The phylum Mollusca includes a diversity of species that inhabit oceanic, freshwater and terrestrial habitats – from octopus and squid to clams, mussels, snails and slugs. Two major classes of mollusks include the bivalves and the gastropods. Bivalvia means “two doors,” or in this case, two halves of a shell, and includes mussels and clams. They have a large, strong foot for locomotion, and two tubes with which they pull water into the body, filter out food, then push the used water back out of the body. Gastropoda means “stomach foot,” and includes the snails, slugs and limpets. These diverse and important mollusks slide along the ground scraping up food with a rasp-like mouthpart called a radula.

It is believed that there are approximately 100,000 species of mollusks that exist today, and about 70,000 additional extinct mollusk species. In North America, approximately 69% of all freshwater mussels are either extinct, imperiled, or vulnerable to extinction, representing the most at-risk group of all plants and animals. These aquatic animals are most threatened by changes made to their habitat. The Xerces Society is working to conserve freshwater mussels in western North America by reviewing the status of each species. Xerces also uses the Endangered Species Act to advocate for the conservation of a number of snail, limpet and abalone species.


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Mussel bed composed of Anodonta sp. and Gonidea angulata, Middle Fork John Day River, Oregon. Copyright CTUIR freshwater mussel project.