This Is How a Sand Dollar Lives, Before You Find It Dead on the Beach
by Owen James Burke
Above: An artist’s liberal interpretation of the colorful sand dollar in life (Echinarachnius parma). No, they don’t look like this, either. Image via acnl.wikia
Sand dollars, or burrowing sea urchins, those white or beige calcified shells, or “tests”, as they’re sometimes called, which you sometimes find along the beach — whole, if you’re lucky — look a lot different in life than they do in death. Like other echinoderms (starfish, brittle stars and other sea urchins), they range widely in color, and like the rest of the sea urchin species, they’re covered in spines, so you wouldn’t want to plant your hand into a live one.
Above: A live sand dollar. Photo: D. Gordon E. Robertson
Their spines work like hundreds of feet and legs with pincers and cilia, or small hair-like fibers, which allow them to crawl, burrow and hunt. Lying in the intertidal zone (between high and low tide) below heavy currents and standing on edge is more slack waters, these coin-shaped echinoderms pick their food out of the water column, which mostly consists of plankton, which they ingeniously store in a small teepee-shaped cone of spines for later consumption. Juvenile sand dollars consume grains of sand like diving weights, so as to not be swept away while feeding in more active currents. When a sand dollar’s stomach grows empty, they pass along a serving of crab larvae or amphipods — whatever they’ve got in stock — spine over spine and down into the mouth, which sits on the underside of their body.
Another little known fact about the sand dollar is that it has teeth, or jaws, at least. This contraption is known by some as “Aristotle’s Lantern,” or to the more biblically-affiliated mind, the “star of Bethlehem.” When you pick one up on the beach and hear it a rattle, it’s usually the teeth, also referred to as the “doves of peace.” Next time you find a shattered test on the beach, crack it open and you might find what look a bit like shark teeth. But moreover, the next time you’re fortunate enough to lift an intact one of these little medallions off the beach, don’t just appreciate its beauty in death; take a moment to imagine the life it once lived.
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