Mussel of the

Page last updated
1 September 2009

Mussel of the Month

The September 2009 Mussel of the Month is Diplodon chilensis. Diplodon is a large South American genus of eighteen species.

Diplodon chilensis
BMNH 1854.12.4.850. Rio Negro, Patagonia (type of U. patagonica).

The historic concept of Diplodon (as applied by Parodiz, 1968 and Haas, 1969, for example) has recently been split into two genera: Diplodon s.s. and Rhipidodonta. This division is based upon the somewhat dubious character of whether or not the glochidia are parasitic upon fish. We would like to learn more about the evidence supporting non-parasitic life cycles for the several species currently placed in Rhipidodonta (Simone, 2006), but that is not what this Mussel of the Month is about.

The species diversity of Diplodon (+ Rhipidodonta) has traditionally been among the hardest questions to answer in the field of "uniöology." Until recently, the only two genus-wide treatments had been those of Parodiz (1968) and Haas (1969). Unfortunately, the two systems that they came up with were completely incompatible. This left us in a quandary for some time while we were compiling our global species checklist (Graf & Cummings, 2007): how to deal with the species of Diplodon? Fortunately, we were saved by the recent, nearly continent wide system proposed by Simone (2006).

As we said at the time (Graf & Cummings, 2007: 299),

"We hope our discussion and checklist of global freshwater mussel diversity will have the same effect that Simpson's (1900, 1914) did a century earlier: interest and discussion in the Unionoida will increase ..., and new data and analyses will test and refine the patterns we have described."

The online version of our checklist, Unionoida cum Grano Salis, can be found by clicking here.

Diplodon chilensis is one species that has since been revised. We listed D. chilensis and D. patagonicus as two separate species, from the western and eastern sides of the Andes in Chile and Argentina, respectively. But as explained by Parada & Peredo (2008), this arrangement as been regarded as incorrect for most of the 20th century! Rather, most systemists have regarded the eastern population as merely a subspecies, D. chilensis patagonicus.

We have updated our checklist to reflect this hypothesis, and we look forward to seeing where others can improve our understanding of freshwater mussel diversity by showing us how our assessment was incorrect.


Phylum Mollusca
Class Bivalvia
Subclass Palaeoheterodonta
Order Unionoida

Superfamily ETHERIOIDEA Deshayes, 1830

Family HYRIIDAE Swainson, 1840
Subfamily HYRIINAE s.s.
Tribe Rhipododontini Starobogatov, 1970

Genus Diplodon Spix & Wagner, 1827

Species Diplodon chilensis (Gray, 1828)

For more information about D. chilensis and the taxonomy of Dipldon, check out:
  • 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.
  • Haas, F. 1969. Superfamilia Unionacea. Das Tierreich (Berlin) 88: 663 pp.
  • Parodiz, J.J. 1968. Annotated catalogue of the genus Diplodon (Unionacea - Hyriidae). Sterkiana 30: 1-22.
  • Parada, E. & S. Peredo. 2008. Diplodon patagonicus (Bivalvia: Hyriidae): to be or not to be. Gayana 72: 266-267.
  • Simone, L.R.L. 2006. Land and Freshwater Molluscs of Brazil: An Illustrated Inventory of the Brazilian Malacofauna, Including Neighboring Regions of South America, Respect to the Terrestrial and Freshwater Ecosystems. EGB. Fapesp. São Paulo. 390 pp.
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