Mussel of the

Page last updated
5 January 2015

Mussel of the Month

The 2014 Mussels of the Month.

December 2014

InversiunioInversiunio reinianus (Unionidae, Palearctic)

The December 2014 Mussel of the Month is Inversiunio reinianus. Inversiunio is a genus of four species found in Japan and Korea.

Back in October 2009, we discussed the problem of Inversidens sensu lato. In Haas's (1969) conchological view, that genus was composed of 6 species from eastern Asia and Japan. However, it was subsequently discovered that two different larval morphologies were represented among those species. Whereas as shell morphology (outline, umbo position, sculpture, etc.) is highly variable, often convergent, and well known to confound a natural classification, structures of glochidium-type larvae can be downright diagnostic.

In the the particular case of Inversidens sensu lato, some species (e.g. I. brandtii) have glochidia lacking marginal hooks. That doesn't tell us much about classification since most unionid freshwater mussels have unhooked type glochidia. But, other species (like I. reinianus) have glochidia with marginal hooks. In the family Unionidae, only members of the subfamily Unioninae have hooked-type glochidia. Thus, Inversidens sensu lato was composed of representatives of (at least) two different subfamilies. To solve this problem, the genus Inversiunio in the subfamily Unioninae was created (Habe, 1991). Inversidens is currently placed in the Gonideinae.

The separation of Inversidens sensu stricto and Inversiunio based on their divergent larval morphologies is not an isolated case. An analogous situation has also occurred with certain species formerly of the genus Lamprotula (also Gonideinae) being transferred to Aculamprotula (Unioninae) because of their hoooked-glochidia.

November 2014

CyrtonaiasCyrtonaias tampicoensis (Unionidae, Nearctic & Neotropical)

The November 2014 Mussel of the Month is Cyrtonaias tampicoensis. Cyrtonaias is genus of six species extending from southern Texas to Guatemala and Honduras.

Cyrtonaias is one of several genera of Central American freshwater mussels. It is distinguished from many of the mussels from that region in that its clearly lampsiline marsupial morphology allows it to be unabiguously classified all the way down to the tribe level. That is something.

But that isn't really what we want to talk about this month. With KSC away on a sampling adventure to the wilds of Brazil, DLG has taken this opportunity to update the online versions of the MUSSEL Project Database. It has been 15 months or so since the last update, and our synthesis has accumulated several changes. These include new specimen records from various museum visits, specimen identification updates (thanks especially to Karlo Nagel!), and a thoroughly revised and updated classification. Since the summer of 2013, we have been working to get our data into shape for inclusion in the ITIS web site database. The web version of the MUSSELpdb now reflects those changes as do the static (yet always changing) Unionoida cum Grano Salis pages.

October 2014

TriplodonTriplodon corrugatus (Hyriidae, Neotropical)

The October 2014 Mussel of the Month is Triplodon corrugatus. Triplodon is a genus of two species, distributed from northern South America through the Amazon basin.

Triplodon corrugatus is one of more than 70 species known from the region of northern South America, including the Amazon basin. Recently, KSC gave a presentation on the subject at the 7th Malacological Congress of the European Malacological Societies entitled, "The Freshwater Mussels (Bivalvia: Unionoida) of Northern South America and the Amazon." He discussed our systematic re-evaluation of the taxa of the region based on 1) fieldwork conducted by KSC in collaboration with Christine A. Mayer (1986-1995), 2) our collections-based study of specimens in 17 major research collections, and 3) a comprehensive literature review.

The 71 species of the region are classified in 16 genera and 3 families: Hyriidae (29 spp.), Mycetopodidae (40), and Etheriidae (2). Thirty-nine species are found in northern South America, 19 of which are thought to be endemics. Forty-four species are recognized from the Amazon Basin — 14 of which are endemics (46 & 19 including the Rio Tocantins).

The genus Triplodon is known only from a few drainages in Northern South America and the Amazon (including the Tocantins) with the exception of a disjunct population located near Victoria in the state of Espirito Santo, Brazil collected as part of the Thayer Expedition to Brazil conducted by the MCZ.

* 71 species according to us. Only 5 of these await description.

September 2014

ArcidensArcidens confragosus (Unionidae, Nearctic)

The September 2014 Mussel of the Month is Arcidens confragosus. Arcidens is a genus of two species in eastern North America.

Arcidens confragosus came to our attention due to the recent article by Inoue et al. (2014). The authors employed phylogenetic analysis of nuclear and mitochondrial DNA as well as a morphometric study of shell dimensions to examine the evolutionary relationship between A. confragosus and Arkansia wheeleri. Inoue et al. (2014) found these two species to be sister to each other and the genetic divergence between them very shallow. They concluded that these two species should both be classified as sister species in the genus Arcidens. This affinity was pointed out in the original description of Arkansia (Ortmann & Walker, 1912), their congeneric status was codified by Clarke’s (1981) revision of the Tribe Alasmidontini, and we advocated such an evolutionary classification in our global checklist (Graf & Cummings, 2007; this web site).

Given that no one has ever suggested that A. confragosus and A. wheeleri were anything but sisters (in the absence of molecular data, now available thanks to Inoue et al.), how is it that Ortmann & Walker (1912) felt A. wheeleri merited its own monotypic genus? The described differences were mostly conchological—A. wheeleri has a greater width, larger umbos and a different shell sculpture than A. confragosus. A. wheeleri also has a unique structure of the outer demibranch (Clarke, 1981). These are just the differences between two species. A priori, there is no basis to recognize (or not recognize) them as separate genera.

Back in 2007, even in the absence of explicit phylogenetic data, we synonymized Arkansia with Arcidens (Graf & Cummings, 2007). This was not done based on any hypothesis about the level of divergence between them. Rather, we found it uninformative to have monotypic sister genera. If everyone agreed that A. confragosus and A. wheeleri was each other’s closest relative, then why wasn’t this reflected in the classification? No information is lost by classifying the two species in the same genus (i.e., the phylogeny has the same number of branches), but the evolutionary affinity between the two is made explicit by the classification.

August 2014

NitiaNitia teretiuscula (Unionidae, Afrotropical)

The August 2014 Mussel of the Month is Nitia teretiuscula. Nitia is a genus 5 species found in West Africa, East Africa and the Nile Basin.

Nitia teretiuscula is found in the Nile Basin of Africa. What interests us about this mussel this month is that it served as the hard working sister-group to Coelatura and the other Afrotropical unionid species in a recent phylogenetic analysis.

DLG, Anthony Geneva, John Pfeiffer and Alex Chilala just published a new paper on the phylogenetic relationships of the mussels of Lake Mweru. The paper focuses on two monotypic genera, Prisodontopsis and Mweruella, and the upshot was that the two taxa are sister to each other (with some interesting complications). Graf et al. (2014) concluded that there was really just one genus with two species, Prisodontopsis aviculaeformis and P. mweruensis. With the help of Nitia to calibrate the molecular clock, they were able to determine a Pleistocene age for the divergence of the two Lake Mweru species. Lake Mweru doesn't have much of a fossil record, but Nitia is well known from the Rift Valley, which does (Van Damme & Pickford, 2010).

Let's all take this month and celebrate little Nitia teretiuscula, the horologer.

July 2014

MartensnaiasMartensnaias rubicunda (Unionidae, Neotropical)

The July 2014 Mussel of the Month is Martensnaias rubicunda. Martensnaias is a genus of one species known from one valve collected in Guatemala.

Martensnaias is another Mesoamerican freshwater mussel genus about which we know very little. The genus is known from a single species, and that species was described by Martens (1900) from a single valve (shown above). We have discussed the problem of our mussel-knowledge vacuum in Central America before (e.g., see Sphenonaias). You now know everything we know about this mussel, which is what was known by Frierson (1927) and Haas (1969): it allegedly exists.

With this Central American mussel out the way, we can now shift gears to talk about last months contributions to Neotropical freshwater musselology. From 22-27 June 2014, DLG, KSC and University of Stevens-Point student Caitlin M. Luebke attended in the Mollusca 2014: Encuentro de las Américas meeting in Mexico City. Our society (the American Malacological Society) and three others met jointly at UNAM to discuss mollusks and get out of the rain. Each of the MUSSELp participants gave a presentation. DLG and KSC each gave talks during the "Bivalves of the Americas" symposium — "OK, Let's Try This Again: A Re-Assessment of Global Freshwater Mussel Diversity (Bivalvia: Unionoida)" and "The Freshwater Mussels (Bivalvia: Unionoida) of Colombia, Venezuela, the Guianas and Suriname, South America," respectively. The highlight, though, was Ms. Luebke's poster (co-authored with Rachel Sommer, also of UWSP), "Curation of the Daniel Bereza Mollusk Collection at the Smithsonian National Museum of Natural History." She won an award for Best Student Poster at the meeting. Great work, Caitlin!

June 2014

DromusDromus dromas (Unionidae, Nearctic)

The June 2014 Mussel of the Month is Dromus dromas. Dromus is a monotypic genus endemic to the Cumberland Plateau in eastern North America.

Dromus dromas (notice the difference in spelling between the genus and species names!) is interesting for a couple of reasons — besides the fact it has not previously been selected as the Mussel of the Month. Simpson (1900) and Ortmann (1912) set Dromus apart from other freshwater mussel genera based on its unique combination of hard- and soft-anatomical characters: a shell like Cyprogenia but wrinkled marsupial demibranchs similar to Ptychobranchus. Ortmann (1912) illustrated that the wrinkles in the brooding gills manifest with size (i.e. age).

Whereas D. dromas is historically known from both the Cumberland and Tennessee River basins on the Cumberland Plateau, reproducing populations are currently known only from the Clinch and Powell Rivers (tributaries of the Tennessee). D. dromas was added to the U.S. Federal Endangered Species List in 1976, and Jones et al. (2004) made an interesting study of this mussel’s life history pursuant to the mussel's recovery.

May 2014

TihkiaTihkia (Triassic)

The May 2014 Mussel of the Month is Tihkia sp. Tihkia is a fossil genus of three known species from the Triassic.

This month's mussel is a Triassic fossil, possibly of the genus Tihkia. The choice was inspired by the recent visit of Dr. Aleksandra Skawina of the University of Warsaw to UWSP. From 14-18 April 2014, Dr. Skawina was funded by a grant from the EU to visit a "modern university" in the USA, and she chose to be hosted by DLG at the University of Wisconsin-Stevens Point. During her stay, Dr. Skawina attended various lectures and labs in the Biology Department, but she also found time to explore the mussel collection in the Graf Lab.

Dr. Skawina presented a well-received seminar on her research entitled "The Origin and Early Evolution of freshwater Mussels (Mollusca: Bivalvia: Unionoida), and Shell Biomineralization in Recent Unio." The lecture covered both her graduate work on Triassic freshwater bivalves (like Tihkia) and more recent research on the physiology of shell formation in modern mussels. It was inspring to have the opportunity to work with Dr. Aleksandra Skawina, and we look forward to continuing our collaboration with her.

April 2014

Utterbackia imbecillisUtterbackia imbecillis (Unionidae, Nearctic)

The April 2014 Mussel of the Month is Utterbackia imbecillis. Utterbackia is a genus of seven species found in eastern North America.

Utterbackia is an interesting mussel for a number of reasons — both with regard to its reproductive biology and the taxonomy of eastern North American species formerly (or currently) classified in the genus Anodonta. Those would be interesting angles from which to wax malacological, but instead we are going to talk about our research on Mexican freshwater mussels.

Over Spring Break last month, DLG, KSC, and three UWSP undergraduate collaborators — Charlie Jordan, Caitlin Luebke, and Rachel Sommer — traveled to the Smithsonian National Museum of Natural History in Washington DC. Our objective was to continue the work we started earlier this year on the Bereza collection. A substantial portion of this collection of freshwater mussels is an amazing diversity of specimens from three Mexican states. One of the specimen records that caught our attention was a specimen of Utterbackia imbecillis from the Rio Papaloapan. Previously, we had only known U. imbecillis from as far south as the Mexican tributaries of the Rio Grande. We anticipate that when we get all the data sorted out, we will have lots of new and interesting specimen records to report. So, watch this space!

March 2014

Cuneopsis celtiformisCuneopsis celtiformis (Unionidae, Indotropical)

The March 2014 Mussel of the Month is Cuneopsis celtiformis. Cuneopsis is a genus of six species occurring from the Yellow River south to northern Vietnam.

We chose Cuneopsis as this month's MotM in honor of the recently published book on Chinese freshwater mussels by Zhuang & Jing (2013). The last few weeks have been spent updating our local version of the MUSSEL Project Database to reflect this new taxonomic information, including 5 species new to science. It was interesting to learn how many North American freshwater mussel species have been introduced to China by pearl farmers. Those new data will make it to the online version of the MUSSELpdb the next time we update the data (probably early in summer 2014).

The taxonomic information in that book was surprisingly easy to accommodate into our database since, for the most part, the MUSSELpdb was apparently used as the basis for synonymies. Moreover, many of the figures are those featured on this web site. In truth, we would have expected explicit attributions when our pics or taxonomic data were used. Even better, it would have been appropriate to cite our relevant publications (Graf, 2007; Graf & Cummings, 2007, etc.) that form the backbone of this web site. Apparently, rather than being a resource to facilitate taxonomic research, the MUSSELpdb is now the source! We are glad to know that our research is being put to good use. We are also pleased to have our taxonomy "truthed" by local workers.

February 2014

Sphenonaias liebmanniSphenonaias liebmanni (Unionidae, Nearctic)

The February 2014 Mussel of the Month is Sphenonaias liebmanni. Sphenonaias is a genus of seven species that is found from the western Gulf Coastal Plain of Texas south to Nicaragua.

Traditionally, we have chosen Central American genera for the Mussel of the Month when we are in a rush to get something posted. If we choose animals about which little is known, then we have an excuse to write less. Our apologies if we have pulled back the curtain too much for you, but check out previous entries on Psoronaias, Barynaias, Micronaias, Nephronaias, Popenaias, Arotonaias, or Friersonia, and you'll see what we mean.

This month we have chosen Sphenonaias liebmanni from Mexico as a segue to talking about our recent collections visit to the Smithsonian National Museum of Natural History (USNM) in Washington DC. UWSP undergraduate Caitlin Luebke joined us* at the Museum Support Center to sort through what turned out to be an excellent collection of freshwater mussels from Mexico. Caitlin's work was funded by the Smithsonian through the efforts of our friend Dr. Robert Hershler, and this project continues the research she started last spring on the Daniel Bereza Collection.

We were amazed and delighted to work with such a magnificent haul of Mexican mussels. We look forward to returning to Washington during Spring Break to continue our taxonomic exploration of the poorly understood Central American mussel fauna.

* Actually, KSC was snowbound and missed the whole adventure.

January 2014

Leguminaia wheatleyiLeguminaia wheatleyi (Unionidae, Palearctic)

The January 2014 Mussel of the Month is Leguminaia wheatleyi. Leguminaia is a genus of two species endemic to the Middle East, from Syria and Turkey east to the Tigris-Euphrates.

Leguminaia wheatleyi is one of the 11 freshwater mussel species known from the Middle East — otherwise known as the southwest Palearctic (Graf, 2007). The following taxa occur in the region:

  1. Anodonta pseudodopsis Locard, 1883 *
  2. Anodonta vescoiana Bourguignat, 1856 *
  3. Leguminaia saulcyi (Bourguignat, 1852) **
  4. Leguminaia wheatleyi (Lea, 1862) **
  5. Margaritifera homsensis (Lea, 1865) *
  6. Potomida littoralis (Cuvier, 1798)
  7. Pseudodontopsis euphraticus (Bourguignat, 1852) **
  8. Unio crassus Philipsson in Retzius, 1788
  9. Unio mancus Lamarck, 1819
  10. Unio terminalis Bourguignat, 1852 *
  11. Unio tigridis Bourguignat, 1852 *

* species is endemic to the Middle East
** genus is endemic to the Middle East (Graf & Cummings, 2007)

We currently know very little about the systematics and biology of the lineages endemic to the region from Turkey and Syria east to the Tigris-Euphrates in Iraq. However, these animals are the topics of ongoing research. For example, Cek & Sereflisan (2010) recently investigated the reproduction of L. wheatleyi and found it to have not only a female-skewed sex ratio but also 5% hermaphrodites.

These freshwater mussels seem to occupy a biogeographically important position between the Western Palearctic mussels of Europe and North Africa and the Introtropical taxa of Southeast Asia. We wish we had more to say. Finding new data on the Middle Eastern mussels would be a great New Year's resolution for 2014.


NSF icon MUSSEL icon
"Making the world a better place, one mollusk at a time."