Sand Dollar Echinodiscus auritus
Sand dollars are sea urchins that have become extremely flattened as an adaptation for burrowing through sand. A mat of very fine spines covers the shell, or test, and the pattern of the animal’s skeleton plates can often be seen through the skin. The sand dollar's mouth is on the underside. At the rear are two notches that open at the margins of the test, and water currents passing through these slits are thought to help to push the urchin down and prevent it being swept away.
- Class Echinoidea
- Diameter Up to 4 in (11 cm)
- Depth 0–165 ft (0–50 m)
- Habitat Clean sand
- Distribution Tropical and warm waters of Indian Ocean, Red Sea, western Pacific