Illinois Natural History Survey - University of Illinois

Megalonaias nervosa (Rafinesque, 1820)



Megalonaias nervosa, INHS 12568. East Fork White River, Lawrence County, Indiana. 
Length: 5.0 inches (12.7 cm).

Other common names Bald-pate, board.

Key characters Large, black shell, heavily sculptured with V-shaped ridges in the front and large folds on the sides and back, particularly in smaller shells.Megalonaias nervosa distribution





Similar species Threeridgerock-pocketbook.

Description Shell large, thick, slightly elongate, rectangular, and compressed to moderately inflated. Anterior end rounded, posterior end truncated. Dorsal margin straight, ventral margin straight to slightly curved. A small wing with several ridges present behind the umbo (most evident in small shells, becoming indistinct in larger shells). Umbos not elevated above the hinge line. Beak sculpture of prominent double-looped ridges, enlarging into bumps and folds on the posterior ridge. Upper shell with irregularly shaped tubercles or V-shaped ridges (covering the shell of juveniles). A series of large folds present on the posterior half of the shell. Periostracum rayless, light brown in juveniles, dark brown or black in adults. Length to 11 inches (27.9 cm).

Pseudocardinal teeth well developed and serrated; two in the left valve, one in the right (occasionally with a small tooth on either side). Lateral teeth straight to slightly curved; two in the left, one in the right. Beak cavity fairly deep. Nacre white, often with purple or copper-colored blotches, iridescent posteriorly.

Habitat Primarily large rivers with a good current; occasionally medium-sized streams in mud, sand, or gravel.

Status Commercial species. May be common in its preferred habitat. Endangered in Ohio.


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