THE XERCES SOCIETY FOR INVERTEBRATE CONSERVATION

Aquatic Invertebrates in Pacific Northwest Freshwater Wetlands
An Identification Guide and Educational Resource

The California floater is the species of greatest concern within the Anodonta.  Its historical range encompassed the west coast from Baja California to southern British Columbia, and east beyond the Continental Divide.  It has been extirpated from most of its historical range in California and Arizona.  Remnant populations remain in Arizona, and in Washington in the Columbia and Okanogan Rivers watersheds. 

The California Floater inhabits shallow muddy or sandy habitat in large rivers, reservoirs and lakes.  It’s full range of host species are unknown, but it may use native minnow species and an introduced mosquito fish.  The California Floater is a federal species of concern, and it is a candidate for protection in Washington.  The main reasons for its decline are thought to be water diversion and competition from non native species. 

Size: xlarge
Identifying feature(s): the posterior part of the shell (the longer of the two sides from the hinge out) is higher than the anterior part, giving the overall shell a more circular appearance (not oblong); shell is similar in thickness to that of other Anodonta species.
Habitat: soft-bottomed rivers, reservoirs and lakes
Tolerance: moderate