The sand dollar is an invertebrate sea creature; a flat burrowing sea urchin. Their skeletons, called “tests”, are found on beaches worldwide. The test is usually white or grayish-white, with a star-shaped marking in its center.

When they are alive, sand dollars look much different. They are covered with short, velvety spines that are colored somewhere between a deep purplish-brown to purplish-red, depending on the species. Adult animals measure between 2-4 inches (5-10 cm) in diameter and most are approximately 1/3 inch (.85 cm) thick.

Most sand dollars live in seawater, although some species are found in estuaries. As their name suggests, they prefer to live in the sand, where they use their spines to burrow in, in search of protection and food.

Sand dollars are classified as carnivores. Their diet consists of small particles found in the sand, usually microscopic algae, but they will also eat fragments of other animals. The particles land on their spines, and are transported to the sand dollar's mouth (on the underside of the creature) by its tube-like feet and pincers. Some sand dollars are known to rest on their edges in the sand in order to maximize their ability to catch prey drifting or floating by. Lifespan is 8-10 years; the adults have few natural predators, although starfish have been known to eat them occasionally.

After they die, the sun bleaches their color away, turning them into the white, decorative sand dollars that beachcombers know and love.

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