Image from MUSSEL Project Web Site.

The Bivalvia is one of two classes of the Phylum Mollusca that has representatives in fresh waters. There are probably somewhere around 10,000 bivalve species in marine and freshwaters (notice only one significant digit), and about 10% are found in inland and near-shore habitats (Bogan, 2008). Graf (2013) provided a comprehensive review of global freshwater bivalve diversity and estimated the number of truly freshwater species to be c. 1200. Of these, almost 350 occur in North America.

Bivalves are recognizable for their two shells (= valves), reduced cephalization, and enlarged ctenidia for filter-feeding. All native North American freshwater bivalves exhibit parental care in the form of larval brooding. Among the freshwater mussels (Order Unionoida), the life cycle is further elaborated by a parasitic larval stage. The Family Sphaeriidae -- also known as fingernail, pill, and pea clams -- are direct-developers, producing crawl-away juveniles. In addition to these, two exotic genera are also established in North America: Dreissena and Corbicula.

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Bibliography

• Graf, D.L. 2013. Patterns of freshwater bivalve global diversity and the state of phylogenetic studies on the Unionoida, Sphaeriidae, and Cyrenidae. American Malacological Bulletin 31: 135-153.
• Cummings, K.S. & D.L. Graf. 2010. Mollusca: Bivalvia. [in] J.H. Thorp & A.P. Covich (eds.). Ecology and Classification of North American Freshwater Invertebrates, 3rd edition: 309-384.
• Bogan, A.E. 2008. Global diversity of freshwater mussels (Mollusca, Bivalvia) in freshwater. Hydrobiologia 595: 139-147. [Available online]
• 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.
• Smith, D.G. 2001. Mollusca (Gastropods, pelecypods). Pennak's Freshwater Invertebrates of the United States, 4th edition: 327-400.
• Cummings, K.S. & C.A. Mayer. 1992. Field Guide to Freshwater Mussels of the Midwest. Illinois Natural History Survey Manual 5. 194 pp. [Available online]
• Underhill, J.C., W.D. Schmid & D.E. Gilbertson. 1982. Taxonomic Keys to the Common Animals of the North Central States, exclusive of the parasitic worms, terrestrial insects, and birds, 4th edition. 205 pp.
• Burch, J.B. 1972. Freshwater sphaeriacean clams (Mollusca: Pelecypoda) of North America. U.S. Environmental Protection Agency, Biota of Freshwater Ecosystems Identification Manual 3. 31 pp. [Available online]
• Clench, W.J. 1959. Mollusca. [in] W.T. Edmondson (ed.). Ward & Whipple Fresh-Water Biology, 2nd edition: 1117-1160.
• Baker, F.C. 1928. The fresh water Mollusca of Wisconsin. Part II. Pelecypoda. Bulletin of the Wisconsin Geological and Natural History Survey 70(2): i-vi, 1-495.
• Baker, F.C. 1924. The fauna of the Lake Winnebago region: A quantitative survey with special reference to the Mollusca. Transactions of the Wisconsin Academy of Sciences, Arts & Letters 21: 109-146. [Available online]

Student Essays

• "The Decline of Order Unionoida Bivalves in Wisconsin Due to Dreissenid Introductions" by Hans Klopp (BIOL/WATR 361, Fall 2012 )
• "Family Unionidae (Mollusca: Bivalvia) native to Wisconsin and the Ecology of Non-Threatened or Endangered Species within this Family" by Andrew Teal (BIOL/WATR 361, Fall 2012 )

Web Pages

• A Wisconsin Bestiary
• Animal Diversity Web
• Integrated Taxonomic Information System
• MUSSEL Project Web Site
• Tree of Life
• Unio Gallery
• WikiSpecies
• Wikipedia
• Wisconsin's Rare Mussels and Clams
• World Register of Marine Species