Mussel of the Month

Pseudunio homsensis is a worthy Mussel of the Month for a couple reasons. Back in January, we discussed the recent revisions of the Margaritiferidae that resulted in Margaritifera sensu lato being split into four genera: Margaritifera s.s., Gibbosula, Cumberlandia, and Pseudunio (Lopes-Lima et al., 2018). The "old sense" of the Recent Margaritiferidae being composed of a single genus (i.e., Margaritifera) is actually relatively new. Smith (2001) called this mussel Pseudunio homsensis and split Margaritifera s.l. among three genera. These oscillations in genus richness demonstrate that the taxonomy is still unsettled.

Like most of the species of Gibbosula, P. homsensis had been classified in the Unionidae. In fact, the prevailing view seemed to be that this taxon was merely a subspecies: Potomida littoralis homsensis (Haas, 1940, 1969; Schütt, 1983). However, the presence of mantle-attachment scars provided morphological evidence to confirm its classification in the Margaritiferidae (Falkner, 1994; Smith, 2001).

One of the major challenges of keeping track of freshwater mussel taxonomy is its complex history. The International Code of Zoological Nomenclature and the Principle of Priority (among others) necessitates a method for documenting historical precedence. The MUSSEL Project Database on this web site is just the sort of tool for tracking this information. On this very page, there are links to the specimen in the figure above, to the nomimal species Margaritana syriaca (a junior synonym of P. homsensis), the species Pseudunio homsensis, and the genus Pseudunio. From those links, it is easy to browse or search for more information in the database.

For example, for any nominal species (like Margaritana syriaca), the MUSSELpdb provides infromation about where it was described, the valid species to which it is assigned, an image of the type (if available), and a history of name use in various publications.