Illinois Natural History Survey - University of Illinois

Simpsonaias ambigua (Say, 1825)

Salamander mussel


Simpsonaias ambigua, UIMNH Z-3838Simpsonaias ambigua, UIMNH Z-3838. Kankakee River, Will County, Illinois. 
Length: 1.8 inches (4.6 cm).

Other common names Simpson's shell, smooth minishell.

Key characters Small, thin, elliptical shell, poorly developed teeth, double-looped beak sculpture, rayless.

Similar species Cylindrical papershellspectaclecasepondhorn.

Description Shell small, thin, elongate elliptical or oval, and compressed (male) to slightly inflated posteriorly (female). Anterior and posterior ends rounded. Posterior ridge rounded. Dorsal and ventral margins straight, parallel. Umbos slightly elevated above the hinge line. Beak sculpture of three or four double-looped bars. Shell smooth, dull, yellowish tan to dark brown, and rayless. Length to 2 inches (5.1 cm).<em>Simpsonaias ambigua</em> distribution

Pseudocardinal teeth very small, low, rounded; one in each valve. Lateral teeth absent. Beak cavity shallow. Nacre bluish white, occasionally tinged with salmon near the beaks, iridescent on the posterior half.

Habitat Medium to large rivers on mud or gravel bars and under flat slabs or stones.

Status Federal Candidate (Category 2). Endangered in Illinois, Michigan, and Missouri. Threatened in Wisconsin. Species of Special Concern in Indiana. Species of Special Interest in Ohio.

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