About 264 species occur in the freshwater of North America. Recognition Laterally compressed mollusks with a bivalved shell with a dorsal hinge. The head is poorly developed. The mantle cavity is capacious, the gills are large and serve also in feeding. Life Cycle Marine forms normally have external fertilization and free-swimming trochophore and veliger larvae , freshwater forms usually shed the sperm into the water, but the eggs are fertilized and brooded within the gill cavity.
Most species complete the live cycle in a month to a year.
Their eggs are brooded until the glochidia larval stage is achieved. The glochidia are parasitic on fish or aquatic amphibians. The glochidia transforms to a young mussel in a few days to few weeks and drops to the bottom to begin feeding as an adult. Breeding may be limited to the spring or throughout most of the year. Adults may hibernate or remain active throughout the winter.