Illinois Natural History Survey - University of Illinois

Alasmidonta viridis (Rafinesque, 1820)

Slippershell mussel

Alasmidonta viridis, INHS 7866. Baker Creek, Kankakee County, Illinois. 
Length: 1.4 inches (3.6 cm).

Other common names None.

Key characters Small, somewhat rectangular shell, high posterior ridge, wavy green rays on posterior half of the

shell, poorly developed lateral teeth.

Similar species Elktoe.

Description Shell small (usually about an inch), somewhat inflated, thin in young individuals to moderately thick in adults. Anterior end rounded, posterior end squared or truncated. Posterior ridge high and rounded, posterior slope flattened. Ventral margin straight or slightly arched. Umbos full and elevated above the hinge line. Beak sculpture of three or four elevated ridges or loops. Shell smooth to rough and yellowish green with numerous wavy green rays, particularly on the posterior half of the shell. Length to 1.5 inches (3.8 cm).

Pseudocardinal teeth triangular; two in the left valve, one in the right. Lateral teeth poorly developed, generally appearing as a slight swelling along the hinge line. Beak cavity moderately deep. Nacre white, iridescent on the posterior third of the shell.

Habitat Creeks and the headwaters of large rivers in sand, mud, or fine gravel.

Status Endangered in Illinois and Iowa. Threatened in Wisconsin.

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