Quadrula pustulosa (Lea, 1831)
Quadrula pustulosa, INHS 11704. Iroquois River, Kankakee County, Illinois.
Other common names Wartyback, warty pigtoe.
Key characters Rounded shell, a green stripe on the umbo, usually densely covered with pustules. Beak cavity deep and open, not compressed as in the purple wartyback.
Description Shell thick, rounded, and compressed to moderately inflated. Anterior end rounded, posterior end rounded to somewhat truncated. Dorsal margin straight, ventral margin curved. Umbos elevated above the hinge line. Beak sculpture, when present, of two or three very small ridges. Shell normally smooth on the anterior half; posterior half or two-thirds covered with pustules or bumps (rarely absent). Periostracum yellowish-green to light brown in small shells, becoming chestnut to dark brown in older shells. A broad, broken green ray present on the umbo extending toward the ventral margin, may be indistinct on older shells. Length to 4 inches (10.2 cm).
Pseudocardinal teeth serrated and well developed; two in the right valve, one in the left (occasionally with a small tooth on either side). Lateral teeth heavy, serrated, and straight to slightly curved; two in the left valve, one in the right. Beak cavity deep. Nacre pearly white, iridescent posteriorly.
Habitat Medium to large rivers in mud, sand, or gravel.
Status Widespread and relatively common. Commercial species.