Sheepnose
Plethobasus cyphyus (Rafinesque, 1820) |
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Sheepnose |
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| Plethobasus cyphyus, INHS 4179. Tippecanoe River, Pulaski County, Indiana. Length: 3.8 inches (9.7 cm).
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| Other common names Bullhead.
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| Key characters Oblong shell with a smooth surface except for a single row of bumps or knobs running from the umbo to the ventral margin.
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| Similar species White wartyback, threehorn wartyback, round pigtoe,
Wabash pigtoe, hickorynut.
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| Description Shell thick, oval or oblong, somewhat elongate, and
slightly inflated. Anterior end rounded, posterior end bluntly pointed. Dorsal
margin straight, ventral margin curved anteriorly, straight posteriorly. Umbos
slightly elevated above the hinge line. Beak sculpture of two heavy ridges,
visible only in young shells. Shell smooth, except for a row of knobs or
tubercles on the center of the valve, running from the umbo to the ventral
margin (some- times obscure). A shallow sulcus or furrow present between the
row of tubercles and the posterior ridge. Periostracum yellow or light brown in
juveniles, becoming chestnut to dark brown in adults. Length to 5 inches (12.7
cm). Pseudocardinal teeth rather small relative to overall shell size; two in the left valve, one in the right (occasionally with a smaller tubercular tooth on either side). Lateral teeth long, straight or slightly curved; two in the left valve, one in the right. Beak cavity shallow. Nacre white, occasionally tinged with pink or salmon.
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| Habitat Medium to large rivers in gravel or mixed sand and gravel.
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Status Rare throughout its range. Endangered in Indiana, Iowa, Ohio,
and Wisconsin. Threatened in Illinois. Rare in Missouri.
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