Winged Mapleleaf

(Quadrula fragosa) Conrad, 1835
A Winged Mapleleaf mussel

K.S. Cummings, Illinois Natural History Survey

Other Common Names:
False mapleleaf; Hickorynut shell.
Medium to large rivers in mud, sand, or gravel.
Up to 4 inches (10.2 cm).
Outer Shell Color:
Varies. May be yellowish green or light brown. Young mussels may have faint rays.
Inner Shell Color:
White, with iridescent coloring on one end.
Shell Thickness:
Fairly thick.
Shell Outline:
Entire shell outline looks somewhat like an inflated square. The beak(above the point where the two shell halves join), makes up one "corner" of the square. The shell edge closest to the beak is rounded, and the edge farthest away from the beak is squared off.
Shell Surface:
The entire outer surface may look somewhat swollen or bulged-out, and the outer surface is mostly rough. There is a triangular flattened extension of the shell that resembles a wing; running your finger along its outer surface, you will feel many small bumps radiating out. There are two ridges on the outer shell surface, which are made up of many pimple-like bumps. These ridges run from the point where the two shell halves meet to the opposite shell edge. The area between the two ridges is smooth (no pimple-like bumps), and looks slightly pressed-in (it looks similar to the pressed-in mark the length of your finger would make on wet clay).
Scientific Description:
Shell quadrate or square, thick, moderately inflated. Anterior end rounded, posterior end truncated. Dorsal margin straight, ventral margin curved in the anterior half, arched posteriorly. Pronounced ala present posterior to the umbo, with radiating rows of pustules or ridges. Beak sculpture of two raised bumps or nodules that continue downward on the surface of the shell, separated by a sulcus. Periostracum variable. Nacre pearly white, iridescent posteriorly.
Similar Looking Mussels:
Host Fish:
Channel Catfish and Blue Catfish
Only known extant population in the Midwest occurs in Wisconsin.
Minnesota State Listing:
Federal Listing:
Critically endangered.

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