Illinois Natural History Survey - University of Illinois

Anodonta suborbiculata Say, 1831

Flat floater


 Anodonta suborbiculata, INHS 7854
Anodonta suborbiculata, INHS 7854. Mississippi River, Randolph County, Illinois. 
Length: 5.0 inches (12.7 cm).

Other common names Heelsplitter.

Key characters Large, thin, nearly circular shell, double-looped beak sculpture, without teeth.


Similar species Giant floaterpaper 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. Anodonta suborbiculata distribution

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.

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