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Cyprogenia stegaria

ListedJune 21, 1990
FamilyUnionidae (Freshwater Mussel)
DescriptionMottled yellow shell with green rays and a silvery white interior.
HabitatGravel riffles in streams.
FoodFilter feeder.
ReproductionFemale retains fertilized eggs in gills until larvae fully develop.
ThreatsImpoundments, sand and gravel mining, water pollution.
RangeAlabama, Illinois, Indiana, Kentucky, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia


Cyprogenia stegaria is commonly called the fan-shell var. C. irrorata. A member of the Unionidae family (freshwater mussels), the fanshell has a medium-sized, subcircular shell that seldom exceeds 3.2 in (8.1 cm) in length. The exterior of the shell has green rays on a light green or yellow surface ornamented with green mottling. Strong concentric ridges cover the shell's lower surface. The interior of the shell is usually silvery white, sometimes flesh-colored.


The fanshell's specific food habits are unknown; but, it likely feeds on food items similar to those consumed by other freshwater mussels. Freshwater mussels are known to feed on detritus, diatoms, phytoplankton, and zooplankton that they filter out of the water.

Although the fanshell's reproductive biology is unknown, it probably reproduces like other freshwater mussels. Males release sperm into the water column. The females take in the sperm through their siphons during feeding and respiration. The fertilized eggs are retained in the gills until the larvae (glochidia) fully develop. When the glochidia are released into the water, they attach and encyst on the gills or fins of a fish host. When metamorphosis is complete, they drop to the streambed as juvenile mussels. The species of fish host utilized by the fan-shell and the habitat used by the juveniles are unknown.


The fanshell inhabits medium to large rivers. It has been reported primarily from relatively deep water in gravelly substrate with moderate current.


Since the turn of the twentieth century, the fan-shell has undergone a substantial range reduction. It was historically widely distributed in the Ohio, Wabash, Cumberland, and Tennessee Rivers and their larger tributaries in Pennsylvania, Ohio, West Virginia, Illinois, Indiana, Kentucky, Tennessee, Alabama, and Virginia. Reproducing fanshell populations are now present in only three riversthe Clinch River, Hancock County, Tennessee, and Scott County, Virginia; the Green River, Hart and Edmonson Counties, Kentucky; and the Licking River, Kenton, Campbell, and Pendleton Counties, Kentucky.

Additionally, small remnant, apparently nonre-producing, populations may still occur in the Muskingum River in Morgan and Washington Counties, Ohio; the Walhonding River in Coshocton County; the Wabash River in White County, Illinois, and Posey and Wabash Counties, Indiana; the East Fork White River, Martin County, Indiana; the Tippecanoe River, Tippecanoe County, Indiana; the Kanawha River, Fayette County, West Virginia; Tygart Creek, Greenup and Carter Counties, Kentucky; the Barren River, Allen and Barren Counties, Kentucky; the Cumberland River, Smith County, Tennessee; and the Tennessee River, Rhea, Meigs, and Hardin Counties, Tennessee.

The population in the Green River is likely the best of the three remaining reproducing populations. Freshly dead fanshells of various age classes from juvenile to adult were found in 1988 in muskrat middens along the Green River. The Clinch River population extends over about 86 river mi (138.4 km). However, a Tennessee Valley Authority survey reported that the fanshell comprised less than 1% of the mussels collected at 11 Clinch River quantitative sampling sites in 1979 and 1988. In the Licking River, live and fresh-dead individuals of several year classes have been collected.


The distribution and reproductive capacity of this species has been seriously impacted by the construction of impoundments and navigation facilities, dredging for channel maintenance, sand and gravel mining, and water pollution. The three reproducing populations are threatened by a variety of factors. The Green River has been degraded by runoff from oil and gas exploration and production sites and by alteration of stream flows by an upstream reservoir. Land use practices along the Clinch River have contributed to a decline in water quality and mussel populations. The Clinch River has also experienced some adverse impact from coal mining, and the river has been subjected to two mussel kills resulting from toxic substance spills from a riverside coal-fired power plant. At least 30 collecting sites on the Clinch River once contained more than 18 different species of freshwater mussels. Now, the mussel abundance in the Clinch River has decreased from an average of 11.64 mussels per 10.8 sq ft (1 sq m) in 1979, to six mussels per 10.8 sq ft (1 sq m) by 1988.

The species probably has its highest population density in the Green River, but runoff from oil and gas exploration and production is polluting the river. Stream flows have been altered by an upstream reservoir, and this is also causing problems. At one time, 66 species of mussels inhabited this river; now, only about 40 species are known to survive. Since the fanshell's population density is extremely low and only three of the 12 known populations are reproducing, about 75% of populations could be eliminated soon.

The third reproducing population, located in the Licking River, could potentially be threatened by some of the water supply development alternatives presently under preliminary review for the Licking River watershed and by wastewater discharges.

In addition, most of the fanshell populations are small, and all the populations are geographically isolated from each other. This isolation restricts the natural interchange of genetic material between the populations, and the small population size reduces the reservoir of genetic variability within the populations.

Conservation and Recovery

The recovery criterion called for the establishment of at least 12 viable populations, which might be difficult to achieve because much of the species habitat has been destroyed. The Fanshell Technical/Agency Draft Recovery Plan identifies the following tasks as actions needed to achieve recovery: (1) utilize existing legislation and regulations to protect species; (2) search for new populations and monitor existing populations; (3) develop and utilize an information and education program; (4) determine species' life history requirements; (5) determine threats and alleviate those that threaten the species' existence; and (6) through reintroduction and protection, establish nine viable populations. Mussel propagation and some life history research were initiated by 2000.


U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345

U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1 Federal Drive
BHW Federal Building
Fort Snelling, Minnesota 55111
Telephone: (612) 713-5360

U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
300 Westgate Center Dr.
Hadley, Massachusetts 01035-9589
Telephone: (413) 253-8200
Fax: (413) 253-8308

U.S. Fish and Wildlife Service
330 Ridgefield Court
Asheville, North Carolina 28806
Telephone: (704) 665-1195


Ahlstedt, Steven A. January 1986. "Cumberland Mollusk Conservation Program. Activity 1 Mussel Distribution Surveys." Tennessee Valley Authority, Norris (TN).

Bates, J. M. and S. D. Dennis. 1985. "Mussel Resource SurveyState of Tennessee." Technical Report No. 85-4. Tennessee Wildlife Resources Agency.

Cummings, K. S., C. A. Mayer, and L. M. Page. 1988."Survey of the Freshwater Mussels [Mollusca Unionidae] of the Wabash River Drainage, Phase 11: Upper and Middle Wabash River." Technical Report. Illinois Natural History Survey.

Gordon, M., and J. Layzer. 1989. "Mussels (BIVALVIA UNIONOIDEA) of the Cumberland River Review of Life Histories and Ecological Relationships." Biological Report 89 (15). U.S. Fish and Wildlife Service.

Starnes, L. B. and A. E. Bogan. 1988. "The Mussels (Mollusca Bivalvia Unionidae) of Tennessee." American Malacologocal Bulletin 6 (1): 19-37.

U.S. Fish and Wildlife Service. 21 June 1990. "Endangered and Threatened Wildlife and Plants Designation of the Fanshell as an Endangered Species." Federal Register 55 (120): 25591-25595.

U. S. Fish and Wildlife Service. 1990. "Fanshell Technical/Agency Draft Recovery Plan." U.S. Fish and Wildlife Service, Atlanta.