Page 40 - The Freshwater Mussels of Oklahoma

Partial Synonymy:
Arkansia wheeleri Ortmann and Walker 1912, Simpson 1914; Isely 1925;
Johnson1980; Branson 1983; Turgeon and others 1988; Howells and
others 1996
Arcidens wheeleri (Ortmann and Walker 1912), Clarke 1981

Description:

“Male and female shells alike. Shell subrotund to subovate or subrhomboidal,
inflated, rather thick and solid; dark reddish-brown or black, usually lighter toward the
beaks, which in young shells are chestnut-colored; epidermis with a silky luster; beaks
very prominent, projecting anteriorly and incurved over the large lunule, their sculpture
consisting of two or three double-looped bars, the loops slightly swollen or tubercular;
sculpture restricted to the extremity of the beaks, the remainder of the umbonal region
being entirely smooth; posterior half of the disk sculptured with irregular, oblique folds,
sometimes nearly obsolete, which on the dorsal slope curve upwards, and in front of the
posterior ridge are crossed by numerous, irregular, radiating, small folds or wrinkles at
right angles to the lines of growth; anterior portion of the disk smooth; anterior margin
nearly straight in front of the beaks, then projecting in a regular curve, which continues
around the basal margin until it meets the posterior margin at an obtuse angle about one-
third up from the base; Hinge margin nearly straight; posterior margin slightly curved;
posterior ridge not prominent, usually rounded, but sometimes obscurely biangulate;
hinge complete; pseudocardinals strong, ragged, in the left valve, two, not strongly
differentiated and coalescing along the hinge line, the anterior narrow and parallel with
the hinge line, the posterior somewhat wider and heavier and scarcely separated from a
strong projection of the interdentum, which is continuous with the lower lateral and
slopes gradually to its extremity; upper lateral low, the groove between them deep and
extending nearly to the beak; a single, strong pseudocardinal in the right valve with a
deep pit behind it to receive the anterior pseudocardinal of the left valve, interdentum cut
away to make room for the interdental projection in the left valve; a single strong, but
rather short lateral; ligament dark brown; muscle scars not very deep, those of the
anterior adductor and posterior adductor large, those of the anterior retractor and pedal
protractor rather small and inconspicuous; Cavity of the beaks very deep; nacre usually
salmon-colored above the pallial line, bluish-white below (sometimes entirely white) and
rather thin, slightly iridescent with a wide, dark prismatic border” (Ortmann and Walker
1912, p98-99).
Comments:
Considered rare and endangered on the Federal and State level. Small
populations confined to parts of Arkansas (mostly extirpated), the Kiamichi River and
Little River in Oklahoma and possibly small tributaries of the Red River in Northeast
Texas.

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