Mussel of the

Page last updated
1 May 2008

Mussel of the Month

The May 2008 Mussel of the Month is Quadrula quadrula. Quadrula is a fantastically sculptured genus of four species from eastern North America.

Plieodon ovata
ANSP 20224. Salt River, Kentucky. (Neotype).

We have recently proposed some taxonomic changes to old genus Quadrula based upon some recent molecular work. It is appropriate for us, then, to use the opportunity of Q. quadrula's status as Mussel of the Month to discuss those revisions.

The tradiational taxon of Quadrula (as listed in Burch, 1975 and Turgeon et al., 1998) contained 19 species, in addition to the species Tritogonia verrucosa. Contrary to this long-held system for these species, the molecular phylogenetic study by Serb et al. (2003) recovered Quadrula as paraphyletic, with Tritogonia nested with the larger Quadrula clade. One conclusion that could have been derived from this result would be to sink T. verrucosa into Quadrula, and that would have been perfectly reasonable.

However, Serb et al. also found that the relationships among the species of Quadrula conformed quite nicely to the traditionally-recognized species groups and some already-named subgenera. Rather than bury all the information gained by that splendid analysis, we (Graf & Cummings, 2007) simply elevated the subgenera to genera. This action not only retains Tritogonia but splits the old Quadrula into three genera: Quadrula, Theliderma and Amphinaias.

Quadrula apiculata Amphinaias archeri
  fragosa   asperata
  quadrula   aurea
  rumphiana   couchiana
Theliderma cylindrica   houstonensis
  intermedia   nodulata
  metanevra   petrina
  sparsa   pustulosa
  stapes   refulgens
  tuberosa Tritogonia verrucosa



Phylum Mollusca
Class Bivalvia
Subclass Palaeoheterodonta
Order Unionoida

Superfamily UNIONOIDEA Rafinesque, 1820

Family UNIONIDAE Rafinesque, 1820
Subfamily AMBLEMINAE Rafinesque, 1820
Tribe QUADRULINI von Ihering, 1901

Genus Quadrula Rafinesque, 1820

Species Quadrula quadrula (Rafinesque, 1820)

For more information about Quadrula and its systematics, check out:
  • Burch, J.B. 1975. Freshwater Unionacean Clams (Mollusca: Pelecypoda) of North America. [Revised Edition]. Malacological Publications. Hamburg, Michigan. 204 pp.
  • Graf, D.L. & K.S. Cummings. 2007. Review of the systematics and global diversity of freshwater mussel species (Bivalvia: Unionoida). Journal of Molluscan Studies 73: 291-314.
  • Serb, J.M. J.E. Buhay & C. Lydeard. 2003. Molecular systematics of the North American freshwater bivalve genus Quadrula (Unionidae: Ambleminae) based on mitochondrial ND1 sequences. Molecular Phylogenetics and Evolution 28: 1-11.
  • Turgeon et al. 1998. Common and scientific names of aquatic invertebrates from the United States and Canada: Mollusks. 2nd Edition. American Fisheries Society, Special Publication 26. 526 pp.
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