Rock Pocketbook
Arcidens confragosus (Say)

Status: State Threatened (August 1, 1989).

Occurence: Occurs in the Mississippi River and the lower Wisconsin River.

Aid to ID: Shell is thin to moderately thick and inflated. Umbos are elevated and located near the middle of the shell. Sculpturing consists of two rows of knobs that continue onto the posterior part of the shell and form into folds. The outside of the shell is olive-green to green. Larger shells become black, thicken and may lose the crinkly appearance, while the younger, smaller shells are greenish. Pseudocardinal teeth are narrow and elongated, while lateral teeth are indistinct. Nacre is white and iridescent posteriorly. Length to 7 inches (17.8 cm).

Habitat: Most often found in sluggish water at shallow depths of less than one meter on a firm mud bottom. Inhabitants of quiet pools on a mud or stable sand bottom.

Management Considerations: 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 content for this page was originally presented in the Endangered and Threatened Invertebrates of Wisconsin, a free publication available by contacting the Endangered Resources Program.