Pareiasaurus, had earlier stated “that the genus Propappus apparently has no existence, being founded on a femur.” Despite all this, two additional taxa of fossil reptiles were subsequently described by other authors as separate species of Propappus, Pr. rogersi Broom, 1912 and Pr. parvus Haughton, 1913.
Lee (1997: 233) summed up most 20th-century authors' work on pareiasaurs by stating, “The plethora of invalid names and constant, illegitimate reshuffling of taxa has caused the existing literature on pareiasaurs to be almost impenetrable to the uninitiated.” During the 1900s, Propappus Seeley, 1888 was mentioned repeatedly in the paleontological literature but over the years was increasingly regarded as a junior synonym of Pareiasaurus Owen, 1876. Some of the earlier authors (e.g., Broom, 1908, 1912; Haughton, 1913; Watson, 1914) evidently regarded Propappus as valid (see para. 1 above), although Broom (1936), in a late phase of his career, was prepared to synonymize Seeley's Pr. omocratus with Owen's Pareiasaurus serridens (see Findlay, 1970). Early revisions of pareiasaurian taxonomy (Haughton & Boonstra, 1929; Boonstra, 1934) retained the genus Propappus, and as late as 1963, Young & Yeh (1963: 212) did “not think it is all right to consider the genus Propappus as a synonym of Pareiasaurus”, but their discussion dealt only with Propappus rogersi, without mentioning the type species Propappus omocratus. The comparison by Young & Yeh (1963) of a Chinese fossil with Propappus and other South African pareiasaurian genera was referred to by Benton (2016), but without any further comment. In more recent taxonomic revisions of pareiasaurs, Propappus came to be explicitly regarded as a junior synonym of Pareiasaurus (Kuhn, 1969; Kitching, 1977; Ivakhnenko, 1987; Lee, 1997). Lee (1997: 265, table 1) regarded Propappus omocratus, Pareiasaurus (Propappus) minor and Propappus rogersi as junior synonyms of the type species of Pareiasaurus (Pa. serridens Owen, 1876), whereas Kuhn (1969) and Ivakhnenko (1987) regarded Pa. omocratus as a species separate from Pa. serridens. Propappus parvus was regarded as a distinct species of Pareiasaurus by Kuhn (1969) and Ivakhnenko (1987), as a junior synonym of Pa. serridens by Kitching (1977) and as a junior synonym to Anthodon serrarius Owen, 1876 by Lee (1997). In short, pareiasaurian taxonomy has been in a state of confusion and instability for at least a century, but now it seems that Propappus Seeley, 1888 finally has become a redundant name, returning to the status given it by the original author about 130 years ago (Seeley, 1891; see para. 1).
The genus-group name Propappus Michaelsen, 1905 (for a genus of Eurasian worms in Annelida, Clitellata/Oligochaeta), with Propappus glandulosus Michaelsen, 1905 as the type species, is a junior homonym of Propappus Seeley, 1888. Propappus Michaelsen and the more recently established family name Propappidae Coates, 1986 have both been in continuous use in the taxonomic literature of Clitellata (or Oligochaeta) up until the present day. We have recognized about 200 scientific publications (mostly journal articles, some textbooks) dealing with Propappus in one way or another. Over 80 different first authors are involved, and in the Appendix we list 50 references as representative examples of the wealth of such studies during a period of more than 100 years.
Michaelsen (1916) described a second species of Propappus, P. volki Michaelsen, 1916, which subsequently has been recorded from several parts of Eurasia and possibly also from Canada (see Torii, 2006: 359). Most of the literature on Michaelsen's Propappus quoted above deals with this taxon, and there is molecular evidence that it refers to a species complex rather than a single panmictic metapopulation (Erséus et al., unpublished data). Michaelsen (1916: 52) mentioned that earlier in 1916 he had reported this taxon as a member of another (and new) genus: “Palpenchytraeus volki, n. gen., n. sp.” He was referring to a brief report of the annual meeting of the “Naturwissenschaftlicher Verein zu Hamburg” held on 26 January 1916, which was published in a newspaper (“Hamburger Nachrichten”; Anonymous, 1916) on 30 January 1916. Unfortunately, the exact publication date of Michaelsen's description of Propappus volki is unknown. His paper was included in a volume that served as the annual report of Naturwissenschaftlicher Verein zu Hamburg for 1915, published in 1916, and the conclusion must be that it was distributed after 30 January. By courtesy of the State Archives of Belgium, we obtained a copy of the newspaper report (Anonymous, 1916), which gives a brief account of Michaelsen's presentation of the new taxon named Palpenchytraeus volki, describing it as a “winzig kleinen Wurm, dessen Kopflappen zum Unterschiede von seinen Verwandten zu einem Rüssel ausgebildet ist” [our translation: tiny little worm that, unlike its relatives, has its head lobe formed into a trunk]. Although Michaelsen (1916) had changed his mind about using the name Palpenchytraeus volki when he gave his more comprehensive description of Propappus volki, we find the former to be an available name in the meaning of the Code. Under Article 8.1 of the Code, the publication establishing the name “must be obtainable, when first issued, free of charge or by purchase”, and “in an edition containing simultaneously obtainable copies by a method that assures numerous identical and durable copies”. Moreover, the description of Palpenchytraeus volki complies with Art. 12.1, requiring the name to “be accompanied by a description or a definition of the taxon that it denotes”. In this case, the newspaper report was not signed, but Art. 50.2 states that “if the name of a taxon is made available by publication in a report or minutes of a meeting, the person responsible for the name, not the Secretary or other reporter of the meeting, is the author of the name”. Regardless of all this, we have only found two works mentioning the name Palpenchytraeus in the taxonomic literature after 1916. Welch (1920) merely reiterated Michaelsen's (1916) own account concerning this name, while Coates (1986) regarded Palpenchytraeus volki as a nomen nudum, assuming that it lacked a formal description (Coates, pers. comm.).
We thus conclude that Palpenchytraeus Michaelsen, 1916 is a junior synonym of Propappus Michaelsen, 1905, and therefore eligible to be proposed as a replacement name for the junior homonymy Propappus Michaelsen, 1905. We argue, however, that if this name is adopted, its etymology, which suggests an affinity to Enchytraeus and Enchytraeidae (Propappidae would be replaced by “Palpenchytraeidae” [see para. 9 below]) may unnecessarily add to confusion surrounding the taxonomy of these taxa.
Propappus Michaelsen has a unique position within Clitellata, although it comprises a mere handful of known species. It was originally included in the family Enchytraeidae, but on morphological grounds Coates (1986) elevated its status, making it the type genus of a separate family within Clitellata, Propappidae Coates, 1986. This separation from Enchytraeidae has been reinforced by recent ultrastructural and molecular studies, but while the evidence from a genome-level analysis of transcriptomic data supports a sister-group relationship between Propappidae and Enchytraeidae (Erséus et al., 2020), the exact systematic position of Propappidae among other clitellates is less resolved in other phylogenetic studies (Gustavsson et al., 2008; Marotta et al., 2008; Gorgoń et al., 2015). Thus, the systematics of Propappidae as a worm family is highly relevant to more general questions of clitellate evolutionary history.
We argue that maintaining the precedence of the senior homonym of Propappus would serve no purpose for stability in the taxonomy of pareiasaurian reptiles. Given the taxonomic history of Propappus Seeley, 1888, the probability that this name might be subsequently revalidated in pareiasaur taxonomy is low. As was noted in para. 1 above, even the original author soon realized that the name was redundant (Seeley, 1891, 1892). Moreover, applying the Principle of Priority would cause confusion and instability in the well-established taxonomy associated with the junior homonym, the worm genus Propappus Michaelsen, 1905. This name is in wide use and the genus is unambiguously defined, not being associated with issues of synonymy or splitting/lumping other than those possibly engendered by cryptic speciation (Erséus et al., unpublished work in progress). Moreover, both this genus and the family-group name Propappidae are today well-established in the classificatory infrastructure of Clitellata (or Oligochaeta), e.g., in web-based databases, such as WoRMS, GBIF, Encyclopedia of Life, Catalogue of Life and Wikipedia.
For reversal of precedence without an appeal to the International Commission on Zoological Nomenclature, two conditions must be fulfilled according to Art. 23.9. First, the senior homonym must not have been used as a valid name after 1899 (Art. 184.108.40.206), and second, the junior homonym must have been used for a particular taxon, as its presumed valid name, in at least 25 works, published by at least 10 authors in the immediately preceding 50 years and encompassing a span of no less than 10 years. In the present case, the second condition applies to the junior homonym (para. 3). However, the senior homonym has been regarded as valid after 1899 (e.g., Propappus rogersi and Pr. parvus were both described after 1899; see para. 1). Thus, the conditions for reversal of precedence stipulated by Art. 220.127.116.11 are only partly fulfilled.
Conservation of Propappus Michaelsen, 1905 is clearly desirable, also with respect to the family-group name based on it. The long-term prevailing usage of both names suggests that complete suppression of the senior homonym Propappus Seeley, 1888 is both desirable and necessary.
The International Commission on Zoological Nomenclature is accordingly asked:
(1) to use its plenary power to rule that the generic name Propappus Seeley, 1888 be suppressed for the purposes of both the Principle of Priority and the Principle of Homonymy;
(2) to place on the Official List of Generic Names in Zoology the name Propappus Michaelsen, 1905 (gender: masculine), type species: Propappus glandulosus by original designation by Michaelsen, 1905 (Annelida, Clitellata); and
(3) to place on the Official Index of Rejected and Invalid Generic Names in Zoology the name Propappus Seeley, 1888 (Vertebrata, Reptilia), as suppressed in (1) above.
We thank Marc Van den Brandt, University of the Witwatersrand, Johannesburg, South Africa, for invaluable input about the history of Propappus Seeley; Kathryn A. Coates, Research Associate of the Department of Natural History, Royal Ontario Museum, Toronto, Canada, for informal information on her previous research; Pierre-Alain Tallier and Els Herrebout at State Archives of Belgium, for obtaining an old copy of “Hamburger Nachrichten”; and Thomas Pape, Natural History Museum of Denmark, for advice and constructive criticism on an early version of the manuscript.
The following references are significant evidence of the prevailing usage of Propappus Michaelsen. The papers span a period of over a century, from 1916 to the present day. Most publications are articles in scientific journals whereas those with an asterisk (*) are identification keys and those with two asterisks (**) are textbooks or large monographs.
Baturina M (2007) Oligochaeta of the Pechora River Basin, Russia. Acta Hydrobiologica Sinica 31 (suppl.): 36–46.
Baturina M (2012) Distribution and diversity of Oligochaeta in small streams of the middle taiga. Turkish Journal of Zoology 36: 75–84.
Behning A (1924) Einige Ergebnisse qualitativer und quantitativer Untersuchungen der Bodenfauna der Wolga. Internationale Vereinigung für Theoretische und Angewandte Limnologie: Verhandlungen 2 (1): 71–94.
Behning A (1926) Das Leben der Wolga. Nach dem am 31. August in Saratow gehaltenen Vortrag. Internationale Vereinigung für Theoretische und Angewandte Limnologie: Verhandlungen 3 (1-2): 157–164.
Berg LS (1934) O пpeдпoлaгaeмыx мopcкиx элeмeнтax в фayнe и флope Бaйкaлa. [About the alleged marine elements in the fauna and flora of Lake Baikal] Bulletin de l'Académie des Sciences de l'URSS 2-3: 303–326. [In Russian]
Bird GJ (1982) Distribution, life cycle and population dynamics of the aquatic enchytraeid Propappus volki (Oligochaeta) in an English chalkstream. Holarctic Ecology 5 (1): 67–75.
*Brinkhurst RO (1971) A guide for the identification of British aquatic Oligochaeta. Kendal, Wilson, 53 pp.
Brinkhurst RO (1992) Evolutionary relationships within the Clitellata. Soil Biology and Biochemistry 24 (12): 1201–1205.
**Brinkhurst RO, Jamieson BGM (1971) Aquatic Oligochaeta of the world. Oliver and Boyd, Edinburgh, 860 pp.
Caramelo C, Martinez-Ansemil E (2010) External sense receptors in microdrile oligochaetes (Annelida, Clitellata) as revealed by scanning electron microscopy: Typology and patterns of distribution in the main taxonomic groups. Journal of Morphology 271 (12): 1482–1492.
Cellot B, Juget J (1998) Oligochaete drift in a large river (French Upper Rhône): the effect of life cycle and discharge. Hydrobiologia 389: 183–191.
**Chekanovskaya OV (1981) Aquatic Oligochaeta of the USSR. Amerind Publishing Co. Pvt. Ltd., New Delhi, 513 pp.
Coates KA (1986) Redescription of the oligochaete genus Propappus, and diagnosis of the new family Propappidae (Annelida: Oligochaeta). Proceedings of the Biological Society of Washington 99 (3): 417–428.
Dumnicka E (1994) Communities of oligochaetes in mountain streams of Poland. Hydrobiologia 278: 107–110.
Dumnicka E (2006) Composition and abundance of oligochaetes (Annelida: Oligochaeta) in springs of Kraków-Częstochowa upland (Southern Poland): Effect of spring encasing and environmental factors. Polish Journal of Ecology 54 (2): 231–242.
Dumnicka E, Wojtan K (1989) L'influence du milieu et des paramètres physico-chimiques de l'eau sur les peuplements des Oligochètes et la variabilité des populations de Propappus volki (Enchytraeidae) dans la grotte Wodna (Tatras Montagnes, Pologne) Mémoires de Biospéologie, 16: 225–232.
Erséus C, Källersjö M (2004) 18S rDNA phylogeny of Clitellata (Annelida). Zoologica Scripta 33 (2): 187–196.
Erséus C, Rota E, Timm T, Grimm R, Healy B, Lundberg S (2005) Riverine and riparian clitellates of three drainages in southern Sweden. Annales de Limnologie 41 (3): 183–194.
Erséus C, Williams BW, Horn KM, Halanych KM, Santos SR, James SW, Châtelliers MC, Anderson FE (2020) Phylogenomic analyses reveal a Paleozoic radiation and support a freshwater origin for clitellate annelids. Zoologica Scripta 49: 614–640. doi: 10.1111/zsc.12426.
Fomenko NV (1980) Ecological groups of Oligochaeta worms in the Dnieper Basin. Aquatic Oligochaeta Worms. Amerind Publishing Co. Pvt. Ltd., New Delhi, pp. 105–118.
Gerd SV (1950) Oлигoxeты вoдoeмoв Кapeлии. [Aquatic Oligochata from Karelia] Извecтия Кapeлo-Финcкoгo филиaлa Aкaдeмии нayк CCCP [Notices from the Karel-Finnish Branch of the Academy of Sciences of the USSR] 1: 56–71. [In Russian.]
Gorgoń S, Krodkiewska M, Świątek P (2015) Ovary ultrastructure and oogenesis in Propappus volki Michaelsen, 1916 (Annelida: Clitellata). Zoologischer Anzeiger 257: 110–118.
Gustavsson LM, Ferraguti M, Marotta R (2008) Comparative ultrastructural study of the cuticle and spermatozoa in Propappus volki Michaelsen, 1916 (Annelida: Clitellata). Zoologischer Anzeiger 247 (2): 123–132.
Horn KM, Williams BW, Erséus C, Halanych KM, Santos SR, Creuze des Chatelliers M, Anderson FE (2019) Na(+) /K(+) -ATPase gene duplications in clitellate annelids are associated with freshwater colonization. Journal of Evolutionary Biology 32 (6): 580–591.
Ladle M (1971) Studies on the biology of oligochaetes from the phreatic water of an exposed gravel bed. International Journal of Speleology 3 (3/4): 311–316.
Lafont M, Durbec A, Ille C (1992) Oligochaete worms as biological describers of the interactions between surface and groundwaters: A first synthesis. Regulated Rivers: Research & Management 7 (1): 65–73.
Lafont M, Malard F (2001) Oligochaete communities in the hyporheic zone of a glacial river, the Roseg River, Switzerland. Hydrobiologia 463 (1/3): 75–81.
Lastochkin DA (1935) LXV.— Two new river Æolosomatidæ (Oligochæta limicola). Annals and Magazine of Natural History (series 10) 15: 636–645.
Marotta R, Ferraguti M, Erséus C, Gustavsson LM (2008) Combined-data phylogenetics and character evolution of Clitellata (Annelida) using 18S rDNA and morphology. Zoological Journal of the Linnean Society 154 (1): 1–26.
Martin P, De Broyer C, Fiers F, Michel G, Sablon R, Wouters K (2009) Biodiversity of Belgian groundwater fauna in relation to environmental conditions. Freshwater Biology 54 (4): 814–829.
Michaelsen W (1916) Ein eigentümlicher neuer Enchyträide der Gattung Propappus aus der Niederelbe. Verhandlungen des Naturwissenschaftlichen Vereins zu Hamburg 23: 51–55.
Michaelsen W, Vereščagin G (1930) Oligochaeten aus dem Selenga-Gebiete des Baikalsees. Travaux de la Commission pour l'étude du lac Bajkal 3: 213–226.
Omodeo P (1998) History of Clitellata. Italian Journal of Zoology 65 (1): 51–73.
Römbke J, Schmidt M (1990) Setal morphology of some species of terrestrial Enchytraeidae (Oligochaeta). Transactions of the American Microscopical Society 109 (1): 44–51.
**Semernoy VP (2004) Oligochaeta of Lake Baikal. Nauka, Novosibirsk, 527 pp.
Sokolskaya NL (1983) Freshwater Oligochaeta of Kamchatka and the Koryak upland. Sbornik Trudov Zoologicheskogo Muzeya MGU 20: 22–119. [In Russian]
Särkkä J, Mäkelä J (1999) Meiofauna of esker groundwaters in Finland. Hydrobiologia 405: 25–37.
Taş M, Elipek BÇ, Kırgız T, Arslan N, Yıldız S (2012) The aquatic and semi-aquatic Oligochaeta fauna of Turkish Thrace. Journal of FisheriesSciences.com 6 (1): 26–31.
Timm T (1970) On the fauna of the Estonian Oligochaeta. Pedobiologia 10: 52–78.
Timm T (1994) Propappidae and aquatic Enchytraeidae (Oligochaeta) from the farthest southeast of Russia. Hydrobiologia 278 (1-3): 67–78.
Timm T (1997) Freshwater Oligochaeta of some urban watercourses in the Russian Far East. Internationale Revue der Gesamten Hydrobiologie und Hydrographie 84 (4): 437–467.
Timm T (1999) Oligochaeta of the Edinka Stream, Russian Far East. Species Diversity 4: 1–7.
*Timm T (2009) A guide to the freshwater Oligochaeta and Polychaeta of Northern and Central Europe. Lauterbornia 66: 1–235.
Timm T (2012) Life forms in Oligochaeta: a literature review. Zoology in the Middle East 58 (supplement 4): 71–82.
*Timm T, Martin P (2019) Phylum Annelida: Class Clitellata: Subclass Oligochaeta. Thorp and Covich's Freshwater Invertebrates: Volume 4: Keys to Palaearctic Fauna. Elsevier, London, pp. 364–483.
Timm T, Vvedenskaya TL (2006) Oligochaeta (Annelida) of Lake Kurilskoe, Kamchatka Peninsula. Species Diversity 11: 225–244.
Torii T (2006) New Record of Propappus volki (Annelida: Clitellata: Propappidae) from Japan. Species Diversity 11 (4): 359–365.
*van Haaren T, Soors J (2013) Aquatic Oligochaeta of the Netherlands and Belgium. KNNV Publishing, Zeist, 304 pp.
Welch PS (1920) The genera of the Enchytraeidae (Oligochaeta). Transactions of the American Microscopical Society 39 (1): 25–50.
Verdonschot PFM (2006) Beyond masses and blooms: the indicative value of oligochaetes. Hydrobiologia 564 (1): 127–142.
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