Freshwater mussels: winged floater (Anodonta nuttalliana)

(Bivalvia: Unionoida: Unionidae)

Profile prepared by Lisa Schonberg, the Xerces Society for Invertebrate Conservation

The winged floater lives in rivers and lakes with muddy or sandy bottoms, most frequently in low gradient areas of coastal watersheds at lower elevations. Their host fish species are unknown. The winged floater is found in California, Oregon, Washington, Nevada, possibly Idaho and Utah, and southern British Columbia. It is less common than other Northwest Anodonta species.

The genus Anodonta, commonly known as “floaters,” includes six of the eight currently recognized freshwater mussel species native to the western United States. The Anodonta are fast-growing generalists, and are more tolerant of lower dissolved oxygen levels than other native mussel species. They prefer the softer substrates, such as sand and silt, that are characteristic of permanently flooded wetlands, lakes, and reservoirs. The shells of Anodonta species are thinner and usually lighter colored than those of other Northwest genera. They also have a light colored interior, are generally rounded, and lack a prominent ridge on their shell. Much of the information on this page was adapted from the guide: Freshwater Mussels of the Pacific Northwest.

conservation status

Anodonta nuttalliana currently receives no state or federal protection and this species is subject to many of the same threats that have decimated freshwater mussels in the eastern United States. More research is needed on the taxonomic status and distribution of all Anodonta species in order to evaluate the conservation status of this species. The Xerces Society, in collaboration with members of the Pacific Northwest Native Freshwater Mussel Workgroup, is currently investigating the conservation status of this species.

photograph


Please contact The Xerces Society for information on how to obtain permission to use this photo.

description and taxonomic status

The winged floater can be up to 4.25 inches long. It is smaller than other western Anodonta species. It is elliptical or ovate in shape, with very thin valves. Its beak has up to 20 irregular single or douple-looped concentric ridges. The nacre is white or bluish.

The taxonomic status of Anodonta nuttalliana (Lea 1838) is currently under review. Chong et al. (2008) found that A. californiensis and A. nuttalliana belong to a single clade, which is highly divergent from the clade that A. oregonensis and A. kennerlyi belong to. The genetic work also suggests that the A. californiensis/A. nuttalliana clade is highly divergent from the clade that A. beringiana belongs to.

life history

The winged floater lives in rivers and lakes with muddy or sandy bottoms, most frequently in low gradient areas of coastal watersheds at lower elevations. Their host fish species are unknown.

distribution

The winged floater is found in California, Oregon, Washington, Nevada, possibly Idaho and Utah, and southern British Columbia. It is less common than other Northwest Anodonta species.

threats
Freshwater mussels are vulnerable to water level fluctuation and are thus threatened by the diversion of water for irrigation, water supply and power generation. Freshwater mussels rely on native fish as hosts during their immature, or glochidial, life stage. The replacement of native fish by introduced fish species may be the greatest threat to the reproduction of mussel populations. Because freshwater mussels are filter-feeders, they can be adversely impacted by sedimentation and the accumulation of pollutants in sediments.
references

Chong, J.P., J.C. Brim-Box, J.K. Howard, D. Wolf, T.L. Myers, and K.E. Mock. 2008. Three deeply divided lineages of the freshwater mussel genus Anodonta in western North America. Conservation Genetics.

Nedeau, E., A.K. Smith, and J. Stone. 2005. Freshwater Mussels of the Pacific Northwest. Pacific Northwest Native Freshwater Mussel Workgroup, Vancouver, Washington. 45 pp.

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