Illinois Natural History Survey - University of Illinois

Quadrula fragosa (Conrad, 1835)

Winged mapleleaf


Quadrula fragosa, UIMNH Z-3871Quadrula fragosa, UIMNH Z-3871. Kaskaskia River, Washington County, Illinois.
Length: 2.1 inches (5.3 cm).

Other common namesFalse mapleleaf, hickory nut shell.

Key characters Fairly thick shell with well-developed teeth. Squared in outline, an obvious wing behind the umbo with wide radiating ridges. Lateral surface of the shell with two rows of pustules separated by a sulcus or furrow.


Similar species Mapleleafwartyback.

Description Shell quadrate or square, thick, and moderately inflated. Anterior end rounded, posterior end squared or truncated. Dorsal margin straight, ventral margin curved in the anterior half, arched posteriorly. A pronounced wing present posterior to the umbo, with radiating rows of pustules or ridges. Umbos small and elevated above the hinge line. Beak sculpture of two rows of raised bumps or nodules that continue downward on the surface of the shell, separated by a furrow or sulcus. Periostracum variable, from yellowis

Quadrula fragosa distribution


Pseudocardinal teeth well developed, serrated; two in the left valve, one in the right. Lateral teeth striated, fairly long, and straight; two in the left valve, one in the right. Beak cavity very deep. Nacre pearly white, iridescent posteriorly.h green to light brown with faint rays in small shells, becoming greenish brown, chestnut, or dark brown in larger individuals. Length to 4 inches (10.2 cm).

Habitat Medium to large rivers in mud, sand, or gravel.

Status Federally Endangered. Only known extant population in the Midwest occurs in Wisconsin.



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