Mussel of the

Page last updated
1 December 2009

Mussel of the Month

The 2009 Mussels of the Month.

December 2009

Tamsiella tamsianaTamsiella tamsiana (Mycetopodidae, Neotropical)

The December 2009 Mussel of the Month is Tamsiella tamsiana. Tamsiella is a genus of two Neotropical species: one from the Orinoco and one from the Upper Amazon.

Almost nothing is known about the genus Tamsiella. A Google web search merely provides links to taxonomic databases, and Google Scolar returns only four hits! The genus is represented by two species: T. tamsiana in the Orinico Basin and T. amazonica in the upper Amazon.

November 2009

Fusconaia flavaFusconaia flava (Unionidae, Nearctic)

The November 2009 Mussel of the Month is Fusconaia flava. As we currently recognize it, Fusconaia is a North American genus of 15 species. That assessment is likely to change as revisions proceed.

Early in the 20th century, most of the red-bodied, tetrabranchous species of the Pleurobemini we sequestered into the genus Fusconaia to acknowledge their distinction from Pleurobema, Elliptio, etc. Recent phylogenetic work has brought that arrangement into question (Campbell et al., 2005), but the issue is far from settled. In our checklist (Graf & Cummings, 2007), we kept all the historical species of Fusconaia together for lack of a better solution. But we can sweep all that under the rug for the moment to talk about Fusconaia flava. That species is the type of the genus, and so it will remain a Fusconaia no matter what happens its current congeners (assuming Fusconaia isn't sunk altogether!).

F. flava is a widespread freshwater mussel that is found in a variety of habitats, and its conchological variation typifies a phenomenon known as Ortmann's Law of Stream Position. A.E. Ortmann (1920) was among the earliest to systematically investigate the relationship between infraspecific morphological variation in mussels and stream size. In summary, Ortmann found that, within single widespread species like F. flava, as one samples upstream or downstream, shell morphology changes in a predictable way. Toward the headwaters, shells tend to be more laterally compressed and elongate, with centrally placed centrally. Individuals occupying larger rivers will be more obese and trigonal, with high umbos shifted to the anterior.

Fusconaia flava is not the only species exhibit this common pattern, suggesting a common mechanism. Watters (1994) has shown that the obese big-water shell morphology serves as a better anchor in the lamellar flow of a big river, whereas the upstream form is a better burrower. DLG (Graf, 1997) documented the pattern of gradual change in shell morphology from one extreme environement to the next.

October 2009

Inversidens brandtiiInversidens brandtii (Unionidae, Palearctic)

The October 2009 Mussel of the Month is Inversidens brandtii. Inversidens is a genus of two species, found in Japan, China, and eastern Russia.

Inversidens is currently thought of as consisting of only two species. Formerly, however, it was regarded to have as many as six species (Haas, 1969). Improvements in data beyond just conchological similarities have inspired several revisions, resulting in the former Inversidens being split into three different genera: Inversidens, Inversiunio, and Pronodularia. Since we published our global checklist (Graf & Cummings, 2007), new species have been described in both Inversiunio and Pronodularia. Furthermore, the Russian Comparatory School of Malacology has has also weighed in and recognized numerous species that no one else sees. We don't regard their special brand of splitting to be that helpful.

September 2009

Diplodon chilensisDiplodon chilensis (Hyriidae, Neotropical)

The September 2009 Mussel of the Month is Diplodon chilensis. Diplodon is a large South American genus of eighteen species.

The historic concept of Diplodon (as applied by Parodiz, 1968 and Haas, 1969, for example) has recently been split into two genera: Diplodon s.s. and Rhipidodonta. This division is based upon the somewhat dubious character of whether or not the glochidia are parasitic upon fish. We would like to learn more about the evidence supporting non-parasitic life cycles for the several species currently placed in Rhipidodonta (Simone, 2006), but that is not what this Mussel of the Month is about.

The species diversity of Diplodon (+ Rhipidodonta) has traditionally been among the hardest questions to answer in the field of "uniöology." Until recently, the only two genus-wide treatments had been those of Parodiz (1968) and Haas (1969). Unfortunately, the two systems that they came up with were completely incompatible. This left us in a quandary for some time while we were compiling our global species checklist (Graf & Cummings, 2007): how to deal with the species of Diplodon? Fortunately, we were saved by the recent, nearly continent wide system proposed by Simone (2006).

As we said at the time (Graf & Cummings, 2007: 299),

"We hope our discussion and checklist of global freshwater mussel diversity will have the same effect that Simpson's (1900, 1914) did a century earlier: interest and discussion in the Unionoida will increase ..., and new data and analyses will test and refine the patterns we have described."

The online version of our checklist, Unionoida cum Grano Salis, can be found by clicking here.

Diplodon chilensis is one species that has since been revised. We listed D. chilensis and D. patagonicus as two separate species, from the western and eastern sides of the Andes in Chile and Argentina, respectively. But as explained by Parada & Peredo (2008), this arrangement as been regarded as incorrect for most of the 20th century! Rather, most systemists have regarded the eastern population as merely a subspecies, D. chilensis patagonicus.

We have updated our checklist to reflect this hypothesis, and we look forward to seeing where others can improve our understanding of freshwater mussel diversity by showing us how our assessment was incorrect.

August 2009

Mweruella mweruensisMweruella mweruensis (Unionidae, Afrotropical)

The August 2009 Mussel of the Month is Mweruella mweruensis. Mweruella is a monotypic genus endemic to Lake Mweru in Africa.

The Mussel of the Month is late this month because DLG was away to Lake Mweru in Zambia looking for live specimens of this very mollusk, so what better reason to recognize it for August 2009!

The taxonomy for this mussel is somewhat confused (or at least, we hypothesize that it is confused until we have more data to convince us otherwise). Everything about the outward appearance of M. mweruensis looks like it belongs in the large, garbage-pail genus Coelatura. Haas was the first one to single out this species as a subgenus, but it was Pain & Woodward (1968) that really tried to make a case for its uniqueness. They argued that,

"... since it differs from other African Unionids in details of its shell morphology and anatomical features, [it] is placed in a new subfamily Mweruellinae."

The anatomical feature to which Pain & Woodward referred was the fact that in the specimen(s) they examined, females brooded in only the inner demibranchs as opposed to all four like Coelatura. As far as the species unique conchology, they noted,

"... umbonal sculpture consisting of well developed radial plications highly reminescent of those of the South American genus Tetraplodon Spix (= Castalia of authors non Lamarck)... ."

For the record, the specimens that we have seen (including the type pictured on this page) looking nothing like any species of Castalia. Some specimens do have weak umbonal sculpture, typical of Coelatura species of the region. Until now, we have not had any preserved specimens with soft-parts to confirm Pain & Woodward's other observations. However, DLG got a bunch in Lake Mweru this year, and we are looking forward to including them in future phylogenetic and anatomical studies.

July 2009

Psoronaias semigranosaPsoronaias semigranosa (Unionidae, Neotropical)

The July 2009 Mussel of the Month is Psoronaias semigranosa. Psoronaias is a genus of eight species found in Central America.

We don't have too much to say about P. semigranosa or the other species of Psoronaias. The taxonomy of the genus dates from Frierson (1927) and Haas (1969), and so modern species concepts have not really been taken into consideration. This is a general problem with the taxonomy of Mesoamerican freshwater mussels.

While malacologists have been largely silent on the subject of Psoronaias for the last 50 years or so, the archeological community has been making some progress. For example, Emery (2008) reported that species of Psoronaias (and other freshwater mollusks) were used as food by the Mayan people of Guatemala.

June 2009

Epioblasma flexuosaEpioblasma flexuosa (Unionidae, Nearctic)

The June 2009 Mussel of the Month is Epioblasma flexuosa. Epioblasma is a highly endangered genus of 20 species found in eastern North America.

Over the last few years there has been quite a burst of activity to study the remaining species of the genus Epioblasma. This is not too surprising as many of the species are extinct, the remaining species are under state and/or federal conservation protection, and they are REALLY interesting from a biological perspective. It is this last aspect that we want to focus on here.

Epioblasma species, like many other lampsilines, are sexually dimorphic. That is, males and females look different from each other, aside from morphological differences in their reproductive structures. Specifically, many lampsilines have sexually dimorphic shells. This may seem trivial since lots of taxa are sexually dimorphic: e.g., cardinals and bighorn sheep. However, the difference in this case is that males of those species use those morphological traits to compete for mates (i.e., sexual selection). Freshwater mussels don’t copulate or physically interact with each other (as far as we know), so what difference could it make to one Epioblasma what another one looks like?

It turns out that the shells of female Epioblasma species are reproductive structures. On Chris Barnhart’s Unio Gallery, you can see some jaw-droppingly cool video of various mussels (not E. flexuosa, but other species) using their shells to grab and hold their host fish. If that doesn’t blow your mind, then you should think about it some more.

May 2009

Germainaia geayiGermainaia geayi (Unionidae?, Afrotropical)

The May 2009 Mussel of the Month is Germainaia geayi. Germainaia is a possibly bogus genus of one species reported from Madagascar.

We described Germainaia as a new genus last month (Graf & Cummings, 2009). As we said on our project page about the freshwater mussels of Madagascar:

"Germainaia geayi is known only from 2.5 specimens with the vague locality "Madagascar." The species was originally described as "Unio (Nodularia) geayi" by Germain (1911). Most subsequent treatments, however, have put G. geayi in the genus Coelatura. Unio, Nodularia, and Coelatura are all genera assigned to the family Unionidae. However, we aren't completely convinced that the available material actually belongs to that family.

"Upon first inspection of the type when we were in Paris in 2006, that specimen struck us as more similar to a hyriid, like one might find in Australia or New Zealand (such as Hyridella depressa). While members of the Unionidae and the Hyriidae can be readily distinguished based upon their soft-anatomy, we have had trouble when it comes to family-level shell synapomorphies.

"Given the scanty material available for G. geayi and the conflicts it presents to going biogeographical hypotheses, we regard Germainaia as incertae sedis at the family level.

April 2009

Hyridella depressaHyridella depressa (Hyriidae, Australasia)

The April 2009 Mussel of the Month is Hyridella depressa. Hyridella is a genus of eight species found throughout Australasia.

Hyridella is the most diverse and widespread of the Australasian freshwater mussel genera, with five species on Australia, two on New Guinea and the Solomon Islands, and even one in New Zealand. However, that last one is probably just a taxonomic legacy. All the other New Zealand "Hyridella" have recently been moved to Echyridella, and the same will probably happen to H. aucklancica (Fenwick & Marshall, 2006; Graf & Cummings, 2007).

March 2009

Cafferia caffraCafferia caffra (Unionidae, Afrotropical)

The March 2009 Mussel of the Month is Cafferia caffra. Cafferia is a monotypic genus from southern Africa.

Cafferia caffra is an interesting freshwater mussel for at least two reasons. For one, belongs to the Unio-group of genera (Unionini), as evidenced by its hooked-type glochidia (Heard & Vail, 1976; Graf & Cummings, 2006a). There are other such unionines in Africa, but none in Subsaharan Africa. Unio mancus and U. abyssinicus are limited to the Nile Basin. This suggests (to us, anyway) at least two separate invasions of Africa by the Unionidae from the north: the progenitors of Coelatura, etc. with their unhooked-type glochidia and the Unio-group, represented by Cafferia.

C. caffra also has a unique distribution pattern. It is found throughout southern Africa, but it reaches its northern limit in the Zambezi and Kafue rivers, including above Victoria Falls (Appleton, 1979; Graf & Cummings, 2006b) The distribution of this freshwater mussel is consistent with its occurrence in the ancient Lake Makgadikgadi.

February 2009

Theliderma cylindricaTheliderma cylindrica (Unionidae, Nearctic)

The February 2009 Mussel of the Month is Theliderma cylindrica. Theliderma is a genus of six species endemic to eastern North America.

In most sources where one might look up the classification of this month's Mussel of the Month, you would find it identified as "Quadrula cylindrica" (Cummings & Mayer, 1992; Williams et al., 1994; Williams et al., 2008). However, based upon a recent phylogenetic analysis (Serb et al., 2003) and a generic revision (Graf & Cummings, 2007), we think this mollusk might be better served under the name Theliderma cylindrica. We provided more detail about this nomenclatural shift when Quadrula had its month.

T. cylindrica is widespread in the interior basin of the southern United States (occurring on both sides of the Mississippi River), and the species is also know as far north as the Maumee Basin in the Great Lakes. Interestingly, T. cylindrica is absent from the Upper Mississippi.

T. cylindrica is considered threatened throughout its range (Williams et al., 1993). Two subspecies are recognized: T. c. strigillata from the Upper Tennessee System and T. c. c. from everywhere else (Williams et al., 2008).

January 2009

Caudiculatus caudiculatusCaudiculatus caudiculatus (Unionidae, Indotropical)

The January 2009 Mussel of the Month is Caudiculatus caudiculatus. Caudiculatus is a monotypic genus endemic to the island of Borneo.

Caudiculatus caudiculatus is a little, brown, poorly-known freshwater mussel known only from Borneo, in the East Indies. We don't have much to say about it other than we have it on good authority that it exists (or at least that it existed) (Graf & Cummings, 2007).

The Treatise on Invertebrate Paleontology reports that Caudiculatus has no known fossil record (Haas, 1969b).

The internets don't have much more to say about it. A google search reveals a few pages that lists its name (e.g., DiscoverLife, Mussel Genera of the World), a google books reference to Simpson (1914), a few hits to various pages on our web site, and then lots of links to other organisms that go by the same trivial name.

Who wants to go look for mussels in Borneo?!

2009 MUSSELp Postcard
2009 MUSSELp Mussels of the Month Postcard.
Click here for a high-resolution jpeg.

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