Cyclonaias tuberculata (Rafinesque, 1820)
Other common names: Missouri mapleleaf, purple pimpleback, deerhorn.
Key characters: Rounded shell with a fairly prominent wing, beak covered with fine wavy sculpturing, no green stripe on the umbo, purple nacre. Deep and compressed beak cavity.
Description: Shell round, moderately thick, and compressed to moderately inflated (large rivers). Anterior end rounded, posterior end somewhat squared off. Dorsal margin straight, a wing present behind the umbo; ventral margin curved. Umbos low, even with, or barely rising above the hinge line. Beak sculpture of numerous wavy ridges covering the surface of the umbo. Shell surface, except the anterior fourth, covered with tubercles, forming small ridges on the dorsal wing. Periostracum yellowish brown or greenish brown in young shells (rarely rayed), becoming dark brown in older shells. Length to 5 inches (12.7 cm).
Pseudocardinal teeth large and well developed; two in the left valve, one in the right (usually with a small tooth on either side). Lateral teeth short, striated, and straight or slightly curved; two in the left valve, one in the right. Beak cavity very deep. Nacre usually deep purple, occasionally white with a purple tinge.
Habitat: Medium to large rivers in gravel or mixed sand and gravel.
Status: Widespread but uncommon in most of the Midwest. Endangered in Wisconsin. Threatened in Iowa. Species of Special Concern in Michigan. Species of Special Interest in Ohio.