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The sand dollar is a marine invertebrate animal, closely related to the starfish, sea lily, the sea cucumber and the sea urchin. Sand dollars come from the Echinoids class, which means "spiny skinned creature."

The legend of the sand dollar first began in Maine, where children were taught to believe that sand dollars are pressed sand or that they are the money mermaids use. Because sand dollars are mostly found already deceased on sandy beaches, many don't realize that the sand dollar is a living, breathing creature. As early as the 17th Century, the sand dollar was sold as a trinket and advertised not as a living animal, but rather, as tokens to beach goers.

Though few ever see the sand dollar alive, they are beautiful, colorful creatures, outfitted with a maroon colored jacket of moving spines. A semi pliable shell covers the sand dollar's tiny body, within which lies five sets of pores arranged in a petal-type pattern. Each pore is used to move water into its internal vascular system, which allows for movement.

Sand dollars live on top of or just beneath the surface of sandy or muddy areas. The sand dollar has a rigid, flat, disk-shaped shell or "test." Flattened spines on the underside of the animals allow it to slowly creep through sand or burrow itself deep within sand. The fine, tubed feet of the sand dollar are similar to several other species in the echinoderm family. Tubed feet are used for respiration. Fine, thin cilia cover the tiny spines of the sand dollar, and in combination with a sticky, mucous coating, aid in moving food to the mouth. Much like its close cousin the starfish, the sand dollar's stomach and mouth are located on the underside of the animal. Sand dollars exist on a diet of plankters and organic particles.

Thanks to their hard skeleton and very small body, there are few animals that stop to bother with the sand dollar. The Ocean Pout, an eel like fish, is the only known species that actively hunts the sand dollar in its natural environment.

Sand dollars measure 2-4 inches in diameter and are found throughout the world, with the exception of Europe and Antarctica. Together, the starfish and sand dollar are among the most highly populated species of marine life.

Sand dollars are very often found together on the ocean floor. Not only do the melted away layers of sand make it a comfortable place to live, but it's also convenient for reproduction. During reproduction periods, gametes are released into the water, as is with most echinoids. The swimming larvae then metamorphose through several stages before their hard overcoating begins to form.

In recent years, several organizations have taken up the plight of the sand dollar, educating beach combers of the significant ecological value the sand dollar holds. Many rescue teams pull dying sand dollars from the sand at high tide and throw them back out to sea. Today, almost all beaches request the same.