Revalidation of the genus Thoracophelia Ehlers, 1897, replacing Euzonus Grube, 1866 (Polychaeta: Opheliidae), junior homonym of Euzonus Menge, 1854 (Arthropoda: Diplopoda), together with a literature summary and updated listing of Thoracophelia species

Brewer et al. (2011) recently demonstrated that the generic name Euzonus was being used in both Arthropoda (Diplopoda) and Polychaeta (Opheliidae) systematics and that the arthropod name was the senior synonym. The diplopod name Euzonus Menge, 1854, based on a single species, E. collulum Menge, 1854 from Baltic amber predates Euzonus Grube, 1866, established for E. arcticus Grube, 1866 from the Arctic Ocean. The Nomenclator Zoologicus (2005) verifies that both names are listed as uncorrected homonyms. Brewer et al. (2011) suggested that for time being, the genus Pectinophelia Hartman, 1938 could be used for those species of Polychaeta currently referred to the genus Euzonus. However, prior to Hartman’s (1956) referral of these opheliids to the genus Euzonus, some species had been included in the genus Thoracophelia Ehlers, 1897 and this is clearly the next available name for polychaetes currently referred to Euzonus Grube. In the following paragraphs I summarize some key decision points in the taxonomic history of these opheliids, their referral to Thoracophelia, and why subgenera, as currently applied, are not necessary. The polychaetes that have been referred to Euzonus are unusual among the Opheliidae in having the body divided into three distinct regions: (1) an anterior cephalic region formed of the prostomium and first two setigers; (2) a swollen thoracic region, usually through setigers 2–10; and (3) a long narrow posterior region with a distinct ventral groove; sometimes the posterior pygidial region is enlarged or modified. Branchiae are limited to the posterior region, but are typically absent from the posteriormost segments. Santos et al. (2004) also noted that all species of these opheliids have a lateral modification of setiger 10, either as a flap arising from the body wall or with rows or patches of papillae. Two species referred to the genus Lobochesis Hutchings & Murray, 1984 also share these characters and were referred to Euzonus by Santos et al. (2004). This synonymy was further supported as part of a cladistic analysis of opheliids by Sene Silva (2007) who demonstrated that the two species of Lobochesis were nested within a monophyletic clade of Euzonus species. The current arrangement of species and subgenera of the opheliids referred to Euzonus Grube date from Hartman (1938, 1944, 1956, 1959, and 1969). At time of Hartman’s 1938 publication, these polychaetes were included in Thoracophelia Ehlers with four known species: T. furcifera Ehlers, 1897, T. mucronata (Treadwell, 1914), T. ezoensis Okuda, 1934, and T. yasudai Okuda, 1936. Euzonus arcticus Grube had not yet been recognized as belonging to this group of species, despite redescriptions and records of the species by Augener (1912) and Annenkova (1935). Hartman (1938) described two new species that had distinct pinnules arising from the branchiae and established a new genus, Pectinophelia, to accommodate them (P. dillonensis Hartman, 1938 and P. williamsi Hartman, 1938). She also referred both of Okuda’s species to this new genus, leaving T. furcifera and T. mucronata, both with simple branchiae, in Thoracophelia. The generic separation among these six species was, therefore, based on the presence or absence of pinnules on the branchiae. Hartman (1944) retained this classification but extended the range of T. mucronata from southern California, where it had originally been reported, to British Columbia where it had been found by Berkeley & Berkeley (1932). Hartman (1944) also reported T. mucronata from Dillon Beach, California, where both Pectinophelia dillonensis and P. williamsi were originally described. This was the first time that all three California species were noted to occur in the same area, sometimes in the same samples. Hartman (1956) recognized Euzonus Grube, 1866, for the first time and referred all species of Thoracophelia and Pectinophelia to this genus. She retained the earlier branchial distinction through the use of two subgenera: Euzonus (Thoracophelia) for species having simple branchiae and Euzonus (Euzonus) for species having branchiae with pinnules.