Pseudomesochra T. Scott, 1902

Kim, Jong Guk, Lee, Jimin & Huys, Rony, 2021, New records of Pseudotachidiidae from South Korea, including a key to species of the Pseudomesochrinae (Copepoda: Harpacticoida), Zootaxa 5051 (1), pp. 387-422 : 403

Genus Pseudomesochra T. Scott, 1902

The genus—initially believed to be intermediate between Mesochra Boeck, 1865 (Canthocamptidae) and Cletodes Brady, 1872 (Cletodidae) —was established by Scott (1902: 461) to accommodate the type species P. longifurcata T. Scott, 1902 (by monotypy) from Loch Etive on the west coast of Scotland. Unaware of this description Sars (1906: 191) proposed the genus Stenheliopsis in the Diosaccidae (= Miraciidae ) for its type and only species S. divaricata Sars, 1906 from the south and west coasts of Norway, and subsequently added three new species, S. latifurca Sars, 1911 , S. media Sars, 1911 and S. affinis Sars, 1920 , all from southern Norway ( Sars 1911, 1920). Prior to these contributions Scott & Scott (1901: 343) had already described the morphologically similar species, Jonesiella brucei Scott & Scott, 1901 , from east of Hopen, Svalbard Archipelago. Brady (1880: 31) had placed Jonesiella Brady, 1880 (containing the species J. fusiformis Brady, 1880 and J. spinulosa Brady, 1880 ) in the subfamily Stenheliinae . Sars (1909: 328, 336) considered Jonesiella a junior subjective synonym of Danielssenia in the Tachidiidae , with J. brucei being treated as a valid member of this genus. Note that as a result of reconsidering the status of Danielssenia fusiformis ( Brady, 1880) nec Sars (1910) (the type species of Jonesiella ) Jonesiella has now been reinstated as a valid genus in the Danielsseniinae (then Paranannopidae ) ( Huys & Gee 1993: 62).

Monard (1927: 149, 159, 164) maintained Stenheliopsis in the Diosaccidae , placed Pseudomesochra in the Canthocamptidae , and considered both Jonesiella and Danielssenia as valid members (without listed species) of the Tachidiidae . In a later report ( Monard 1935: 16) it transpired that the author intended to restrict Jonesiella to include only J. brucei , a course of action that is in violation with the Code (ICZN Art. 67.2). Gurney (1932: 50) expressed the dissenting view that Pseudomesochra should probably be assigned to the Cletodidae . The author ( Gurney 1932: 49) also proposed the new replacement name Nannomesochra for the junior homonym Pseudomesochra Gurney, 1927 which was introduced for a new genus of Canthocamptidae ( Gurney 1927: 542) .

Having been associated with four different families Lang (1936b: 174; 1936c: 447–448) finally resolved the taxonomic mess surrounding Pseudomesochra by relegating Stenheliopsis to a junior subjective synonym of the latter and placing the genus in the Diosaccidae (= Miraciidae ), therefore endorsing Sars’s (1906: 192) earlier opinion that it is most closely related to Stenhelia Boeck, 1865 . He also considered Jonesiella brucei a valid species of Pseudomesochra .

The familial assignment of the genus remained unchallenged until Willen (1996) transferred it from the Miraciidae as the type of a new subfamily Pseudomesochrinae in the Paranannopidae . Huys et al. (1996: 236), building on the non-availability of the generic name Paranannopus Lang, 1936d [nomen nudum], introduced the new family name Danielsseniidae to replace Paranannopidae [nomen nudum], since family-group names taking their stem from an unavailable (and thus invalid) generic name, also become unavailable (ICZN Arts 11.7.1.1 and 63–64). The family Paranannopidae was relegated to a subfamily of the Pseudotachidiidae by Willen (1999); hence at this rank it should be cited as Danielsseniinae Huys and Gee in Huys et al. (1996) (cf. Huys 2009: 11). Willen (2000) maintained the Pseudomesochrinae as one of four subfamilies recognized in her new classification of the Pseudotachidiidae .A second genus, Keraia Willen & Dittmar, 2009 was added to the Pseudomesochrinae ( Willen & Dittmar 2009). The type genus Pseudomesochra has seen the addition of many new taxa since its proposal by Scott (1902) and currently includes 19 species ( Table 2). Both P. perplexa Bodin, 1968 and P. gemina Coull, 1973 have been regarded as species incertae sedis by some authors ( Willen 1996; Wells 2007) but are recognized as valid here.