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 Simpsonaias ambigua    (Say, 1825)

Salamander Mussel 


MN Status:

threatened
Federal Status:
none
CITES:
none
USFS:
none


Group:

mussel
Class:
Bivalvia
Order:
Unionoida
Family:
Unionidae
Habitats:

(Mouse over a habitat for definition)


Simpsonaias ambigua

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Map Interpretation

Map Interpretation

  Basis for Listing

The salamander mussel is a widespread species in the Mississippi and Ohio river drainages, but one that is uncommon and rarely collected (Mathiak 1979; Oesch 1984; Clark 1985; Parmalee and Bogan 1998). In Minnesota, the salamander mussel historically occurred in the Mississippi River (based on the presence of a single relic shell at Hastings) but it is currently restricted to the lower St. Croix River, where it is rare. Given its limited distribution and narrow habitat requirements, the salamander mussel was listed as a threatened species in Minnesota in 1996.

  Description

The shell of the salamander mussel is elongate or oblong, with thin valves, and it reaches up to 5 cm (2 in.) long. The beak is raised slightly above the hinge line, and the beak sculpture consists of several thin ridges raised in the middle, forming an upside down V. The outside of the shell is yellowish-tan to dark brown, and rayless. The teeth are rudimentary, almost unnoticeable, with 1 small, thin pseudocardinal tooth present in each valve. The lateral teeth are absent, and the inner shell is whitish. The salamander mussel can be distinguished from the cylindrical papershell (Anodontoides ferussacianus) and the spectaclecase (Cumberlandia monodonta) by its teeth characteristics and beak sculpture.

  Habitat

The salamander mussel is very habitat specific, living only under flat rocks (Clark 1985) or under ledges of rock walls (D. Heath, Wisconsin DNR, pers. comm.), habitats also occupied by its glochidial host, the mudpuppy salamander (Necturus masculosus) (Howard 1915).

  Biology / Life History

Mussels are long-lived animals. Members of many species may live for several decades and in some instances, a century or more. They spend most of their lives buried in the bottom sediments of permanent water bodies, and often live in multi-species communities called mussel beds (Sietman 2003).

Mussels are primarily sedentary, but they can move around with the use of their foot, which is a hatchet shaped muscle that can be extended out between the valves (shells). A mussel will burrow its foot into the sediment and then contract it to pull itself slowly along the bottom of its aquatic habitat (Sietman 2003).

Mussels eat by filtering bacteria, protozoans, algae, and other organic matter out of the water. They draw water into their body through their incurrent siphon, remove food and oxygen with their gills, and then expel the filtered water through their excurrent siphon. Food particles are carried to the mussel's mouth by tiny hairlike cilia located on the gills. Waste is expelled through the excurrent siphon (Sietman 2003).

Mussels have a complex and distinctive reproductive cycle. Males release sperm into the water, which are drawn in by females through their incurrent siphon. Fertilized eggs are brooded in the female's gills, where they develop into tiny larvae called glochidia. The breeding season of the salamander mussel is unknown but it is probably bradytictic, with females brooding their young long-term before they are released as glochidia (Baker 1928). Once the glochidia are expelled from the female's gills, they attach to the gills of mudpuppy salamanders by clamping onto them with their valves. The glochidia live as parasites on the mudpuppy until they develop into juvenile mussels, at which point they detach from the mudpuppy and fall to the streambed as free-living mussels. The salamander mussel is the only freshwater mussel known to use the mudpuppy as a host for its glochidia (Howard 1915).

  Conservation / Management

Factors that potentially threaten the continued existence of the salamander mussel include high stream-flow variations on the St. Croix River caused by a hydropelectric dam operating on a seasonal peaking regime, and the threat of non-point and point source water and sediment pollution (U.S. Fish and Wildlife Service 1997). Dams, channelization, and dredging increase siltation and physically alter habitat conditions. The salamander mussel is also being impacted by the infestation of non-native zebra mussels (Dreissena polymorpha) in the Mississippi River and its tributaries. Zebra mussels can attach themselves in large numbers to the shells of native mussels, eventually causing death by suffocation.

  Conservation Efforts in Minnesota

A 10-year statewide mussel survey initiated by the Minnesota DNR in 1999 resulted in a better understanding of the salamander mussel's ecology and current status in Minnesota.

  References

Baker, F. C. 1928. The fresh water mollusca of Wisconsin. Part II Pelecypoda. Bulletin of the Wisconsin Geological and Natural History Survey 70:1-495.

Clarke, A. H. 1985. The tribe Alasmidontini (Unionidae: Anodontinae), Part II: Lasmigona and Simpsonais. Smithsonian Contributions to Zoology No. 399. 75 pp.

Doolittle, T. C. J. 1988. Distribution and relative abundance of freshwater mussels in the Saint Croix National Scenic Riverway. Final report submitted to the Natural Heritage and Nongame Research Program, Minnesota Department of Natural Resouces. Unpaged.

Howard, A. D. 1915. Some exceptional cases of breeding among the Unionidae. The Nautilus 29(1):4-11.

Mathiak, H. A. 1979. A river survey of the unionid mussels of Wisconsin 1973-1977. Sand Shell Press, Horicon, Wisconsin. 75 pp.

Oesch, R. D. 1984. Missouri naiades: a guide to the mussels of Missouri. Missouri Department of Conservation. Jefferson City, Missouri. 270 pp.

Parmalee, P. W., and A. E. Bogan. 1998. The freshwater mussels of Tennessee. The University of Tennessee Press, Knoxville, Tennessee. 328 pp.

Sietman, B. E. 2003. Field guide to the freshwater mussels of Minnesota. Minnesota Department of Natural Resources, St. Paul, Minnesota. 144 pp.

United States Fish and Wildlife Service. 1997. Winged Mapleleaf Mussel (Quadrula fragosa) recovery plan. United States Fish and Wildlife Service, Ft. Snelling, Minnesota. 359 pp.