Megalonaias nervosa shell description:

 “Shell long rhomboid or long quadrate [sic.], subinflated to inflated, solid, inequilateral; posterior ridge usually full, rounded; beaks rather full and high, their sculpture strong, doubly looped or zigzag ridges; dorsal line straight or lightly curved; anterior end rounded, generally angled above; base line straight or a little curved; posterior end almost squarely or somewhat obliquely truncate and angled above where it joins the low dorsal wing, rounded below; surface with uneven, concentric sculpture, all except where it joins the low dorsal wing, rounded below; surface with uneven, concentric sculpture, all except the anterior basal part, more or less covered with oblique folds and nodules.  The earlier growth is usually densely covered with subradial or chevron-shaped, nodulous plications; frequently the sculpture in front is decidedly nodulous; epidermis brownish or blackish; pseudocardinals elevated, radial, radially striate; laterals straight or slightly curved; muscle scars large, the anterior ones with rough nacreous matter; beak cavities deep, compressed; nacre whitish, often blotched with lurid color, much thinner and iridescent behind; pallial line remote ”(Simpson, 2014; Mather, 2007).