Lasmigona costata (Rafinesque, 1820)
Other common names: Sand mussel, squawfoot.
Key characters: Elongate, compressed shell with prominent ridges or folds (flutings) on the posterior slope and poorly developed lateral teeth (paired in the left valve).
Similar species: Creek heelsplitter.
Description: Shell elongate, moderately thick, and compressed to slightly inflated. Anterior and posterior ends sharply curved. Dorsal and ventral margins straight. Umbos low, not projecting above the hinge line. Beak sculpture of three or four heavy, more or less double-looped ridges parallel with the hinge line. Prominent sculpturing on the posterior slope consisting of about 10-20 heavy, rounded ridges of folds. Additional surface sculpturing on the lateral surface near the middle of the shell. Periostracum green or yellowish green with numerous green rays in small individuals, becoming chestnut or dark brown in older shells. Length to 7 inches (17.8 cm).
Pseudocardinal teeth thick; two in the left valve, one (occasionally two) in the right. Lateral teeth short and poorly developed, often appearing only as ridges or thickenings of the hinge line. Beak cavity shallow. Nacre white or bluish white and often salmon-colored, particularly in the beak cavities.
Habitat: Medium to large rivers in sand, mud, or fine gravel in areas with slow to moderate flow.
Status: Widespread but relatively uncommon. Endangered in Iowa.