Endangered Resources Program Species Information
Bullhead (Plethobasus cyphyus)

Overview

Species Overview

Bullhead (Plethobasus cyphyus), also commonly referred to as Sheepnose, a State Endangered mussel and currently under review by the US Fish and Wildlife Service for federal listing. This species is found in clean water of large rivers in the Western part of the state. It prefers a stable sand substrate but has been found in mixed sand and gravel. It is always rare where it is found. The only known fish host that has been reported is the sauger.

Status and NHI Documented Occurrences in Wisconsin

The table below provides information about the protected status (State and Federal Status) and the rank (S and G Ranks) for Bullhead (Plethobasus cyphyus). See the Working List Key for more information about the abbreviations used. Counties shaded blue have documented occurrences for this species in the Wisconsin Natural Heritage Inventory database. For invertebrates, dots depict locations from the "Invertebrate Atlas," a database with occurrences of rare and common aquatic and select terrestrial invertebrate species found in Wisconsin and adjacent areas. While the invertebrate atlas is a quality assured database, not all records have been verified. The map is provided as a general reference of where this species has been found to date and is not meant as a range map.

Summary Information State Status: END Federal Status in Wisconsin: C State Rank: S1 Global Rank: G3 Tracked by NHI: Y Species of Greatest Conservation Need: Y

Detailed Information

Identification: Elongated heavy, brown shell with several radial knobs on disc. The anterior end is rounded and the posterior end bluntly pointed. Epidermis is yellowish-brown in smaller shells and darker brown in older shells. Pseudocardinal and lateral teeth are heavy. The nacre is white. Length to 5 inches (12.7 cm).

Habitat: Found in large rivers with a rapid current where it lives on mud, sand or gravel bottoms in water 1-2 m. deep.

State Distribution: Occurs in the upper and lower reaches of the Wisconsin River as well as the Chippewa and the Flambeau Rivers.

Phenology: Host fish for this species is the sauger (Stizostedion canadense). Mussels are gravid and/or infesting fish from May through July.

Management Guidance: Habitat destruction and river pollution have resulted in mussel declines. Protection of habitat and improvements in water quality along with restriction of dredging, impoundments, sand and gravel mining, and navigational improvements would benefit this species. The development of fish runways to facilitate the movement of host species through or around dams could help to protect this species.

Information compiled from publication PUB-ER-085-99 (now out-of-print).

Photos

Click on a photo to view a larger version. Please considering donating your photos to the Endangered Resources Program for educational uses. See also information regarding use of photos

Photo ©  Illinois Natural History Survey.

Related Links

Links to Additional Bullhead Information

• MN Department of Natural Resources [Exit DNR]
• Illinois Natural History Survey [Exit DNR]

Other Links Related to Mussels and Clams

• Illinois Natural History Survey [Exit DNR]
• The Field Museum [Exit DNR]
• Conchologists of America [Exit DNR]
• EPA Biological Indicators of Watershed Health [Exit DNR]
• Milwaukee Public Museum [Exit DNR]