Illinois Natural History Survey - University of Illinois

Amblema plicata (Say, 1817)

Threeridge


 

Amblema plicata, INHS 9062
Amblema plicata, INHS 9062. Spoon River, Fulton County, Illinois.
Length: 4.2 inches (10.7 cm).

Other common names Blue-point, purple-tip, fluter.

Key characters Elongate or rounded shell with ridges or folds on the posterior half. No sculpturing on the anterior end, especially near the umbo.

Similar species Washboardrock-pocketbook.

Description Shell thick, elongate or rounded, and compressed to inflated. Anterior end rounded, posterior end rounded or bluntly pointed. Dorsal margin straight, ventral margin straight to curved. Umbos low, equal to or slightly elevated above the hinge line. Beak sculpture of three or four ridges usually seen only in young shells. Shell smooth on the anterior third, with three or more roughly parallel ridges or folds on the posterior two-thirds. Shells from large rivers generally more inflated and without as many folds or wrinkles as those found in smaller streams. Periostracum yellowish green, light brown, or green in juveniles, becoming dark green, brown, or black in older shells. Length to 7 inches (17.8 cm).Amblema plicata distribution

Pseudocardinal teeth serrated and well developed; two in the left valve, one in the right (occasionally with a small tooth on either side). Lateral teeth serrated and straight to slightly curved; two in the left valve, one in the right. Beak cavity medium to deep. Nacre pearly white, frequently stained, iridescent posteriorly. Some individuals with a purple tint on the posterior end.

Habitat Small to large rivers and impoundments in mud, sand, or gravel.

Status Widespread and common throughout most of its range. Apparently declining in some smaller streams. Commercial species.


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