Pleurobema cordatum (Rafinesque, 1820)
Other common names: Pigtoe.
Key characters: Triangular shell, umbos projecting forward, sulcus present, deep beak cavity.
Similar species: All other pigtoes (Fusconaia and Pleurobema).
Description: Shell moderately thick, triangular, and moderately inflated. Anterior end rounded, posterior end bluntly pointed. Dorsal margin straight, ventral margin curved anteriorly, straight posteriorly. Umbos moderately high and projecting forward. Beak sculpture of two or three elevated ridges. Shell smooth, a broad shallow sulcus present in front of the posterior ridge. Periostracum dark brown or chestnut, juveniles often lighter and marked with green rays, particularly near the beaks. Length to 4 inches (10.2 cm).
Pseudocardinal teeth well developed; two in the left valve, one in the right. Lateral teeth straight to slightly curved. Beak cavity very deep. Nacre variable, usually white, occasionally pink or rose-colored in some individuals.
Habitat: Medium to large rivers in sand or gravel in areas with moderate flow.
Status: Widespread but sporadic in the Ohio River and its tributaries. Endangered in Ohio. Species of Special Concern in Illinois and Indiana.