Plethobasus cooperianus (Lea, 1834)
Other common names: Orange-footed pearlymussel.
Key characters: Round shell with pustules only on the posterior three-fourths of the shell. No green ray on the umbo. The live mussel has an orange foot.
Description: Shell thick, solid, round or slightly elongate, and moderately inflated to compressed. Anterior end rounded, posterior end rounded to bluntly pointed. Dorsal margin straight or slightly curved, ventral margin curved. Umbos low, directed forward, and only slightly elevated above the hinge line. Anterior fourth of the shell smooth, numerous pustules present on the posterior three-fourths. Periostracum rayless, light brown in small shells, becoming chestnut or dark brown color in larger individuals. Length to 4 inches (10.2 cm).
Pseudocardinal teeth well developed; two in the left valve, one in the right, with a smaller tooth on either side. Lateral teeth rather short, straight or slightly curved; two in the left valve, one in the right. Beak cavity very deep. Nacre white, usually with pink or salmon near the beak cavity, iridescent posteriorly.
Habitat: Large rivers in gravel or mixed sand and gravel.
Status: Federally Endangered. Still extant in the Ohio River.