Mussel of the

Page last updated
24 March 2020

Mussel of the Month

The 2020 Mussels of the Month, so far ...

April 2020

PisidiumPisidium amnicum (Sphaeriidae, Widespread)

The April 2020 Mussel of the Month is Pisidium amnicum. Pisidium is a globally distributed freshwater bivalve genus of more than 50 valid species.

This isn’t the first time that we have chosen a non-mussel as the freshwater mussel of the month. As recently as last February, we selected Monodacna colorata for Valentines Day, and for April Fools 2013, it was Corbicula fluminea. The selection of a sphaeriid clam (= fingernail or pea clam) this month is to highlight (once again) how much information we have on this site about freshwater bivalves generally —although our bias admittedly leans heavily toward the Unionoida.

This month, we want to call attention to a bit of data entry we have recently completed. Thanks to the generosity of our friend, Yuri Kantor, we have recently captured the bivalve data in Vinarski & Kantor (2016). That means, we have captured their combinations of genera and species, and those data are served in the Mussel Project Database. This includes freshwater mussels, the Sphaeriidae, and the other freshwater bivalve taxa found in the former Soviet Union. We have written quite a bit about Russian bivalve taxonomy over the years, most recently in the context of Anodonta anatina.

In the MUSSELpdb, you can access those taxonomic opinions at the level individual species. For example, in the synonym of Pisidium amnicum, at the very top is Tellina amnica Müller, 1774. That is the original combination of the nominal species. Our data suggest that the species has been regarded as valid since it was described (true for the minority of freshwater bivalves). Each of those opinions comes with a link to relevant references — e.g., Vinarski & Kantor (2016).

If you click the link to that publication (or any publication), you can get a list of genera and/or species introduced therein, as well as a list of species regarded as valid and their synonyms.

As of the instant of typing this sentence, we have 76084 taxonomic opinions about species from 1400 different works. Some entries are more complete that others, but we hope that these data provide an entree to the freshwater bivalve literature.

March 2020

IndonaiaIndonaia caerulea (Unionidae, East Asia)

The March 2020 Mussel of the Month is Indonaia caerulea. Indonaia is a genus of 14 species found from India east to Thailand.

Back in 2007, when we published our first global checklist of freshwater mussels (Graf & Cummings, 2007), we didn’t treat the genus name Indonaia as valid. Instead, we followed the going taxonomy of Subba Rao (1989), Ramakrishna & Dey (2007) and others to lump those species under Parreysia (Radiatula). Then (as now) we were not fans of subgenera, but the concept of the genus Parreysia at the time was unwieldy, and we made an exception to acknowledge that other contemporary classifications recognized Radiatula as a distinct genus (e.g., Nesemann et al., 2007). Nowadays, with the availability of molecular phylogenies, the tendency has been to recognize the few species of Indonaia that have been analyzed as a clade distinct from the rest of Radiatula (Bolotov et al., 2017; Konopleva et al., 2019). And so, here we are with Inodonaia caerulea, the type species of the genus.

Among the difficulties of studying freshwater mussel systematics is making sense of the history of name changes and re-classifications over the decades and centuries. The rules of the ICZN require us to care about priority and first revisers, and as such the past is our business. Fortunately, the MUSSEL Project Database is available to assist in those endeavors, and we are pleased to announce a new feature of available on this website. For each and every freshwater bivalve name (valid or not), we provide the history of citations we have captured from the literature.

For example, on the specimens page for the valid species Indonaia caerulea, we not only provide a map of specimen records but also the taxonomic history since 2007. That history documents the various names and combinations used since our 2007 checklist for this species and all of its synonyms, and links are provided to the individual references.

By clicking the link to the nominal species, you can find the synonymy for Indonaia caerulea. Typically, the nomina in a synonymy are listed strictly chronologically. On our site, we list the names by how recently they were regarded as valid. This moves the most interesting names to the top of what can be a long list (e.g., the synonymy of Anodonta anatina). For each name we provide a complete cresonymy — the history of name usage for that nomen.

So there it is. For any freshwater bivalve species on our web site, you can see not only how we classify it and circumscribe the often-numerous synonyms. And, you get the taxonomy that is the basis for our usage as well as potential alternative classifications. We don’t know of another mollusk database or any source since Simpson (1900) that provides such comprehensive taxonomic data on freshwater mussels!

February 2020

MonodacnaMonodacna colorata (Cardiidae, North Eurasia)

The February 2020 Mussel of the Month is Monodacna colorata. Monodacna (Family Cardiidae) is not actually a mussel taxon. It is a genus of mostly brackish-water species found in the Caspian and Black Seas with only one or two species living in freshwater.

This month, especially for Valentine’s Day, we are featuring Monodacna colorata, a cockle in the veneroid family Cardiidae. “Cardium” is greek for “heart,” so the tie-in with 14 February isn’t too much of a stretch. This “Mussel” of the Month can also serve as a reminder that the MUSSELp database serves information about freshwater bivalves generally. Those data are based on the review by Graf (2013). Obviously, the site is biased toward freshwater mussels, but the less consequential bivalves are there as well.

With the online version of the MUSSELpdb, the easiest way to find out what taxa we serve — besides using the site-specific Google Search — is to follow the “all genera” link.

January 2020

UtterbackianaUtterbackiana suborbiculata (Unionidae, North America)

The January 2020 Mussel of the Month is Utterbackiana suborbiculata. Utterbackiana is a genus of five species from eastern North America.

The genus Utterbackiana was described by Frierson (1927), but it was largely forgotten until Williams et al. (2017) brought it back for U. suborbciulata (type sp.), U. couperiana, U. hartfieldorum, U. heardi, and U. implicata. There has been no classic revision (evaluating synonyms, etc.), but the use of Utterbackiana is supported by recent molecular phylogenetic work.

(This is a long post with lots of Dillon-esque footnotes, so you might want to pause to fill up your coffee before you continue.)

It is worth reviewing how we got to this generic revision for a group of relatively well-studied North American mussels. The story technically begins at the end of the 18th century when Lamarck (1799) described the genus Anodonta, and the name was widely applied around the world. Then a bunch of stuff happened ... blah blah blah ... and Hoeh (1990) took up the problem of Anodonta sensu lato in Europe, western North America, and eastern North America. Using allozyme data (reanalyzed by Zanatta et al., 2007), it was reported that those species belonged to three separate clades that were recognized as genera: Pyganodon (like P. grandis) and Utterbackia (e.g., U. imbecillis) in eastern North America, and Anodonta in Europe (e.g., A. cygnea), western North America (A. kennerlyi), and Eastern North America (“A.” suborbiculata and “A.” couperiana). This new taxonomy was soon taken up by the freshwater mussel illuminati (e.g., Cummings & Mayer, 1992; Williams et al., 1993; Turgeon et al., 1998), and that taxonomy carried us into the 21st century.*

By the early 2000’s, hindsight had revealed that the Hoeh (1990; Zanatta et al., 2007) analyses were flawed. The ingroup consisted solely of species from Europe and North America then classified as Anodonta (like the species listed above), and Lasmigona (from North America) comprised the outgroup. As now understood, the eastern North American anodontines (including Pyganodon, Utterbackia, and Lasmigona) form a clade (Graf & Ó Foighil, 2000; Chase et al., 2018). Thus, a monophyletic Anodonta that includes species from eastern and western North America and Europe was only achieved by biased taxon sampling and a misplaced root on the cladograms.** Biogeographically, that kind of a distribution for Anodonta isn't well supported either since few genus-level clades are known to be shared across both sides of the Rocky Mountains in North America and Europe.***

This brings us to 2007 and the Graf & Cummings checklist (like so many of these tales often do). When considering only the species of North America — as Williams et al. (1993) and Turgeon et al. (1998) did — the difficulties with the taxonomy and biogeography of the local Anodonta species are somewhat smoothed over.**** But taking on the scope of all freshwater mussels and new knowledge gained from phylogenetic studies, it was evident to us (Graf & Cummings, 2007) that the “Anodonta” of eastern North America shared a more recent common ancestor with mussels in eastern North America than with Anodonta species in either the American West or Europe.

Fortunately, previous taxonomic opinions provided a solution. Hoeh (1990) didn’t invent the genus-level taxonomy of the former Anodontas. Rather, those names had been used previously as subgenera (Johnson, 1972, 1980; Heard, 1975) — e.g., A. (Pyganodon) grandis, A. (Utterbackia) imbecillis, A. (Utterbackia) couperiana, and A. (Utterbackia) suborbiculata. Putting U. couperiana and U. suborbiculata in Utterbackia solved the nonsensical eastern Anodonta problem, allowing the taxonomy to reflect a clade of eastern North American anodontines (Alasmidontina), although the relative phylogenetic positions of U. imbecillis and U. suborbiculata were not well understood at the time.

The relative positions of U. imbecillis and U. suborbiculata are better understood now: Utterbackia imbecillis, U. peggyae, and U. peninsularis comprise a clade (frequently sister to Pyganodon), and Utterbackiana suborbiculata and the other species represent a distinct clade (Breton et al., 2011; Smith et al. 2018). And thus explains the resurrection of Frierson’s (1927) long unused genus name.*****

* This discussion is limited to the North American taxa. The name Anodonta has been, until recently, applied to Anemina and Sinanodonta in East Asia.

** For example, if Quadrula had been used to root the tree and more eastern North American anodontine genera were included (e.g., Strophitus, Alasmidonta),† then we would expect the “Anodonta” species of eastern North America to be in a clade with Pyganodon, Utterbackia, and Lasmigona rather than European Anodonta. But that is a lot of “ifs.”

† And, assuming we could expect allozymes to behave like DNA to recover phylogeny.

*** Margaritifera being, perhaps, the main exception. Check out our discussion of Gibbosula for that whole other story.

**** The story of Ortmanniana and Actinonaias is analogous. “Actinonaias” ligamentina makes sense if you ignore the Central American species.

***** This post is long enough, so we won’t get into the curious coincidence of F.C. Baker (1927) and Frierson (1927) simultaneously naming new, closely related genera for William Utterback.

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