Illinois Natural History Survey - University of Illinois

Obliquaria reflexa Rafinesque, 1820

Threehorn wartyback


Obliquaria reflexa, INHS 3052


Obliquaria reflexa, INHS 3052. Rock River, Rock Island County, Illinois. 
Length: 2.2 inches (5.6 cm).

Other common names Hornyback, three dot, three knot.

Key characters The large knobs that alternate from side to side will distinguish this mussel from all other species found in the Midwest.


Similar species Pimplebacksheepnosetubercled blossom.

Description Shell usually small, rounded, moderately thick, and inflated. Anterior end rounded, posterior end bluntly pointed. A row of three or four large, elevated knobs extending from the beak to the center of the ventral margin, with the knobs alternating in position with those of the other side. Often a broad depression present between the knobs. Beaks elevated and curved inward. Periostracum highly variable in color from light yellowish brown to green and dark brown. Shell usually covered with numerous fine, dark green, broken rays. Length to 3 inches (7.6 cm).

Pseudocardinal teeth heavy and serrated; two in the left valve, one in the right. Lateral teeth straight to slightly curved, short, and serrated. Beak cavity shallow to moderately deep. Nacre pearly white.

Habitat Large rivers in sand or gravel; may be locally abundant in impoundments.

Status Widespread and common in the large rivers of the Midwest. Threatened in Ohio.

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