Venustaconcha ellipsiformis (Conrad, 1836)
Basis for Listing
The ellipse went undetected in Minnesota until 1983, when it was discovered by the Minnesota DNR during a survey of the Straight River (Davis 1987). Little was known at the time about the species' distribution and status in the state, but the available data indicated it was uncommon and in need of protection. More recent sampling for this mussel in southern Minnesota has revealed populations in the Cannon (Davis 1987), Zumbro (Bright et al. 1988), Root, Cedar, and Upper Iowa river systems. The ellipse is the most common species in the upper tributaries of the Root River system, but populations in the other rivers do not appear to be as large. Relic shells are very rare from the Minnesota River Drainage, indicating it was historically present in that system in low numbers, but is likely extirpated there now. There are also a few historic records from the Mississippi River. Given its limited range and sparse population, the ellipse was listed as a threatened species in Minnesota in 1996.
The shell of the ellipse is generally small, reaching up to 10 cm (4 in.) long, and oblong with a bluntly pointed posterior. The shell is stout for its size. The outside of the shell is yellowish green to brown with green rays that become fine and wavy on the posterior half of the valve. The beak sculpture consists of fine double-looped lines, which are usually obscure. The pseudocardinal and lateral teeth are well developed and heavy for their size, and the inside of the shell is white with a shallow beak cavity. The ellipse resembles the mucket (Actinonaias ligamentina) and the spike (Elliptio dilatata) mussel.
The ellipse occurs primarily in the headwater reaches of rivers in gravel riffles (van der Schalie and van der Schalie 1963) and silty areas along stream banks.
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).
Conservation / Management
Degradation of mussel habitat in streams throughout the ellipse's known range is a continuing threat to the species. Like most other freshwater mussels, the ellipse is vulnerable by virtue of its dependence on fish hosts for the metamorphism of its larvae (Neves 1993). Williams et al. (1993) considered the creation of dams and the ensuing siltation, dredging, and change in water flow, to be the most important threat leading to the extinction and extirpation of freshwater mussels. Impoundments change stream flows, which can in turn increase sedimentation rates and affect the physiological processes of mussels. Dams may also eliminate a mussel's requisite host fish species. Competition from other fish species may also locally reduce or eliminate the required host fish species from the environment. As a consequence, if the host species disappears from the river or stream, the mussel species will soon be extirpated from the habitat as well. To prevent the extirpation of mussel species, both the mussel and the host fish species must be preserved.
Conservation Efforts in Minnesota
A 10-year statewide mussel survey initiated by the Minnesota DNR in 1999 resulted in a better understanding of the ellipse's ecology and current status in Minnesota.
References and Additional Information
Allen, D. C., B. E. Sietman, D. E. Kelner, M. C. Hove, J. E. Kurth, J. M. Davis, J. L. Weiss, and D. J. Hornbach. 2007. Early life-history and conservation status of Venustaconcha ellipsiformis (Bivalvia, Unionidae) in Minnesota. American Midland Naturalist 157:74-91.
Bright, R. C., E. Plummer, and D. Olson. 1988. A survey of the mussels of the Zumbro River drainage, southeastern Minnesota. Report submitted to Minnesota Department of Natural Resources. 27 pp. + tables, figures, and appendices.
Davis, M. 1987. Freshwater mussels (Mollusca: Bivalvia: Unionidae) of the Cannon River drainage in southeastern Minnesota. Final report submitted to the Nongame Wildlife Program, Minnesota Department of Natural Resources. 21 pp. + figures and original data sheets.
Dawley, C. 1947. Distribution of aquatic mollusks in Minnesota. American Midland Naturalist 38:671-697.
Kelner, D., M. Davis. 2002. Final report: mussel (Bivalvia:Unionidae) survey of the Mississippi National River and Recreation Area Corridor, 2000-01. Final report submitted by the Minnesota Department of Natural Resources. 44 pp. + appendices.
Neves, R. J. 1993. A state-of-the-unionids address. Pages 1-10 in K. S. Cummings, A. C. Buchanan, and L. M. Koch, editors. Conservation and management of freshwater mussels. Proceedings of a UMRCC Symposium, 12-14 October 1992, St. Louis, Missouri. Upper Mississippi River Conservation Committee, Rock Island, Illinois. 189 pp.
Riusech, F. A., and M. C. Barnhart. 2000. Host suitability and utilization in Venustaconcha ellipsiformis and Venustaconcha pleasii (Bivalvia: Unionidae) from the Ozark Plateaus. Pages 83-91 in R. A. Tankersley, D. I. Warmolts, G. T. Watters, B. J. Armitage, P. D. Johnson, and R. S. Butler, editors. Freshwater Mollusk Symposia Proceedings. Part I. Proceedings of the Conservation, Captive Care and Propagation of Freshwater Mussels Symposium. Ohio Biological Survey Special Publication, Columbus, Ohio.
Sietman, B. E. 2003. Field guide to the freshwater mussels of Minnesota. Minnesota Department of Natural Resources, St. Paul, Minnesota. 144 pp.
van der Schalie, H., and A. van der Schalie. 1950. The mussels of the Mississippi River. American Midland Naturalist 44:448-464.
van der Schalie, H., and A. van der Schalie. 1963. The distribution, ecology, and life history of the mussel, Actinonaias ellipsiformis (Conrad), in Michigan. Occasional Papers of the Museum of Zoology, University of Michigan No. 633. 17 pp.
Williams, J. D., M. L. Warren, Jr., K. S. Cummings, J. L. Harris, and R. J. Neves. 1993. Conservation status of freshwater mussels of the United States and Canada. Fisheries 18(9):6-22.