Mussel of the

Page last updated
30 March 2018

Mussel of the Month

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

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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