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Mississippi National River and Recreation AreaA 12-spotted skimmer dragonfly perches on twigs while hunting near the Minnesota River.
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Mississippi National River and Recreation Area
Round Pigtoe
(Pleurobema coccineum) Conrad, 1836
A Round Pigtoe mussel
K.S. Cummings, Illinois Natural History Survey
Other Common Names:
Solid pigtoe; Pink pigtoe; Flat pigtoe; Bullnose.
Habitat:
Medium to large rivers in mud, sand, or gravel.
Length:
Up to 4 inches (10.2 cm).
Outer Shell Color:
Variable: Young mussels are greenish brown, light or reddish brown. Older mussels are chestnut or dark brown, sometimes with faint green rays visible near the point where the two shell halves meet.
Inner Shell Color:
Variable: white to pink or rose-colored.
Shell Thickness:
Moderately thick.
Shell Outline:
The overall outline is round, but the edges are somewhat triangular(imagine a triangle blown up, like a balloon). The outline of the shell edge farthest from the beak (which is the swelling above where the two shells join) narrows to a short, blunt point. The shell edge opposite the beak is curved.
Shell Surface:
The outer shell surface is smooth, with no bumps. The entire shells surface can either bulge out or look somewhat flattened. The beak may have two to three raised ridges encircling it.
Scientific Description:
Shell moderately thick, round, and compressed to inflated. Anterior end rounded, posterior end rounded to bluntly pointed. Dorsal margin straight to slightly curved, ventral margin curved. Umbos low. Periostracum smooth, greenish brown light or reddish brown in juveniles, becoming chestnut or dark brown in adults, with faint green rays visible near beaks in some shells. Pseudocardinal teeth well developed: two in left valve, one in right. Lateral teeth straight. Beak cavity shallow to moderately deep. Nacre variable from white to pink or rose-colored.
Similar Looking Mussels:
Ebony Shell; Ohino River Pigtoe, Deertoe, Wabash Pigtoe.
Host Fish:
Spotfin Shiner, Northern Redbelly Dace, Bluntnose Minnow
Distribution:
Widespread but usually uncommon.
Minnesota State Listing:
Threatened.
Federal Listing:
None.
Mussels, One being in a person's hand  

Did You Know?
Under the right conditions, certain freshwater mussel species live for as many as 10 to 100 years. This lifespan is one of the longest for any creature on earth.

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Last Updated: September 20, 2006 at 13:38 EST