Potamilus purpuratus (Lamarck, 1819)
Other common names: Blooper, blue mucket, blue hen, purple pocketbook.
Key characters: An elongate and rectangular shell, inflated, dark green to black, with a purple or pink nacre.
Similar species: Pink heelsplitter.
Description: Shell rectangular, moderately to greatly inflated, thin in young to moderately thick in older individuals. Anterior end rounded, posterior end bluntly squared or truncated. Umbos flattened, only slightly elevated above the hinge line. A low wing may be present behind the umbo. Beak sculpture of three or four double-looped ridges, visible only in young shells. Shell smooth, brown, becoming black in old individuals. Young mussels typically marked with dark green rays that become fainter with age. Length to 8 inches (20.3 cm).
Pseudocardinal teeth small, roughened and divergent; two in the left valve, two in the right. Lateral teeth long, thin, and curved. Beak cavity shallow. Nacre deep purple and highly iridescent.
Habitat: Large rivers in mud or mixed mud and gravel.
Status: A southern species rarely found above the confluence of the Mississippi and Ohio rivers. Species of Special Concern in Illinois.