Quadrula quadrula (Rafinesque, 1820)
Other common names: Stranger.
Key characters: Fairly thick shell with well-developed teeth. Squared in outline, lateral surface with two rows of pustules separated by a sulcus.
Similar species: Winged mapleleaf, pimpleback, purple pimpleback, monkeyface, wartyback.
Description: Shell quadrate to rounded, thick, and somewhat inflated. Anterior end rounded, posterior end squared or truncated. Dorsal margin straight, ventral margin curved in the anterior half, straight or arched posteriorly. Umbos small and only slightly elevated above the hinge line. Beak sculpture of two rows of raised bumps or nodules that continue downward on the surface of the shell, separated by a furrow or sulcus. Rows of ridges or pustules on either side of sulcus and on posterior slope, rest of surface usually smooth. Periostracum variable, from yellowish green to light brown with faint rays in small shells, becoming greenish brown, chestnut, or dark brown in larger individuals. Length to 4 inches (10.2 cm).
Pseudocardinal teeth well developed, serrated; two in the left valve (occasionally with a small tooth on either side), one in the right. Lateral teeth striated, fairly long, and straight; two in the left valve, one in the right. Beak cavity deep. Nacre pearly white, iridescent posteriorly.
Habitat: Medium to large rivers and reservoirs with a mud, sand, or gravel bottom.
Status: Widespread and common. Commercial species.