Mussel of the

Page last updated
6 January 2019

Mussel of the Month

The 2018 Mussels of the Month.

December 2018

Anodonta anatinaAnodonta anatina (Unionidae, Palearctic)

The December 2018 Mussel of the Month is Anodonta anatina. Anodonta is composed of 12 species: six from the western Palearctic region (Europe, north Africa, and Middle East) and six from western North America and Mexico.*

The freshwater mussel world has gotten a little more harmonious. This Mussel of the Month post is about the people of the world unifying under a single vision (more or less) for freshwater mussel classification. What we are talking about is an ending for the Soviet Comparatory species concept in favor of species as evolutionary entities.

We all know that freshwater mussels are a challenge for the uninitiated to identify due to high intraspecific shell variation and the lack of meristic characteristics. Keys are not that helpful except in localized geographical areas and are seldom constructed unless forced by editors (e.g., Cummings & Graf, 2009). This subjective deference to authority has created a couple movements over the centuries to make species identification more "objective" using shell measurements. One of these was the French Nouvelle École of Bouguignat, Locard, and others. In the last quarter of the 1800’s they had the idea that mollusk species could be recognized by making lots of measurements and defining species as shells differing from others by some arbitrary set of dimensions. Unfortunately, the bar for distinctiveness was set very low, and one of the dimensions was absolute length — so just being a different size at the time of measurement contributed to taxonomic splitting. And split they did! Instead of around a dozen French species, Arnould Locard recognized more than 300. Most of these were ignored by Simpson (1900) in his assessment of global mussel diversity because, in his words, “life is too short.” The Nouvelle École was closed, and the species and (especially) genera they concocted remained in the unsettled taxonomic ether until Graf (2010, 2011) put the final nails in their coffins.

The 20th century (and later) effects of all this 19th century splitting were eventually sorted out, but it has taken a while. In our global checklist (Graf & Cummings, 2007), we followed Haas (1969) by placing Anodonta anatina as a junior synonym of A. cygnea. There were plenty of references at the time recognizing A. anatina and A. cygnea as distinct, but those works did not unambiguously account for all the synonymous nominal species (more that 550 of them between the two). Haas did, and since accounting for synonymy was part of our goal, his species circumscription won out.

More recently, the corpse of the Nouvelle École had been resurrected by Starobogatov and other malacologists of the former Soviet Union (Shikov & Zatravkin, 1991). They used a single characteristic, the curve of the profile of a valve, to distinguish species. This was known as the Comparatory Method, and, as would be expected, it led to a proliferation of new species and genera. As a rule of thumb, Comparatory genera are largely equivalent to Western species (Korniushin, 1998; Kantor et al., 2010). DLG dealt with those taxa in a separate paper (Graf, 2007) so they wouldn’t gum up our checklist (Graf & Cummings, 2007).

The Comparatory School of Malacology persisted in parallel with the Western system into the Cladistic Era (Startobogatov et al., 2004). As we discussed back in November 2013, some Russian scientists, like Ivan Bolotov et al. (2013), have been disrupting the practice of equating shell curvatures with freshwater mussel species, but others, like Victor Bogatov (2013), continued to argue in favor of the old ways.

But recently, there have been two papers applying molecular characters to Russian freshwater mussels that have convincingly demonstrated that, at least for Anodonta anatina, mussels with slightly different shell shapes belong to the same biological populations (Klishko et al., 2018; Bogatov et al., 2018). Perhaps that comes as little suprise. It is significant (to us, anyway) that Bogatov — who described 40 Comparatory species and 5 genera since 1987 — was the lead author on one of those articles. We hope this begins a global reconciliation of freshwater mussel taxonomy.

As our friend, Yuri Kantor, pointed out to us, a shift in taxonomy in Russia can have consequences for mussel conservation. The Red Data Book of the Russian Federation is a national counterpart to the Red List produced by the International Union for the Conservation of Nature. Widespread abandonment of split Comparatory species for lumped biological species could result in freshwater mussel populations bureaucratically shifting from one conservation status to another and sowing confusion for the people that study and manage those mollusks.** But perhaps some extra paperwork is worth taxonomic détente.

* Obviously, the distribution of Anodonta is interesting — in the sense that it makes no biogeographical sense. It is the among last remnants of the 19th century system wherein all known mussels we basically classified as either Unio, Anodonta, or Margaritifera. Since Simpson (1900), those unwieldy, unnatural genera have been whittled down as new genera were described/recognized. The type species of Anodont is A. cygnea, so Anodonta sensu strico is certainly part of the European fauna. "Anodonta" has finally been scrubbed from eastern North American mussel fauna and replaced by Pyganodon, Utterbackia, and Utterbackiana, but you don't need too be too gray to remember when Anodonta grandis, A. imbecillis, and A. suborbiculata were all in common usage. The taxonomy of western American anodontas remains to be modernized.

** Yuri has also pointed out that in the latest (as yet unapproved) Red Book, the Comparatory Species have already been removed.

November 2018

Coelatura cridlandiCoelatura cridlandi (Unionidae, Afrotropical)

The November 2018 Mussel of the Month is Coelatura cridlandi. Coelatura is a genus of 22 species known only from sub-Saharan Africa and the Nile.

There are a couple good reasons one might highlight C. cridlandi as the Mussel of the Month. We have previously featured two other species of Coelatura (C. aegyptica and C. lobensis). However, the genus isn't monophyletic (Graf et al., 2014). Since the various lineages, after they have been studied in more detail, may be split among various available names (e.g., Zairia), C. cridlandi might anticipate further increases in freshwater mussel genera (as we documented earlier this year). That would be as good of a reason as any to shine a spotlight on this species.

But we chose C. cridlandi this month because it is one of only 51 freshwater mussel species described during the 20 years from 1940-1960. Of those, 29 were described as species (i.e., not subspecies), and only 10 are still regarded as valid. In the preceding 20 years, 268 new species and subspecies were named, with 50 still valid, while in the subsequent two decades, 67 were described and 21 are valid. Even with the general trend of fewer new species-group level taxa being described (in the 1st decades of the 20th century, there were 585 and 1449 before that), the lull from 1940-1960 is noticeable.

We discovered this pattern while investigating the history of publications and the use of freshwater mussel names over the last 260 years. The chart shows the number of publications and "taxonomic opinions" that relate to Recent freshwater mussel species by decade in the MUSSEL Project Database. “Publications” refers to sources of information about freshwater mussels like articles, books, parts of serial volumes, and even some web sites like WoRMS and the IUCN Red List. “Taxonomic opinions” are the citations of species names — whether valid or as synonyms. At this moment, we have a total of 2066 publications and 68,648 taxonomic opinions relating to Recent freshwater mussels, and these data, as well as specimen records, form the basis of the MUSSELpdb. We obviously haven't captured every publication and every use of a mussel name since Linnaeus, but we perhaps do have a big enough sample to see meaningful trends.

When it comes to taxonomic opinions, several high peaks are evident for certain decades, and these correspond to comprehensive global treatments of mussel diversity that provided extensive synonymies (e.g., Simpson, 1900, 1914; Haas, 1969) — lots of opinions. Also evident is the trough during the 1940's and 1950's: the post war years. Malacologists were still doing some work, but their rate definitely slowed while people were distracted rebuilding the world. Local work was going on, like Mandahl-Barth (1954) in Lake Victoria describing C. cridlandi, but between Simpson (1914) and Haas (1969) no one was on the beat of global freshwater mussel species diversity. And, after Haas (1969) the next global treatment was our own (Graf & Cummings, 2007).

At this moment, we are in an exponential explosion of publications and taxonomic opinions that correspond to the arrival in the 1990’s of the Internet and phylogenetic studies of freshwater mussels. (Presumably, our dataset has some bias towards the most recent decades, too).

These data are served to you, gentle-reader, in the MUSSELpdb on this web site. For example, for any nominal species, the whole “taxonomic history” of opinions is provided. Click here to see an example for Coelatura cridlandi. The “taxonomic opinions” associated with each publication are also available, such as Graf & Cummings (2007).

October 2018

PaetulunioPaetulunio fabalis (Unionidae, Nearctic)

The October 2018 Mussel of the Month is Paetulunio fabalis. Paetulunio is a monotypic genus endemic to eastern North America.

P. fabalis is the sole species of Paetulunio, another new genus recycled by Watters (2018) from the broken remains of Villosa. So, far we have already covered Leaunio, and we still have Cambarunio and Sagittunio to go. Generic revisions have kept us busy this year.

Since the beginning of the Universe, there have only been a handful of studies that provided hard phylogenetic evidence for the evolutionary relationships of P. fabalis. Ortmann's (1912) anatomical authority was the basis for the pre-2018 concept of Villosa. He called them all Micromya. Among published works, there have been various representatives of the old Villosa included in phylogenetic analyses. But, we know of only three published works that included P. fabalis with at least one other former genus-mate: Zanatta & Murphy (2006), Inoue et al. (2013), and Lane et al. (2016).* The most comprehensive analysis is the “unpublished” (but widely internet available) dissertation of Kuehnl (2009). Across the board, the upshot is fairly consistent: P. fabalis has been found to share a more recent common ancestor with various other mussels than any of the old Villosas. So, it is currently treated as its own monotypic genus.

The type species of Micromya is Unio lapillus Say, 1831, which has been regarded as a junior synonym of P. fabalis for more than 100 years. However, Micromya is preoccupied by an older use of the name for some wood midges.

* Lane et al. (2016) was not sufficiently rooted to actually provide a test the relationships of P. fabalis to the other species of Villosa sensu lato.

September 2018

IndochinellaIndochinella pugio (Unionidae, Indotropical)

The September 2018 Mussel of the Month is Indochinella pugio. Indochinella is a monotypic genus from the Irrawaddy and Salween rivers of Myanmar.

Indochinella is a new genus described just this year, and I. pugio is a player in the recent revolution of new genera and family-group level taxa that have erupted onto the scene over the last couple years. The story of Indochinella actually starts with the genus Oxynaia.

Oxynaia was introduced by Haas back in 1911 in the captions to three plates — just pictures and names. An actual description and type designation followed two years later — Haas’s contributions to Systematisches Conchylien-Cabinet von Martini und Chemnitz coming in installments. The original plate captions included other species in Oxynaia that by 1913 were transferred to Ensidens in revised plate captions. This story is already off to a complicated start.

There is little to say about Oxynaia over the subsequent 100 or so years. During that period the genus came to house 5 species: O. jourdyi (the type species), O. micheloti, O. diespiter, and O. gladiator from northern Vietnam, and O. pugio from Myanmar. Oxynaia got classified, of course, in various summaries of freshwater mussel taxonomy, but in the pre-cladistic era, everyone was just guessing and flinging their authority around. In 2007, when we did our global checklist, we had enough information to know that we didn’t know where Oxynaia should go. From the anatomy the genus was clearly representative of the family Unionidae but otherwise incertae sedis (Graf & Cummings, 2006, 2007).

In 2010, Bieler et al. proposed a bold classification of the Bivalvia including the Unionoida (or Unionida — that’s where that alternative spelling originated) down to the tribe level. No new data or phylogenetic analyses had become available since we decided we didn’t know enough to precisely classify Oxynaia three years earlier, and Bieler et al. (2010) for some reason located the tribe Oxynaiini among the North American Ambleminae (with a question mark). There was a lot that was novel in the Bieler et al. classification, and that classification provided a more reasonable starting place for the phylogenetic work that would follow than did the clearly flawed arrangements proposed by Modell (1964), Haas (1969), Starobogatov (1970), and others.

The first phylogenetic study to incorporate Oxynaia was Whelan et al. (2011). Perhaps unsurprisingly, O. pugio from Myanmar was not found to be a member of the Ambleminae. Instead, the tribe Oxynaiini (represented by O. pugio) was discovered to be a lineage of the subfamily Parreysiinae, along with other genera from southern Asia and Africa. Based on that study, we updated the classification of freshwater mussel subfamilies, moved the five species of the genus Oxynaia to the Parreysiinae, and wrote about Oxynaia as Mussel of the Month.

But this year, the heretofore untested monophyly of Oxynaia threw a wrench into the works. Bolotov et al. (2018) demonstrated that while indeed O. pugio of Myanmar belongs to the Parryesiinae, the type of the genus, O. jourdyi, and the other three species from Vietnam really belong with the genus Nodularia in the subfamily Unioninae. Oxynaia became a junior synonym of Nodularia, and O. pugio was left without a genus. Bolotov et al. (2018) gave us the name Indochinella for I. pugio and the tribe formerly called the Oxynaiini became the Indochinellini.

Further advances to the classification of southern and southeast Asian mussels have precipitated from a follow-up article by Pfeiffer et al. (2018) wherein Scabies, Harmandia, and Unionetta finally found a tribe in the Indochinellini. That research expanded our understanding of the taxonomic and geographic extent of the Parreysiinae from the Indus east to the Mekong River.

So many fuzzy areas of freshwater mussel phylogeny are coming into focus!

August 2018

PseudodontoideusPseudodontoideus connasaugaensis (Unionidae, Nearctic)

The August 2018 Mussel of the Month is Pseudodontoideus connasaugaensis.* Pseudodontoideus is a genus of two species from the Gulf Coastal Plain of North America.

This year we have been kept busy with the splitting of freshwater mussel genera. Pseudodon has been broken into three genera, Villosa is now spread among six genera, and Sinohyriopsis has been split from Hyriopsis. As we explained when the new genus Leaunio was Mussel of the Month, we are seeing generic revisions unlike anything in our more than 15-year history.** There are even more changes coming down the pipe that we will have ready on this web site for next month (along with a necessary update to the MUSSELpdb).

Thanks to Smith et al. (2018), we have another instance of traditional genus disruption. This time it is Strophitus that is split. S. undulatus stays put, but P. connasaugaensis and P. subvexus belong in a separate lineage called Pseudodontoideus. But as Strophitus lost two species, it gained three. S. radiatus (formerly of Anodontoides) was divided into multiple species along the Gulf Coastal drainages of North America. These genera have been fairly stable in their taxonomy until recently (Frierson, 1927; Haas, 1969; Burch, 1975; Graf & Cummings, 2007; Williams et al., 2017), but again it hasbeen shown that as we tug at the loose strings, our tidy classification of freshwater mussel tends to unravel.

It is a good thing that we already have a good database structure to keep track of all these thrilling changes in freshwater mussel taxonomy!

* Pseudodontoideus connasaugaensis (32 characters) is the longest freshwater mussel name — even longer than Prisodontopsis aviculaeformis (29).

** The MUSSEL Project Web Site was launched October 2002, we have been serving taxonomic data on freshwater mussels since December of the same year, and in August 2003 we designated our first Mussel of the Month.

July 2018

PseudodonPseudodon inoscularis (Unionidae, Indotropical & Palearctic)

The July 2018 Mussel of the Month is Pseudodon inoscularis. Pseudodon is a widespread genus of 16 species extending from Japan to Indochina, Myanmar, and the Sunda Islands.

We have been putting off dealing with Pseudodon as MotM for more than a decade because even though it is a well-known and species-rich genus, the taxonomy has been a mess. When we did our global checklist (Graf & Cummings, 2007), it was evident from the number of subgenera employed by Haas (1969) that there was a lot of phylogenetic diversity that needed to be accounted for. At the same time, Brandt (1974), in his comprehensive treatment of Thai mussels, had proposed a novel classification.

Since then there has been a good deal of phylogenetic work* (e.g., Pfeiffer & Graf, 2015, Bolotov et al., 2017) and Pseudodon sensu lato has so far been divided among three genera: Pseudodon s.s. (16 spp.), Bineurus (5) and Monodontina (4). This table shows the classifications used in the few publications needed to get a handle on the relevant taxonomy: Zieritz et al. (2018), Bolotov et al. (2017), Graf & Cummings (2007), Brandt (1974), Haas (1969), and Simpson (1914). These works provide a reasonable overview of more than a century of malacology.

The splitting of Pseudodon s.l. into three genera follows Bolotov et al. (2017), but that phylogenetic analysis did not consider several of the former subgenera: Chrysopseudodon, Cosmopseudodon, Diplopseudodon, Nasus, and Obovalis. For the time being, we have left those as part of Pseudodon s.s., but we won’t be surprised when more splitting is necessary.

The other thing that is evident from our alignment of Pseudodon s.l. classifications is that, with the exception of Brandt’s (1974) cross-genus over-lumping, the species-level circumscriptions have been relatively stable since Simpson (1914).

* “a good deal of” = “more than none”

June 2018

LeaunioLeaunio lienosus (Unionidae, Nearctic)

The June 2018 Mussel of the Month is Leaunio lienosus. Leaunio is a newly recognized genus of five species endemic to eastern North America

Back in April with Villosa, we talked about some of the new genera introduced by Watters (2018). Leaunio is one of those new taxa. In fact, (with some qualification) the last two years have been a modern explosion of new freshwater mussel genera.

Since we kicked off the MUSSEL Project in 2003, 10 new freshwater mussel genera have been described. Fully of 10% of those were described by us (Germainaia), and 70% have been described since 2017.

In the big picture (click here to see the graph), this latest flurry of genus-group level activity is a minor blip. During the 19th and early 20th century, there were multiple booms of genus-creating, some attributable to particular authors and works — for example, Rafinesque (1820, 1831), Swainson (1840), Bourguignat (1880-1881), Locard (1889, 1890), Servain (1890), Fischer & Crosse (1894), Simpson (1900), Frierson (1927). Other authors like Fritz Haas trickled their genera out across multiple years.

The colors reflect how many genera described in a particular year are currently treated as valid (green) and how many are regarded to be synonyms (gold).

In addition to describing new genera, we (as in the freshwater mussel systematics community) have been resurrecting genera that had been synonymized. A decade ago, Graf & Cummings (2007) recognized 165 valid freshwater mussel genera. Today: 177! What a time to be alive.

May 2018

MycetopodellaMycetopodella falcata (Mycetopodidae, Neotropical)

The May 2018 Mussel of the Month is Mycetopodella falcata. Mycetopodella is a monotypic genus found in the upper Amazon and Orinoco basins of northern South America.

We don’t have much to say about Mycetopodella. It has been nearly universally recognized as monotypic (i.e., M. falcata), in the same subfamily with the genus Mycetopoda (Parodiz & Bonetto, 1963; Graf & Cummings, 2007; Pereira et al., 2014). Haas (1916) described a single synonym based on a single specimen (M. boliveri), but no one seems to have been confused by it.

However, this widespread agreement over the last century resulted largely from a lack of contrary opinions rather than any kind of assent based on convincing evidence. Marshall (1927) described the genus as distinct from Mycetopoda largely to highlight the similarity of M. falcata with Solenaia of southeast Asia. It has never been included in a phylogenetic analysis (that we know of).

April 2018

VillosaVillosa villosa (Unionidae, Nearctic)

The April 2018 Mussel of the Month is Villosa villosa. Villosa is a genus of four species endemic to southeastern North America.

That isn’t a typo — Villosa, as we currently recognize the genus, has only four species. Until we updated our database of over spring break, Villosa had 15 species (Williams et al., 2017). But then Tom Watters (2018) revised the classification of those taxa (and others) and wound up with seven genera where we previously had three (including Ligumia and Venustaconcha).

We have been waiting for some time to feature Villosa as the Mussel of the Month. Kody Kuehnl’s (2009) dissertation of the phylogenetic relationships of Villosa sensu lato has been on our radar for years, and that work forms the basis of this revision.

The revision of Villosa as well as a few other works recently incorporated into the MUSSEL Project database (e.g., Froufe et al., 2017; Zieritz et al., 2018; Smith et al., 2018) added 17 new species to our global tally. Those changes are reflected in the latest versions of the MUSSELpdb and the Unionoida cum Grano Salis pages.

March 2018

TritogoniaTritogonia verrucosa (Unionidae, Nearctic)

The March 2018 Mussel of the Month is Tritogonia verrucosa. Tritogonia is a monotypic genus found in the eastern United States.

Tritogonia verrucosa as the Mussel of the Month ends a long-running discussion we have had on this web site regarding how to revise the genus-level classification of the species formerly classified under the genus Quadrula sensu lato.

Back in the day (e.g., Williams et al., 1993), there were there three genera in this story: Quadrula (several spp.), Cyclonaias (1 sp.), and Tritogonia (1 sp.). But in 2003, it was discovered that T. verrucosa was actually nested within a clade otherwise composed of Quadrula s.l. species (Serb et al., 2003). One way to solve this problem of “taxonomic-load” was by simply classifying T. verrucosa as a species of Quadrula s.l. (Willams et al., 2008).

In our global checklist (Graf & Cummings, 2007), we went another direction. Serb et al. (2003) had recovered clades of the traditional subgenera used to divide up Quadrula s.l. Rather than omitting all that phylogenetic information from the genus-level classification, we simply elevated the long recognized (e.g., Frierson, 1927; Thiele, 1934) subgenera to genera: Quadrula s.s., (type: Q. quadrula), Amphinaias (type: A. couchiana), and Theliderma (type: T. metanevra). This left Tritogonia intact as a monotypic genus.

Our checklist revision wasn’t perfect. Since we were endeavoring to base our taxonomy on the published record and not make novel revisions, we followed Frierson (1927), Haas (1969), and others to circumscribe species into genera. Unio couchianus Lea, 1860 was considered by those authors to be in the same genus as what had been known as Quadrula pustulosa, so the Pustulosa-group became Amphinaias. However, in reality, Q. couchiana seems to be affiliated with Q. quadrula (although no phylogenetic work has been done). The genus-level names Pustulosa and Bullata are available for that group of species.

But then there was a new wrinkle. Campbell & Lydeard (2012) and others showed that the monotypic Cyclonaias belongs among the Pustulosa-group, and reclassification of C. tuberculata to the old Amphinaias secured the name Cyclonaias for the whole clade.

Recently, the four-genus system — Quadrula, s.s., Cyclonaias, Theliderma, and Tritogonia — was codified by Williams et al. (2017), and we have updated the classification on this web site. Now we just need to solve the problem of Uniomerus being a quadrula...

February 2018

MicrodontiaMicrodontia anodontaeformis (Hyriidae, Australasian)

The February 2018 Mussel of the Month is Microdontia anodontaeformis. Microdontia is a monotypic genus endemic to New Guinea.

Microdontia anodontaeformis is another one of those freshwater mussels about which we know almost nothing. Google it, and the top hits are on this web site. That usually indicates to us that there isn't too much more information out there than we are already serving. Unless, of course, you search only with the genus name. Then you get lots of dental web sites about small teeth but not freshwater mussels.

In addition to believing that M. anodontaeformis exists, it does its existing on the Australasian island of New Guinea, and it is classified in the Velesunioninae with some Australian hyriids. That is about the extent of our knowledge.

We are busy this month, so we will leave it at that.

January 2018

SinohyriopsisSinohyriopsis cumingii (Unionidae, Indotropical)

The January 2018 Mussel of the Month is Sinohyriopsis cumingii. Sinohyriopsis is a genus of two species in eastern Asia.

At the close of 2017, there was an explosion of new freshwater mussel genera. Counting on our fingers, we have gained 8 new ones on our checklist, principally from two articles: Bolotov et al. (2017) and Williams et al. (2017). Parvaspina and Trapezidens where described as new, pulling species from Pleurobema and Trapezoideus, respectively. The other six were raised from synonymy to accommodate new classifications:

• Utterbackiana from Utterbackia,
Reginaia from Fusconaia,
Eurynaia from Elliptio,
• Bineurus and Monodontina from Pseudodon, and
• Sinohyriopsis from Hyriopsis.

We know of still more genus-level revisions coming down the pike.

Sinohyriopsis cumingii was removed from the genus Hyriopsis because true Hyriopsis are classified in the subfamily Rectidentinae, whereas phylogenetic analysis places S. cumingii with the genera of the Gonideinae (Lopes-Lima et al., 2017).

Although the taxonomy of this mussel was largely a guess until recently, it is actually a well-studied mollusk. For example, of all freshwater mussels, Sinohyriopsis cumingii has the richest set of sequences available on Genbank (155). That is, there are sequences for more than 150 different named genes and haplotypes owing to the large number of nuclear protein coding loci that have been characterized. References to many of the studies associated with those sequences can be found here. Sinohyriopsis schlegelii is in 2nd place with 48, and Cristaria plicata has 40. Compare those with 7 for Lampsilis cardium.

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