Echinarachnius parma

Echinarachnius parma, the common sand dollar, is a species of sand dollar native to the Northern Hemisphere.


 * Subspecies:
 * Echinarachnius parma obesus H.L. Clark, 1914
 * Echinarachnius parma parma (Lamarck, 1816)
 * Echinarachnius parma sakkalinensis Argamakowa, 1934

Distribution
It is found in the North Pacific and Northwest Atlantic, on the North American east coast from New Jersey north, as well as in Alaska, Siberia, British Columbia, and Japan. It inhabits isolated areas on sandy bottoms below the low tide level down to a depth of 5000 ft.

Description
The tests (shells) of these sand dollars are round, flat and disc-like, typically measuring 3 in in diameter. The entire shell is also covered with maroon-colored moveable spines. The color is a purplish brown, becoming bleached white when washed ashore. As in other echinoderms, five radial furrows branch from the mouth on the animal's underside.

This and other species of Echinarachnius have been around since the Pliocene epoch.