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COSEWIC assessment and status report on the Rocky mountain ridged mussel Gonidea angulata in Canada

Special Significance of the Species

This species is the only known living taxon in this genus. The monospecific Gonidea, however, has an extensive fossil record in the western portions of the U.S., dating at least to the Miocene (5 million years or more: Taylor, 1988, Watters, 2001; e.g., Gonidea coalingensis, Taylor, 1985). It has occurred essentially in its present range since the Late Cenozoic (Neogene). The genus is taxonomically isolated and not closely related to any of the numerous eastern North American forms (Lydeard et al., 1996; Watters, 2001). There may be one additional living species from Korea (Taylor, 1988), thus providing one of the most significant examples of the Asian affinities of the western North American freshwater mollusc fauna. It is particularly characteristic of the unique and sparse Pacific freshwater mussel faunal province (Taylor, 1985, 1988).

First Nations’ use of this species has been documented from the Interior Columbia Basin. Freshwater mussel shell middens have been located in British Columbia, Montana, Idaho, Nevada, Oregon, Washington, and California (Lyman 1980). The Flathead First Nations of Montana and the Umatilla First Nations in Oregon have used freshwater mussels such as G. angulata, M. falcata, and Anodonta species for food, tools, and ornamentation. Investigation of freshwater mussel shell middens in certain areas has detected a shift in species use from M. falcata to G. angulata, the reasons for which are unknown. However, there is reason to speculate that the aggradations of certain rivers (as mentioned in Vannote and Minshall 1982) could have resulted in an overall shift in species composition, or at least to an increase in suitable G. angulata habitat while limiting the availability of M. falcata habitat.