Eccentric Sand Dollar (Dendraster excentricus)

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Coldwater Marine Aquatics recommends you keep these animals in 55F-60F water.


Eccentric sand dollar (Dendraster excentricus), also known as the sea-cake, biscuit-urchin, western sand dollar, or Pacific sand dollar, is a member of the order Clypeasteroida, better known as sand dollars, a species of flattened, burrowing sea urchins found along the Pacific Ocean from Alaska to Baja California.

They are colored gray, brown, black or shades of purple. Their size is variable but up to 100 mm wide, and a dome shaped carapace varying in height to about 10 mm, with a circular body or test. Their body is covered with fine, spiny tube-like feet with cilia, and like other echinoderms they have five-fold radial symmetry. 

Like its cousins, dendraster is a suspension feeder which feeds on crustacean larvae, small copepodsdiatomsplankton, and detritus. Adult sand dollars move mainly by waving their spines, while juveniles use their tube feet. The tube feet along the petalidium are larger and are used for respiration while tube feet elsewhere on the body are smaller and are used for feeding and locomotion. They frequently move around if they are lying flat. When feeding they usually lay at an angle with their anterior end buried and catch small prey and algae with its pedicellariae, tube feet, and spines and pass them to the mouth. Their mouth includes a small Aristotle's lantern structure found in most Echinoids. In high currents adults grow heavier skeletons while juveniles swallow heavy sand grains to keep from being swept away. They will bury themselves when they are being preyed on.

They are either found subtidally in bays or open coastal areas or in the low intertidal zone on sandy on the Northeast Pacific coast. It can live at a depth of 40 to 90 meters, but usually is found in more shallow areas. Sand dollars are usually crowded together over an area half buried in the sand. As many as 625 sand dollars can live in one square yard (0.85 sq m). It is the only sand dollar found in Oregon and Washington.

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