Illinois Natural History Survey - University of Illinois

Pyganodon (=Anodontagrandis (Say, 1829)

Giant floater


 

Pyganodon grandis, INHS 7854Pyganodon (=Anodonta)grandis, INHS 10319. Lone Tree Creek, Champaign County, Illinois. 
Length: 5.1 inches (13.0 cm).

Other common names Floater, stout floater, papershell, hogshell, slopbucket.

Key characters Large, thin, elongate shell, beaks elevated above hinge, double-looped beak sculpture, without teeth.

Similar species Flat floaterpaper pondshellcreepercylindrical papershell.

Description Shell extremely variable but usually large, somewhat elliptical or elongate, and inflated. Shell extremely thin in young mussels, somewhat thicker in older individuals. Anterior end broadly rounded, posterior end bluntly pointed. Ventral margin straight or slightly curved. Umbos full, usually located in the anterior third of the shell but occasionally more toward the center in the large-river form (P. grandis var. corpulenta), elevated above the hinge line. Beak sculpture of three to five double-looped ridges. Shell smooth, light yellow or yellowish green with rays visible in younger specimens, becoming dark green to brown in older shells. Length to 10 inches (25.4 cm).<em>Pyganodon</em> (=<em>Anodonta</em>) <em>grandis</em> distribution

Valves without teeth, hinge line slightly thickened and curved. Beak cavity broad and shallow. Nacre variable and may be silvery white, cream, pink, salmon, or copper-colored.

Habitat Typically, ponds, lakes, and sluggish mud-bottomed pools of creeks and rivers; can be found in a variety of other habitats as well.

Status Widespread and common.


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