Mussel of the

Page last updated
2 February 2023

Mussel of the Month

The February 2023 Mussel of the Month is Lampsilis teres. Lampsilis, as currently recognized, is a genus of 26 Recent species, endemic to eastern North America.

Lampsilis (Simpsonunio)
USNM 3023a. Ohio R., Sedamsville, Ohio, USA (type of Lampsilis fallaciosus Smith, 1899)

When Simpson (1900) classified freshwater mussel species as Lampsilis, he had a much broader conception that we use today. Based mostly on conchological extrapolation, he divided the genus into four subgenera. After a century of augmenting Ortmann’s (1912, etc.) studies of freshwater mussel soft anatomy and the molecular phylogenetics of the last 30 years, Simpson’s single genus has been split into at least 14 modern genera. We say “at least” because the correspondence between Simpson’s classification and the one we use here isn’t as clean as the table below might suggest. Many of the modern genera have species that were classified by Simpson among different subgenera of Lampsilis sensu lato. And some of the species that Simpson classified as “Lampsilis” aren’t even regarded as lampsilines anymore. We have more and better data than Simpson did to see through the homoplasy of shell characters!

As of this writing, we have logged 64 published cladograms that have analyzed at least two species of Lampsilis. And, the thing is, most of the time Lampsilis — as recognized in the modern literature (e.g., Graf & Cummings, 2021; FMCS species list right now) — has not been recovered as monophyletic. This is documented on the Lampsilis Cladomics page.

Take for example, the cladogram by Inoue et al. (2020, fig. 4), taken from the Lampsilis Cladomics page.

There are four different clades of species classified as Lampsilis: the Lampsilis cardium clade (the type species of Lampsilis), the Lampsilis teres clade, the Ortmanniana clade that includes L. higginsii, and the L. radiata clade (which includes Lampsilis virescens).

Another way to look at this, based just on this cladogram, is that the monophyly of Lampsilis would be achieved if Ortmanniana ligamentina is classified as Lampsilis. But just looking at one cladogram doesn’t take into account the diversity of results from previous studies. If you scroll through the Lampsilis Cladomics page, you will discover that clades representing the four listed above are relatively consistent among analyses, but the relationships among those clades are not. It may turn out that when the dust settles, our current concept of Lampsilis gets broken into multiple genera — and L. higginsii gets reclassified as Ortmanniana (Frierson, 1927; Haas, 1969)!

It is odd that, given the current mania for revising freshwater genera based strictly on molecular phylogenetic results, Lampsilis non-monophyly hasn’t already been sorted. Lampsilis has been recognizable and taxonomically stable for a long time. This may explain why there are so few available genus names available to apply in a new classification. One genus-group name that is available is Simpsonunio Starobogatov, 1970 for Lampsilis teres (+ anodontoides). In anticipation of future genus-splitting, we have selected Lampsilis (Simpsonunio) teres as the Mussel of the Month.


Phylum Mollusca
Class Bivalvia
Subclass Palaeoheterodonta
Order Unionoida

Superfamily UNIONOIDEA Rafinesque, 1820
Family UNIONIDAE s.s.
Subfamily AMBLEMINAE Rafinesque, 1820
Tribe LAMPSILINI Ihering, 1901

Genus Lampsilis Rafinesque, 1820
(+ Simpsonunio Starobogatov, 1970)

Species Lampsilis teres (Rafinesque, 1920)
(+ Unio anodontoides Lea, 1831; Lampsilis fallaciosus Smith, 1899)

To find out more about the classification of Lampsilis, check out:
  • Graf, D.L. & K.S. Cummings. 2021. A 'big data' approach to global freshwater mussel diversity (Bivalvia: Unionoida), with an updated checklist of genera and species. Journal of Molluscan Studies 87(1). eyaa034 (36 pp.).
  • Frierson, L.S. 1927. A Classified and Annotated Check List of the North American Naiades. Baylor University Press, Waco, TX. 111 pp.
  • Haas, F. 1969. Superfamilia Unionacea. Das Tierreich 88: 1-663.
  • Inoue, K., J.L. Harris, C.R. Robertson, N.A. Johnson & C.R. Randklev. 2020. A comprehensive approach uncovers hidden diversity in freshwater mussels (Bivalvia: Unionidae) with the description of a novel species. Cladistics 36: 88-113.
  • Ortmann, A.E. 1912. Notes upon the families and genera of the najades. Annals of the Carnegie Museum 8: 222-365.
  • Simpson, C.T. 1900. Synopsis of the naiades, or pearly fresh-water mussels. Proceedings of the United States National Museum 22: 501-1044.

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