Page last updated
4 January 2013
Mussel of the Month
The 2012 Mussels of the Month.
Trapezoideus exolescens (Unionidae, Indotropical)
The December 2012 Mussel of the Month is Trapezoideus exolescens. Trapezoideus is a genus of only four species from southern and southeastern Asia.
The last Mussel of the Month of 2012, Trapezoideus exolescens, is dedicated to Mr. John M. Pfeiffer III in honor of the defense of his master's thesis at the University of Alabama. John has spent the last couple years exploring the phylogenetic relationships of southeast Asian freshwater mussels, and Trapezoideus has figured prominently in his research.
Trapezoideus is one of the five genera of tropical Asia freshwater mussels reported to have asymmetrical glochidia (Ortmann, 1916; Panha & Eongprakornkeaw, 1995; Deein et al., 2008).The asymmetry of the larva is the result a pronounced flange (appendix, appendage, process, hook, &c. &c.) on only one of the valves. As John explained last summer in an award-winning presentation to the American Malacological Society, these genera are polyphyletic. That is, this odd larval morphology appears to have evolved more than once in the same geographical area. However, there are more interesting twists to this story. Watch this site for updates, and we will let you know when the paper on the subject is published.
Lanceolaria grayana (Unionidae, Palearctic)
The November 2012 Mussel of the Month is Lanceolaria grayana. Lanceolaria is a genus of 7 species in eastern Asia.
Lanceolaria is an easily recognizable and widespread genus, distributed from eastern Russia south to Vietnam. It is an interesting genus to us as a representative of the subfamily Unioninae – the most easily recognized subfamily of the Unionidae.
Bouchet & Rorcoi (2010) recently took the bull by the horns and established seven subfamilies for the Unionidae, the most species-rich family of freshwater mussels: Unioninae, Ambleminae, Gonideinae, Rectidentinae, Parreysiinae, Coelaturinae, and Modellnaiinae. This was definitely an improvement over the two-subfamily-and-many-many-incertae-sedis-genera system we had punted with earlier (Graf & Cummings, 2006, 2007). Since 2010, Whelan et al. (2011) refined this new system somewhat by revising the Coelaturini as a tribe within the Parreysiinae, and this taxonomy is definitely something we can work with.
While the new classification established the subfamilies, the actual generic constituents of those taxa was indicated only by the synonymy of family-group level names. As far as we know, ours is the only list assigning all genera to these new subfamilies, although some are certainly guesses or placed by process of elimination. The challenge of these new subfamilies is that we really don’t have a good handle on the characters that diagnose them. We have had to rely on geography (Ambleminae), molecular characters (Parreysiinae), monotypy (Modellnaiinae), and intuition (Gonideinae, Rectidentinae).
But, among the subfamilies, the Unioninae is a shining star of recognizability. Members of this clade are diagnosed by hooked-type glochidia, and they consistently present an ectobranchous marsupium (i.e., they brood in the outer demibranchs). The placement of Lanceolaria among the Unioninae has also been supported by its frequent inclusion in phylogenetic analyses (Huang et al., 2002; Zhou et al., 2007; Ouyang et al., 2011).
We have optimism for the new classification of the Unionidae. What we are still waiting on is confidence.
Epioblasma capsaeformis (Unionidae, Nearctic)
The October 2012 Mussel of the Month is Epioblasma capsaeformis. Epioblasma is a genus of 22 species endemic to eastern North America.
A few years ago, we selected Epioblasma as Mussel of the Month just because sexually dimorphic mussels like these are so cool. Since we last checked in with this genus, some new taxa have been described (Jones & Neves, 2010). And, E. capsaeformis has recently been in the news, thanks to the re-stocking efforts of the Alabama Aquatic Biodiversity Center. Friend-of-the-MUSSELp Paul Johnson submitted the following report on 27 September 2012:
"Thanks to folks at the Freshwater Mollusk Conservation Center at Virginia Tech (VPI) in Blacksburg, VA for the donation of 1,007 Epioblasma capsaeformis (Oyster mussel). These 18-month, post-transformation animals were reintroduced into the Paint Rock River (Jackson County), yesterday afternoon.
"Culture efforts for the Oyster Mussel went exceptionally well last year, and VPI had more than 17,000 animals in absolutely beautiful condition. They had produced more than enough to support recovery activities in Tennessee and Virginia. The remainder were donated to ADCNR in support of reintroduction activities in Alabama. The brood stock for the effort came from 20 Clinch River females (Tennessee Broodstock - TWRA). The Oyster Mussel is federally endangered and the Clinch River retains the last robust population. Historically it occurred throughout the upper-middle Tennessee River system (to Mussel Shoals).
"The Oyster Mussel was last collected in the Paint Rock River basin by David H. Stansbery (Ohio State University Museum – 39533) on October 2, 1976 from the Larkin Fork.
"This was the 2nd reintroduction effort for the Paint Rock this year. In July, the AABC released federally endangered Cumberland Bean (Villosa trabalis) to the Paint Rock River (photo). Cumberland Bean was cultured by the AABC from brood stock donated by TWRA. The Cumberland Bean occurs in a short stretch of the Hiwassee River in TN, and is the last place the species occurs in any numbers in the Tennessee River basin (a few Cumberland River basin sites remain). A total of 269 individuals were released at the same locality on the Paint Rock. These were produced in 18 months of culture efforts from glochidia obtained from 5 gravid females."
Congratulations to Paul, the AABC, and the folks at VPI for a job well done!
Lasmigona complanata (Unionidae, Nearctic)
The September 2012 Mussel of the Month is Lasmigona complanata. Lasmigona is a genus of eight species, widespread in eastern North America.
In honor of the MUSSEL Project Web Site moving to the University of Wisconsin-Stevens Point (see the latest news), we have chosen a Mussel of the Month described from Wisconsin: Lasmigona complanata (Barnes, 1823).
D.W. Barnes (1823) described 26 species of freshwater mussels, many from the Interior and Great Lakes basins of North America. A good number of those names were in common usage during the 19th and early 20th centuries -- during the period when the works of Rafinesque (1820, 1831, etc.) were ignored as so much jibba jabba. Once Frierson (1927) and others championed the recognition of Rafinesque's taxa, only a few of mussel names introduced by Barnes retained their priority: Lasmigona complanta and Toxolasma parvum.
Chelidonopsis hirundo (Iridinidae, Afrotropical)
The August 2012 Mussel of the Month is Chelidonopsis hirundo. Chelidonopsis hirundo is a monotypic genus endemic to the Congo Basin of Africa.
We have already spotlighted Chelidonopsis as Mussel of the Month back in March 2005. But, the IUCN as recently highlighted this freshwater mussel as an Amazing Species. And, we know a little more about this species than we did 7 years ago. For example, while sampling in Malebo Pool in 2006, we collected some live C. hirundo. Unlike the unionids of North America and Europe, iridinids like Chelidonopsis have full-on siphons -- with mantle fusion more like a marine clam. While rooting around in the mud, KSC was injured by the sharp tail-fins of this really interesting shell.
Barynaias caldwellii (Unionidae, Neotropical)
The July 2012 Mussel of the Month is Barynaias caldwellii. Barynaias is a genus of five species in Central America.
With previous Mesoamerican Mussels of the Month, like Psoronaias and Nephronaias, it has been difficult to find something interesting to write. We know so little about what is actually quite a rich assemblage.
We don't know much more about the species of Barynaias. BUT we did find this interesting tidbit from Isaac Lea (1860) in his description of B. caldwellii:
"A single specimen was brought by Dr. Caldwell from his perilous expedition on the Isthmus of Darien with Lieut. Strain, and these molluscs formed part of the food on which the party subsisted."
We appreciate that these intrepid explores, in their state of hardship, remembered to bring one back for us to enjoy!
Pseudanodonta complanata (Unionidae, Palearctic)
The June 2012 Mussel of the Month is Pseudanodonta complanata. Pseudanodonta is a European genus of three species.
In contrast to mussel-rich temperate North America, the European freshwater mussels are relatively genus- and species-poor -- at least based on the current classification. However, recent research has indicated that the western Palearctic diversity is under-estimated and the taxonomy is evolving to reflect this.
For example, at the beginning of the present millennium, the genus Pseudanodonta was thought to be represented by a single species, P. complanata, and several subspecies (Falkner et al. 2001, 2002). Well, except that the Russian Comparatory School of Malacology regarded the genus to be composed of 5 species (Graf, 2007). Nowadays, we list three species in Pseudanodonta, and we ignore the Russian classification.
The biggest challenge to revising the classification of European freshwater mussel species is the excess number of genus and species names (and associated type specimens) that need to be accounted for. More than 60 species names have been introduced for Pseudanodonta, but that is still not enough for inclusion in the top 10 over-named species! To contribute at least some progress on this front, we have recently published on the genus (Graf, 2010) and species (Graf, 2011) of the 19th century French "New School," the most superfluous of the freshwater mussel super-nominators.
Lamellidens marginalis (Unionidae, Indotropical)
The May 2012 Mussel of the Month is Lamellidens marginalis. Lamellidens is represented from Afghanistan to Burma and north to Nepal by eleven species.
For many tropical freshwater mussel species, very little known except that they exist. For examples, see previous Mussels of the Month: Unionetta, Ctenodesma, Rectidens, etc. Lamellidens, in contrast, is an important model mussel for physiological research. More than a dozen papers have been published since 2011 that mention "Lamellidens" in the title. Most of those have to do with toxicology and accumulation of metals.
We are more interested in Lamellidens as a member of the Parreysiinae. We recently resolved that subfamily composed of freshwater mussels from Africa and southern Asia (Whelan et al., 2011). As far as we can see today, the Parreysiinae is represented by 4 tribes: Coelaturini (Africa), Oxynaiini (S and SE Asia), Parreysiini (S Asia) and Lamellidentini (S Asia). Lamellidens is the only genus of the last of these, and it represents the most basal member of the clade. Of course, only two species of Lamellidens have been analyzed to-date, and there is certainly more room for systematic studies of southern Asian mussels.
Fusconaia ebena (Unionidae, Nearctic)
The April 2012 Mussel of the Month is Fusconaia ebena. Fusconaia is a genus of about a dozen species found in eastern North America.
Fusconaia ebena is an interesting freshwater mussel for a couple reasons. One is that is that it was mentioned early on in a conservation context by Coker (1914). He predicted that the completion of the dam at Keokuk, IA would restrict the movement of Alosa chrysochloris (skipjack herring) and that Upper Mississippi mussels that rely on that fish -- like F. ebena -- would suffer. Early in the 20th century, F. ebena was quite common in Mississippi (Baker, 1928), but today, it merits government protection in many parts of its former range (Cummings & Mayer, 1992).
Another reason that Fusconaia ebena interests us is that, for the last decade or so, it has been hard to know to what genus this species belongs. Cladistic analyses by Lydeard et al. (2000) and Campbell et al. (2005) resolved F. ebena in various positions, usually quite distant from other Fusconaia species but without much in the way of support. Campbell & Lydeard (2012) have recently codified this lack of resolution by erecting a new genus for F. ebena, Reginaia.
As we discussed a couple months ago for Pleuronaia, Reginaia is based solely on mitochondrial DNA. This classification-hypothesis is difficult to reconcile with Ortmann's (1912) report that he found Fusconaia ebena difficult to separate from F. subrotunda using either shell or soft anatomical characters. Moreover, while multiple phylogenetics studies have reported Fusconaia polyphyly, they are all re-analyses of the same three (!) individuals. It is difficult to understand how to extrapolate classification from weak results based on such limited sampling.
For the time being, the MUSSEL Project Database will maintain the use of Fusconaia for F. ebena. When more information becomes available, the genus name Reginaia may indeed be appropriate for this species. However, we do not think it is a good idea to name clades just for the sake of naming them. Instead, we would like our classification to have a little more explanatory power. Fusconaia turns out to not be that useful either, but it has the current advantage of prevailing usage.
We look forward to re-visiting this topic when some synapormorphies have been identified and the position of "Reginaia" ebena among the eastern North American Unionidae is better resolved.
Antediplodon carolussimpsoni (Hyriidae, Nearctic, Triassic)
The March 2012 Mussel of the Month is Antediplodon carolussimpsoni. Antediplodon is a genus of freshwater mussels of the Upper Triassic of North America.
To highlight the inclusion of fossil taxa into the MUSSEL Project Database, this month we have selected our first fossil as the March Mussel of the Month.
Anyone that wants to have a comprehensive understanding of freshwater mussel evolution is going to have to account for the fossil diversity. Though perhaps obvious, that desire has yet to be put into practice. The biggest obstacle to neo-paleo-synthesis is that the most valuable characters for classifying living species (i.e., soft-anatomy, larvae, behavior, DNA) are almost completely missing from the fossil record. The modern paleontological literature, by necessity, relies on shell characters. This makes it difficult to convincingly assign ancient specimens to the correct family. In some cases, even a realistic genus is unavailable. For example, many North American fossil species are still assigned to Unio. Not because of any hypothesized affinity to the modern Old World taxon, but because no meaningful alternative has been introduced.
For example, Antediplodon (from the Upper Triassic, 228-200 Mya) has been assigned to the Hyriidae because shell sculpture is similar to that of some modern hyriids. But, as Modell (1964) proved by concocting a shell-based classification that nobody follows, shell characters suffer convergent evolution worse than some other, more reliable traits. Just because two freshwater mussels have similar looking shells doesn't mean they are closely related. And, conversely, just because two freshwater mussels have different looking shells doesn't mean that they aren't closely related.
Since we don't have a better place to put Antediplodon, we will leave it in the Hyriidae, just like Modell (1957). It is interesting to note that the earliest members of the Unionoida in North America belong to family that is now limited to South America and Australasia. This is all made even more interesting my the work of Skawina & Dzik (2011) which suggests that Triassic unionoids are stem-group taxa rather than part of the extant crown group.
Pleuronaia barnesiana (Unionidae, Nearctic)
The February 2012 Mussel of the Month is Pleuronaia barnesiana. Pleuronaia is a genus of three species endemic to the Cumberland Plateau in eastern North America.
Pleuronaia is a relatively new genus concept in North America. The taxon was originally introduced by Frierson (1927) and parroted by Haas (1969), but the genus name was never in wide use.
The change came following the comprehensive phylogenetic analyses by Campbell et al. (2005). Pleuronaia is made of parts of Fusconaia, Pleurobema and the now-out-of-use genus Lexingtonia. The species currently included in Pleuronaia are not identical to those originally placed in the genus by Frierson, and diagnostic morphological synapomorphies have not been identified (Williams et al., 2008). Instead, Pleuronaia is applied merely as the oldest available genus name for a clade recovered by a single mitochondrial analysis.
It is significant that taxonomic revisions occur even among the best studied freshwater mussels in the world. We look forward to seeing how the classification can be further improved to reflect evolutionary relationships.
Prohyriopsis stolata (Unionidae, Indotropical)
The January 2012 Mussel of the Month is Prohyriopsis stolata. Prohyriopsis is a monotypic genus known only from Sumatra.
Prohyriopsis stolata is another freshwater mussel about which we know just about nothing. Martens (1900) described it as Unio stolata from Lake Danau-Baru in Sumatra, Haas (1914) made up a new genus name for it, and since then it has barely been acknowledged.
Unfortunately, this amount of data is typical of many taxa from the Malay Archipelago.