Anodonta suborbiculata Say, 1831
Other common names: Heelsplitter.
Key characters: Large, thin, nearly circular shell, double-looped beak sculpture, without teeth.
Similar species: Giant floater, paper pondshell
Description: Shell large, thin, nearly circular, and compressed to slightly inflated in some individuals. Anterior and ventral margins broadly rounded, posterior end bluntly pointed. Dorsal margin flattened and nearly straight. Umbos low, flattened, not raised above the hinge line. Beak sculpture of three or four irregular or broken double-looped ridges. A small wing occasionally present behind the umbo. Shell smooth, shiny, yellow or yellowish green to dark brown, with fine green rays in some individuals. Length to 7 inches (17.8 cm).
Both valves without teeth, hinge line only slightly thickened. Beak cavity large and very shallow. Nacre white or pinkish white and iridescent.
Habitat: Ponds, lakes, or sluggish mud-bottomed pools of creeks and rivers.
Status: Locally abundant in the floodplain lakes, sloughs, and oxbows of the Mississippi and Ohio rivers and their tributaries. Rare in Missouri. Species of Special Interest in Ohio.