Mussel of the

Page last updated
5 January 2016

Mussel of the Month

The 2015 Mussels of the Month.

December 2015

NephriticaPronodularia japanensis (Unionidae, Palearctic)

The December 2015 Mussel of the Month is Pronodularia japanensis. Pronodularia is a genus of two species restricted to Japan and Korea in the eastern Palearctic.

When we published our global checklist almost a decade ago (Graf & Cummings, 2007), we didn’t have any mussels classified in the genus Pronodularia. Our current recognition of this genus is based on the work of Takaki Kondo (2008) and his generic revision of the freshwater mussels of Japan.

The story of Pronodularia is a continuation of our serialization of The Tale of Inversidens (and that story is just one part of the epic saga, The Whoa of the Old World Generic Classification of Freshwater Mussels). In many places, our classification of Asian freshwater mussels is very similar to the mid-20th century system of Haas (1969), but this long stasis should not be regarded as evidence that the classification is settled. Rather, it is the result of neglect. But, things are starting to turn around (e.g., Pfeiffer & Graf, 2015). It is the Indotropics that have received the least recent attention, but the Palearctic mussels have seen a fair amount of revision over the last eight years.

The former Inversidens is now split into three genera: Inversidens, Inversiunio, and Pronodularia. As we explained last year at this time, Inversiunio was split from Inversidens to accommodate the fact that some species (like I. reinianus) have the hooked-type glochidia of the family Unioninae, while others have the unhooked-type glochidia of the Gonideinae.* This has happened with other traditional genera once their larvae became better understood (e.g., Lamprotula and Aculamprotula). In our 2007 checklist, we classified Inversiunio among the Unioninae and Inversidens under the Gonideinae.

Way back in 1970, Starobogatov had coined the name Pronodularia for Inversidens japanensis, but no one really took notice. The Soviets had a knack for making up unnecessary new names for mussels. However, Kondo (2008) applied the genus name to distinguish P. japanensis from its former congeners. Why? Good question.

We anticipate that further phylogenetic scrutiny of the Old World mussel genera will uncover and resolve heretofore unknown mussel confusions.

* Actually, we don’t really know any unambiguous morphological synapomorphies that put Inversidens, Pronodularia, and the other genera of the Gonideinae in that subfamily, but the molecules seem to support such a clade (Pfeiffer & Graf, 2015).

November 2015

NephriticaNephritica poeyana (Unionidae, Neotropical)

The November 2015 Mussel of the Month is Nephritca poeyana. Nephritica is a Mesoamerican genus of two species.

As ever, when times are busy we turn to Mesoamerican species for the Mussel of the Month. The less there is to contribute the less we have to write!

So here comes Nephtritica poeyana to save the day. Nephritica is a genus without any distinguishing features except that Frierson (1927) created it without description for N. poeyana and N. haricotti. Haas (1969) followed Frierson's lead, providing a vague shell description but noticing no diagnostic characteristics. Then we (Graf & Cummings, 2007) followed Haas, and here we are now. 5 museum lots, two species barely known from other than the types. Somebody really should work up those Mesoamerican mussels...

October 2015

LepidodesmaLepidodesma languilati (Unionidae, Indotropical)

The October 2015 Mussel of the Month is Lepidodesma languilati. Lepidodesma is a monotypic genus endemic to the Yangtze Basin in China.

With the start of the academic year, no one has time to read (or write) a long, involved Mussel of the Month. It is times like these that we turn to freshwater mussel species about which we know very little. The less is known, the more our ignorance and brevity can be forgiven.

Lepidodesma languilati is one of those mussels. The MUSSEL Project Database provides a string of references that mention this species, but that is just about all they do. The IUCN Red List hit the nail on the head when they tagged this very large bivalve (the shell depicted above is 140 mm long according to Heude, 1874) as "data deficient." In our museum tour of the world and elsewhere, we have only seen 10 lots.

When we did our checklist almost a decade ago, the current consensus was that there were two species in the genus Lepidodesma: L. languilati and L. aligera (Graf & Cummings, 2007). Recently, though, He & Zhuang (2013) sunk the latter into the former, and we have updated our database accordingly. That is it. That's all we know.

September 2015

VenustaconchaVenustaconcha ellipsiformis (Unionidae, Nearctic)

The September 2015 Mussel of the Month is Venustaconcha ellipsiformis. Venustaconcha is a genus of two species found in the Mississippi and Great Lakes drainages of eastern North America.

Venustaconcha ellipsiformis is one of the (at least) 49 species of freshwater mussels that occurs in Wisconsin, USA. The mussels of that state have captured much of our attention this summer, and a milestone in that research was our presentation at the 81st annual meeting of the American Malacological Society at the University of Michigan Biological Station.

Although this project to quantify and describe the patterns of freshwater mussel distributions in Wisconsin has been ongoing for a couple years, the intense activity this summer was motivated by the AMS Great Lakes Malacology Symposium, organized by Dave Zanatta of Central Michigan University. DLG presented a talk entitled, "Biogeography of the freshwater mussels (Unionida: Unionidae & Margaritiferidae) of Wisconsin, USA," co-authored by three former University of Wisconsin-Stevens Point students — Ryan Pappas, Charlie Jordan and Madalyn Zimbric. The two main conclusions from this research are that 1) there is still a lot of work left to do to fully understand freshwater mussel distributions in Wisconsin, and 2) available radiocarbon dates suggest that most species with disjunctions between the Interior and Great Lakes basins arrived after 5000 years before present. This presentation was a triumph of collaboration between the MUSSELp and undergraduate researchers.

On top of all this, MUSSELp alumna Katie Vazquez, recently Ph.D'd by the University of Pennsylvania, won a best student presentation award for her non-mussel-related presentation. And, MUSSELp heir apparent John Pfeiffer of the University of Florida presented his excellent research on Thai freshwater mussels.

The AMS meeting was an outstanding opportunity to share mussel research with our colleagues and for students to get their feet in the malacological door. Hooray!

August 2015

ContradensContradens contradens (Unionidae, Indotropical)

The August 2015 Mussel of the Month is Contradens contradens. Contradens is a genus of six species, widespread in tropical Southeast Asia and the Sunda Islands.

Our current concept of Contradens as a genus largely dates from Haas (1969), and as such, this is a genus hanging low for revision. We suspect that the type species, C. contradens, is “lumped” — that is, that the taxon represents multiple biological/phylogenetic species. Our evidence? Several separate species recognized by Haas (1969) were lumped by Brandt (1974) into a single species, Uniandra contradens,* with multiple geographically isolated subspecies. To you, future gentle-reviser, we offer caution in trying to determine which (Haas or Brandt) was correct. Our guess is that probably neither got it right.

It turns out that Contradens contradens is particularly interesting among freshwater mussels because the species has asymmetrical glochidia. That is, on one larval valve there is a conspicuous marginal appendage (i.e., a hook). If you've never heard of asymmetrical glochidia, it's because they have been largely overlooked. However, they have been described for various SE Asian genera. In a brand new paper by Pfeiffer & Graf (2015), the meager literature on the subject was reviewed, and the authors performed a comprehensive phylogenetic analysis to test the monophyly of the asymmetrical-glochidium-bearing species. The results are somewhat complicated, but the gist is that Contradens is part of a clade of mussels (at least Contradens + Trapezoideus) with asymmetrical glochidia, within the Rectidentinae.

If you are interested in reviewing the history of larval evolution in the Unionidae or examining the most comprehensive phylogeny of the Unionoida to-date, you can download the early online edition of Pfeiffer & Graf (2015) here. This research was done as a part of John Pfeiffer’s graduate work at the University of Alabama. Nice job, John! And, Roll Tide!


* There has been some disagreement as to whether Contradens or Uniandra is the correct name for this genus. The use of Uniandra as senior to Contradens seems to date from Brandt (1974). From where we are sitting, this is just clearly an error. Contradens was first mentioned in the captions to plates 18-22 of Haas (1911) in the Systematisches Conchylien-Cabinet without description. The genus was formally described in a subsequent volume Haas (1913b: 173), but AFTER it was described in Haas (1913a). Uniandra was introduced as a subgenus of Ensidens by Haas (1913b ). From the dates of the Systematisches Conchylien-Cabinet and the Nachrichtsblatt der Deutschen Malakozoologischen Gesellschaft, it is clear that Haas (1913a) was published before (1913b), and thus Contradens has priority.** In fact, it would seem that Haas’s (1911) figure captions satisfy ICZN Article 12.2.5, and the name Contradens would be available from that date.

** Even if one (somehow) wasn’t satisfied with these dates and insisted that both Contradens and Uniandra date from the same work, Modell (1964), acting as First Reviser (ICZN Art. 24.2), recognized Contradens as the senior synonym. Starobogatov (1970) also considered Uniandra junior to Contradens.

July 2015

ActinonaiasActinonaias sapotalensis (Unionidae, Neotropical)

The July 2015 Mussel of the Month is Actinonaias sapotalensis. Actinonaias is a genus of seven species endemic to Mexico.

It may come as a surprise that the freshwater mussel genus Actinonaias is actually restricted to Central America. After all, there are two species, “A.” ligamentina and “A.” pectorosa, that are well known in the eastern part of the United States. What the mucket is up with that? The short answer is that we now classify those two North American species in the genus Ortmanniana, and you can look at the taxonomy in our database (and elsewhere on this web site) or on the ITIS web site. Some longer answers follow.

How did we get a classification that lumped seven Central American species and two Mississippi Basin species into the genus Actinonaias?

Back at the dawn of the modern era of mussel classification, Simpson (1900) classified A. sapotalensis, A. medellina, and A. computata (Mesoamerican) in the genus Nephronaias, and he listed “A.” ligamentina (+ carinata) and “A.” pectorosa (+ perdix) (Nearctic) in the genus Lampsilis. When Ortmann (1912) examined the anatomy of A. sapotalensis, “A.” ligamentina, and “A.” pectorosa, he decided that the latter two species were morphologically distinct from the genus Lampsilis, but they were similar to A. sapotalensis. Indeed, as far as Ortmann was concerned about the soft parts, all three of these species were pretty similar to Obovaria. In order to update Simpson (1900), Ortmann (1912) moved “A”. ligamentina and “A.” pectorosa out of Lampsilis and into Nephronaias with A. sapotalensis.

Soon afterward and with more data, Frierson (1917) pointed out that other species of Nephronaias (such as the type species, N. plicatula) were anatomically more similar to genera like Elliptio and Pleurobema. According to Frierson, Nephronaias was thus composed of Elliptio-like species (elongate non-dimorphic shells with dark periostracum, ectobranchus) and Lampsilis-like species (sexually dimorphic shells with green rays, marsupium restricted to part of outer demibranchs). To correct this obviously confusing situation, Frierson (1917) applied Actinonaias to the lampsiline species like A. sapotalensis, A. medellina, and A. computata. It was Ortmann & Walker (1922) that decided that if A. sapotalensis was to be moved from Nephronaias to Actinonaias, so should “A.” ligamentina and “A.” pectorosa.

Besides the fact that there are several species of Actinonaias of questionable validity, no phylogenetic analysis has ever tested the monophyly (or non-monophyly) of the species formerly classified as Actinonaias. However, the biogeography of the two groups of species (Actinonaias sapotalensis, etc. vs. “A.” ligamentina and “A.” pectorsa) represents an unprecedented disjunction between the Mesoamerican and Nearctic faunal provinces. Separating the latter two species into Ortmanniana and leaving Actinonaias to A. sapotalensis and other Central American species makes biogeographical sense. The question that needs a phylogenetic answer is: Does A. sapotalensis share a more recent common ancestor with Ortmanniana ligamentina or other Mexican species? We hypothesize that our July 2015 Mussel of the Month belongs to a clade of Central American lampsilines.

Why did a classification that lumped seven Central American species and two Mississippi Basin species into the genus Actinonaias last as long as it did?

Very few researchers were ever confused by this classification because after Frierson (1917), very few researchers ever worried about Central American freshwater mussels. That is, for all intents and purposes, Actinonaias consisted of only two species of interest: “A.” ligamentina and “A.” pectorosa.

We should say “for MOST intents and purposes” because Frierson (1927) and Haas (1969) recognized that Ortmanniana in the Mississippi Basin was distinct from Actinonaias in Mexico. And, Watters et al. (2009) indicated the same thing. We imagine it is easy for systematists to get on board with the idea of splitting up the old Actinonaias. The sticking point is likely the required name change: Actinonaias stays with its type species, A. sapotalensis. The persistence of the use of Actinonaias for the species now in Ortmanniana has been a case of letting sleeping dogs lie.

We previously left these sleeping dogs to lie there in their likely paraphyly (Graf & Cummings, 2007), but no more. We have updated our classification to reflect the removal of Ortmanniana from Actinonaias. The MUSSEL Project Database has recently been incorporated into the Integrated Taxonomic Information System (ITIS), and the change is reflected there. Here’s to progress!

June 2015

GrandidieriaGrandidieria burtoni (Unionidae, Afrotropical)

The June 2015 Mussel of the Month is Grandidieria burtoni. Grandidieria is a monotypic genus endemic to Lake Tanganyika in Central Africa.

Grandidieria burtoni is such an interesting little African mussel that we are frankly surprised it as taken us so long to give it a spot as the Mussel of the Month. This unionid first came to our attention during DLG's dissertation work to investigate the phylogeny of freshwater mussel families. Anatomically, these bivalves belong to the family Unionidae — they have pseudocardinal and lateral hinge teeth, a supra-anal aperature, and small labial palps (Bloomer, 1933). As importantly, G. burtoni lacks the diagnostic characters of the Iridinidae (the other family found in Lake Tanganyika), such as a deep ligamental sinus, large pedal protractor scars, etc. However, G. burtoni broods its glochidia (a unionid trait) in its inner demibranchs (an iridinid trait) (Graf, 2000; Graf & Cummings, 2006). We still haven't sorted that out.

Our affection for Grandidieria burtoni is also related to our long-time admiration of its name-sake, the polyglot explorer Richard Francis Burton. Back in 2004, during our collections work in London, we visited Burton's tomb, and we also had the opportunity to examine the type specimen collected by Burton and John Hanning Speke on their trip to Lake Tanganyika.

Another feature that distinguishes Grandidieria burtoni from other African mussels is that it is so well represented in malacology collections. A few years back, we published a study of African freshwater mussel biogeography based on museum specimens (Graf & Cummings, 2011). Despite the fact that G. burtoni is endemic to Lake Tanganyika, it is the 2nd most common species in collections (486 lots) — behind only Coelatura aegyptiaca (578) and ahead of the much more widespread Etheria elliptica (454). Despite the observation that there are 76 other Afrotropical species of freshwater mussels, these three species account for more than 25% of all the museum lots. This may seem paradoxical given the relatively small area of occurrence of G. burtoni. However, it turns out that the drawers and drawers of large lots of Grandidieria are largely flotsam ("rebut"). Tanganyika is (relatively) well-studied, and G. burtoni shells apparently wash up in piles.

Recently, our work on the biogeography of the freshwater mussels (Graf & Cummings, 2011) was added to the Global Freshwater Biodiversity Atlas. That site has interactive maps showing the patterns of species richness in Palearctic and Afrotropical Africa as well as Madagascar. We are grateful to Pablo Tedesco for inviting our submission.

May 2015

AneminaAnemina fluminea (Unionidae, Palearctic)

The May 2015 Mussel of the Month is Anemina fluminea.Anemina is a genus of five species found in eastern Asia.

We chose Anemina fluminea as the Mussel of the Month for May because it is emblematic of the challenges that still exist in freshwater mussel taxonomy and systematics. The upshot is that we know of very little science that would allow us to answer the question, "Upon what characteristics (synapomorphies) is Anemina based?" Anemina is a hypothesis about the evolutionary relationships of the five species in the genus. What is the evidence that supports that hypothesis? The short answer: it is pretty slim.

Until only about a decade ago, there was only a single species in the genus Anemina: A. arcaeformis, the type species. Lindholm (1925) created the genus Haasiella for Anodon arcaeformis Heude 1877 because the species was reported to lack the larval thread and hooked margin found in typical anodontine glochidia. However, Haasiella was preoccupied by a genus of myriapod, so Haas (1969) provided a replacement name, the subgenus Anemina — Anodonta (Anemina) arcaeformis.

Then, out of the blue, Prozorova et al. (2005) put four additional species in Anemina: A. euscaphys, A. globosula, A. angula, and (our Mussel of the Month) A. fluminea. This was a bit of a shift in taxonomy since these four species had previously been either synonymized with Sinanodonta woodiana, omitted, or were unknown to Haas (1969). Is it reasonable to assume that these mussels also have the larval characteristics of A. arcaeformis? If so, it is certainly worth noting that Prozorova et al. (2005) placed the type of Anemina in a different genus: Buldowskia arcaeformis.

This is where we enter the story (Graf & Cummings, 2007). In trying to sort of the global freshwater mussel species diversity, we simply followed Prozorova et al. (2005) in classifying the other four species in Anemina, and we included A. arcaeformis because the rules of nomenclature required it. If there is an Anemina, then A. arcaeformis is one. Our treatment of Anemina was subsequently applied by Bogan (2010) and then mostly copied verbatim from a previous iteration of this web site by He & Zhuang (2013).

So, this is where we are at. A. fluminea resides in Anemina because Prozorova et al. (2005) put it there. However, those authors didn't classify the type of Anemina in Anemina, so their taxonomy is suspect. One could put the blame on us for floating the current concept of Anemina, but since subsequent authors have not attributed their taxonomy to us, perhaps we can take their use of the name as confirmation rather merely following. For now, we will keep Anemina.

April 2015

PhysunioPhysunio superbus (Unionidae, Indotropical)

The April 2015 Mussel of the Month is Physunio superbus. Physunio is a genus of nine species reported from India and Burma to the Mekong Basin and the Sunda Islands.

Physunio superbus is the April 2015 Mussel of the Month. And, for good reasons: we haven't honored Physunio before, and we need to update this website. It is a perfectly nice looking shell from a respectable species. But, we don't really have anything else to say about it.

The real honoree this month is MUSSELp co-founder Kevin Cummings, to whom the Freshwater Mollusk Conservation Society bestowed the Lifetime Achievement Award. From 22-26 March 2015, Kevin visited St. Charles, Missouri to attend the biennial symposium of the FMCS. He gave a presentation on the latest MUSSELp endeavor, "The Freshwater Mussels (Bivalvia: Unionoida) the rio Amazon Drainage With an emphasis on the Rio Xingu basin, Brazil." (A previous run at this topic was presented at the annual meeting of Illinois Chapter of the American Fisheries Society.) At the FMCS banquet, KSC was presented with a plaque to commemorate his years of service to the causes of freshwater mollusk research and conservation. DLG wrote a letter in support of Kevin's nomination for this award, which read in part:

"Kevin’s career (so far) has been a rising tide that has floated all of our malacological boats. Future generations of scientists and students working in the fields of freshwater biodiversity and conservation will remember Kevin Cummings as one of the Bright Lights of the renaissance in freshwater molluscan research of the last few decades..."

Congratulations to Kevin!

March 2015

AlathyriaAlathyria jacksoni (Hyriidae, Australasian)

The March 2015 Mussel of the Month is Alathyria jacksoni. Alathyria is a genus of four species endemic to Australia.

Alathyria jacksoni is the type species of the genus Alathyria, and from where we are sitting, it may be the only species that is really in that genus.

On this web site right now, we follow McMichael & Hiscock (1958), who largely followed Iredale (1934, 1943) in recognizing 4 species in Alathyria: A. jacksoni, A. pertexta, A. condola, and A. profuga. It is really interesting that Iredale's classification has held up for so long, since he was an F.C.-Baker-esque splitter who never found variation that didn't merit a new taxon. But Iredale, and later McMichael & Hiscock, grouped these taxa together because of their large size. These are the big Australian mussels.

But after 50 years or so, the addition of DNA into the analytical mix has demonstrated that this classification isn't natural. That is, it doesn't reflect evolutionary history. Back in 2004, Andrew Baker et al. discovered that A. jacksoni was nested within the genus Velesunio. That was the only Alathyria species they considered, but their result indicated some confusion regarding the genus-level taxonomy of the Velesunioninae.

Graf et al. (2015) have just published a new paper that puts another nail in the coffin of the traditional view of Alathyria. Their analysis included three species of Alathyria, A. jacksoni among them, and all three were found to be more closely related to species of other genera. There is still some work to do on the taxonomy and classification of Australia's freshwater mussels. When that revisionary work gets completed by the locals in Oz (hopefully taking advantage of all the specimen records we have made available on this site), we will update our classification.

Perhaps the neophyte to the field of systematics will draw from this outcome the conclusion that no predictive classification can be achieved without molecular data. But it isn't only the data that differ between the classical work of McMichael & Hiscock (1958) and the Earth-shatteringly rigorous modern analysis of Graf et al. (2015). We would instead emphasize the supremacy of repeatable cladistic methods to traditional authoritarian "Just So" stories.

February 2015

AcostaeaAcostaea rivolii (Etheriidae, Neotropical)

The February 2015 Mussel of the Month is Acostaea rivolii. Acostaea is a monotypic genus, endemic to the Rio Madgalena, Colombia, South America.

Acostaea is one of four monotypic genera currently classified in the family Etheriidae. The other three are Etheria, Pseudomulleria, and Bartlettia. A good common name for the etheriids might be "freshwater oysters." Although traditionally, the composition of the Etheriidae was unproblematic, modern cladistic analyses have recovered conflicting results.

Etheria (from Africa & Madagascar) is mostly unproblematic. It is the type genus of the Etheriidae. If there is an Etheriidae, Etheria will be classified in it. Bartlettia is kind of problem that we addressed in a previous MotM. The real existential problems for the Etheriidae are Acostaea (from South America) and Pseudomulleria (from India). The available molecular data rendered the family both paraphyletic and polyphyletic (Bogan & Hoeh, 2000; Hoeh et al., 2009). Acostaea was recovered as sister to the Mycetopodidae, and Etheria was sister to that clade (paraphyletic). Pseudomulleria, on the other hand, was placed in the Family Unionidae (polyphyletic). However, cladistic analysis using morphological characters found that the monomyarian Acostaea and Pseudomulleria were sister to each other, and dimyarian Etheria was sister to that pair (Graf & Cummings, 2006, 2010). In either case, there are interesting biogeographical consequences for these species widely disjunct on the former fragments of Gondwana.

We are as geeked up as anybody about the new phylogenetic data that have become available over the last couple decades — especially from molecular characters. However, this issue with the Etheriidae remains a problem that awaits more data to resolve.

January 2015

ToxolasmaToxolasma lividum (Unionidae, Nearctic)

The January 2015 Mussel of the Month is Toxolasma lividum. Toxolasma is a genus of eight species found in eastern North America, from the Great Lakes south to the Gulf of Mexico.

The freshwater mussel genus Toxolasma is distinctive for its small adult size — generally less than an inch. At that size, the shells are fully sexually dimorphic in the typical lampsiline style. Good, interesting stuff.

Toxolasma lividum does not occur in Wisconsin, but T. parvus does. In fact, T. parvus was described from the Dairy State. Recent UWSP graduate Charlie Jordan had been working on the distributions of freshwater mussels like Toxolasma parvus in Wisconsin. Last spring, he and Madalyn Zimbric (now at the University of Michigan) presented a poster on patterns of freshwater mussel species richness in Wisconsin at the UWSP College of Letters and Sciences Undergraduate Research Symposium. Their poster, "A Biodiversity Informatics Assessment of Wisconsin Freshwater Mussels" will form the basis of a future publication on the subject.

And, speaking of the freshwater mussels of the North America, it seems that we have a new book chapter. Our previous bivalve chapter from Thorp & Covich's invertebrate zoology book (Cummings & Graf, 2009) has been recycled into Thorp & Covich's general freshwater invertebrates book (Cummings & Graf, 2014). We were surprised, too.


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