This month, we’ll review the recent taxonomic turmoil associated with this species, and then point out how the MUSSEL Project Web Site has useful resources to deal with (and discover!) classification conundra.
Simpsonasus is a new genus name for an old species — about which few have any modern knowledge. Until recently, Simpsonasus nankingensis was regarded as two separate species classified as Pseudodon in our most recent published checklist: P. nankingensis and P. secundus (Graf & Cummings, 2021). Those names had been in use since 1877, but most sources only mentioned them to say that they were thought to exist. Every new checklist of freshwater mussel species and genera noticed the work of previous checklists. Existence was the extent of the knowledge. It is for solving just this sort of taxonomic riddle that the MUSSELp Web Site (http://mussel-project.net) was created.
In 2023, Bolotov et al. produced a revised revision of the Pseudodontini, the tribe for which the genus Pseudodon is the type. That work was a detailed study of the pseudodontine species and genera for which there are genetic data sufficient for phylogenetic analysis. That almost always means access to freshly collected material from which DNA can be extracted. As we recently reviewed in October 2023 when Thaiconcha callifera was Mussel of the Month, the Pseudodontini has been taxonomically stretched and pulled to recognize a richness of taxa unknown a decade ago. Bolotov et al. (2023) had no new data on the status of “Pseudodon” nankingensis, but they were able to apply some useful logic to improve the taxonomic situation.
Even without any COI or 28S nucleotides to analytically test the traditional classification of “Pseudodon” nankingensis, a detailed reappraisal of the genus Pseudodon is sufficient to show that our Mussel of the Month doesn’t belong. “Pseudodon” nankingensis — if that is its real name — would be the only Pseudodon from the Yangtze-Huang subregion; in fact, it would be the only pseudodontine. That biogeographic zone is more typical of the Gonideini (same subfamily, different tribe), a family-group more fitting for a mussel with a shell like “Pseudodon” nangkinensis. See Ptychorhynchus pfisteri (Gonideini) for comparison.
Actually, “Pseudodon” nankingensis wouldn’t have been the only Pseudodon from that part of the world: “Pseudodon” secundus was another little-known species from the same area. The classification of these nominal species was messing up a tidy Pseudodon restricted to the Indochina, Sunda-Philippines, and India-Myanmar subregions.
Fortunately, “Pseudodon” nankingensis is the type species for the genus-group name, Nasus Simpson, 1900. It would be so simple just call it “Nasus” nankingensis, classify Nasus in the Gonideini, sink “Pseudodon” secundus as a junior synonym, and be done with. That is basically what Bolotov et al. (2023) did, except that the name Nasus Simpson, 1900 is preoccupied by the senior homonym Nasus Basilewski, 1855 (Actinopterygii: Cyrinidae). Thus, a replacement genus name was required, and Simponasus nankingensis received its current combination.
Of course, the MUSSEL Project Database — served on the MUSSEL Project Web Site — has been updated to reflect these taxonomic changes. Simpsonasus nankingensis is Simpsonasus nankingensis. But, it is worth exploring where and how these types of data can be found since these are just the sorts of puzzles systematists need the resources to solve.
For each biogeographic region — e.g., East Asia — there is a summary page listing all of the species reported to occur there: https://mussel-project.uwsp.edu/fmuotwaolcb/east_asia.html.
Those data are useful for finding biogeographical outliers.
For each valid species, like Simpsonasus nankingensis, there is a page that reports the specimens we have in our database: https://mussel-project.uwsp.edu/fmuotwaolcb/validsp_1151.html. The georeferenced localities of those voucher records are used to produce a map, and the recent history of taxonomic combinations is provided.
A more comprehensive summary of species taxonomy can be found in the nominal species page that lists the published synonyms: https://mussel-project.uwsp.edu/fmuotwaolcb/validsp_1151_syn.html. For each available name (as well as literature misidentifications and other errors), a wealth of pertinent data are provided: the original combination, a citation, a primary type specimen, images, and a taxonomic history of every combination (that we know of) to which the nominal species as been assigned, as a valid name or synonym.
The MUSSEL Project Web Site (http://mussel-project.net) is a one-stop clearinghouse of data about the taxonomy of Simpsonasus nankingensis and all other species, genera, and families of Recent freshwater mussels. For other such taxa that have been better studied, there is even more information. Click around and find out!
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