Mussel of the

Page last updated
1 June 2009

Mussel of the Month

The June 2009 Mussel of the Month is Epioblasma flexuosa. Epioblasma is a highly endangered genus of 20 species found in eastern North America.

Epioblasma flexuosa
top left: ANSP 56571. Ohio (type of Unio foliatus Hildreth, 1828). Female.
bottom right: ANSP 20249. Kentucky River (type of Obliquaria (Quadrula) flexuosa Rafinesque, 1820). Male.

Over the last few years there has been quite a burst of activity to study the remaining species of the genus Epioblasma. This is not too surprising as many of the species are extinct, the remaining species are under state and/or federal conservation protection, and they are REALLY interesting from a biological perspective. It is this last aspect that we want to focus on here.

Epioblasma species, like many other lampsilines, are sexually dimorphic. That is, males and females look different from each other, aside from morphological differences in their reproductive structures. Specifically, many lampsilines have sexually dimorphic shells. This may seem trivial since lots of taxa are sexually dimorphic: e.g., cardinals and bighorn sheep. However, the difference in this case is that males of those species use those morphological traits to compete for mates (i.e., sexual selection). Freshwater mussels don’t copulate or physically interact with each other (as far as we know), so what difference could it make to one Epioblasma what another one looks like?

It turns out that the shells of female Epioblasma species are reproductive structures. On Chris Barnhart’s Unio Gallery, you can see some jaw-droppingly cool video of various mussels (not E. flexuosa, but other species) using their shells to grab and hold their host fish. If that doesn’t blow your mind, then you should think about it some more.


Phylum Mollusca
Class Bivalvia
Subclass Palaeoheterodonta
Order Unionoida

Superfamily UNIONOIDEA Rafinesque, 1820

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

Genus Epioblasma Rafinesque, 1831
[= Dysnomia Agassiz, 1852]

Species Epioblasma flexuosa (Rafinesque, 1820)

For more information about the species of the genus Epioblasma, check out:
  • Barnhart, M.C. Unio Gallery at Missouri State University.
  • Johnson, R.I. 1978. Systematics and zoogeography of Plagiola (= Dysnomia = Epioblasma), an almost extinct genus of freshwater mussels (Bivalvia: Unionidae) from middle North America. Bulletin of the Museum of Comparative Zoology 148: 239-321.
  • Zanatta, D.T. & R.W. Murphy. 2008. The phylogeographical and management implications of genetic population structure in the imperiled snuffbox mussel, Epioblasma triquetra (Bivalvia: Unionidae). Biological Journal of the Linnean Society 93: 371-384. [And numerous useful references cited therein.]
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