Sand-dollar definitions

Any of various thin circular echinoderms of the order Clypeasteroida, especially Echinarachnius parma, of coastal northern Atlantic and Pacific waters, having a covering of short movable spines.
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The disklike internal skeleton of a sand dollar, having five radially symmetric oblong markings and often a pattern of long narrow holes.
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Any of an order (Clypeasteroida) of flat, round, disk-shaped echinoid echinoderms that live on sandy ocean beds.
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Any echinoderm of the order Clypeasteroida, having a flat, disk-shaped body with the mouth in a mid-ventral position, and living in sand, on or near the surface.
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