Sand dollars, like all members of the order Clypeasteroida, possess a rigid skeleton known as a test. The test consists of calcium carbonate plates arranged in a fivefold radial pattern. In living individuals the test is covered by a skin of velvet-textured spines; these spines are in turn covered with very small hairs (cilia). Coordinated movements of the spines enable sand dollars to move across the seabed.

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Photo credit: © ART Collection / Alamy / Afripics
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Keywords: 18-270mm, art, beach, cockles, dollars, image, photo, photograpgh, pzd, sand, scallops, sea, shells, tamron