Simpsonaias ambigua (Say, 1825)
Salamander mussel
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Simpsonaias 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 papershell, spectaclecase, pondhorn.
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).
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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Created 6/9/95 Last Modified 12/15/97 cam