Pyganodon grandis

Pyganodon grandis, the giant floater, is a species of freshwater mussel, an aquatic bivalve mollusk in the family Unionidae, the river mussels. This species is fast-growing, large, and has a short lifespan. It is variable and widespread across the United States and southeastern Canada.

Original description (Say 1829): "Shell very large, subovate; disk unequally wrinkled and undulated transversely, dark yellowish brown; umbo elevated; beak slightly elevated, with generally, two or three small sinuous, acute undulations; hinge margin slightly arquated, sometimes nearly rectilinear, somewhat angulated at its anterior termination, thence the edge descends by a nearly rectilinear, or slightly concave line to the anterior margin, which is considerably narrowed; sinus of the hinge margin concave; posterior margin widely rounded; within white margined, particularly before, with dusky."