Quadrula metanevra (Rafinesque, 1820)
Other common names: Knobbed rock shell.
Key characters: Rounded or squared shell with large knobs along the posterior ridge and a distinct indentation on the posterior margin that looks like a chimpanzee in profile. Distinctive zigzag markings on the shell (may be lacking in older individuals).
Description: Shell thick, rounded or rectangular, and moderately inflated. Anterior end rounded, posterior end squared or truncated and indented in the middle. Dorsal margin straight, area behind the umbos flattened into a wing, ventral margin curved. Umbos elevated above the hinge line. Beak sculpture of pronounced ridges or knobs that continue down the posterior ridge to the ventral margin of the shell. Shell rough, with numerous pustules on the anterior half and behind the umbos and a row of large knobs along the posterior ridge. Periostracum green or light brown (darker in older shells) with yellow zigzag or chevron-shaped markings on the shell. Length to 4 inches (10.2 cm).
Pseudocardinal teeth serrated and well developed; two in the left valve, one in the right (occasionally with a small tooth on either side). Lateral teeth short, heavy, serrated and straight; two in the left valve, one in the right. Beak cavity deep. Nacre pearly white, iridescent posteriorly.
Habitat: Medium to large rivers in gravel or mixed sand and gravel.
Status: Relatively uncommon but may be locally abundant. Endangered in Ohio. Threatened in Wisconsin.