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Mussel of the
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Page last updated
6 August 2018

Mussel of the Month

The 2018 Mussels of the Month, so far...

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).

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* “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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