Sand dollars got their name because their flat, round shape is similar to coins. In ancient times, some believed they were coins used by mermaids. Like gold and silver coins from a sunken treasure chest, sand dollars wash ashore to delight beach combers. In South Africa they are known as pansy shells because the five rounded shapes on their surface resemble pansy flowers. In Australia and New Zealand, they are known as sea biscuits or sea cookies.
But what are they exactly? What kind of creature lived in these beautiful shells with their distinctive design? Sand dollars are actually the skeletons of a species of flat sea urchins. They belong to the Clypeasteroida order, and are related to starfish and sea cucumbers. Sand dollars live in both the Atlantic and Pacific Oceans, in the temperate and tropical regions of each.
While alive in the ocean, sand dollars are not white. They are covered with fine, velvety spines in shades of blue and purple. The colorful spines cover the distinctive five-point design that makes them so instantly recognizable when they wash up on the beach. They use the tiny hairs on these spines to move across the ocean floor, burrow into the sand and move food to their mouths.
How to find sand dollars?
Sand dollars are quirky creatures. They live in the sand at the floor of the sea, and when the water is tranquil, they stand on their sides with an edge buried in the sand. When the water grows too rough for this position, they flatten themselves on the sand or burrow into it. Adults can grow heavier skeletons in water with a fast current, while young sand dollars swallow sand to weigh themselves down.
They eat larvae, algae and other tiny organisms. When sand dollars are in their larvae stage, they look nothing like adults. Instead, they have six little arm-like limbs. But they can’t swim fast, which makes them vulnerable to hungry fish. Their response to predators is both amazing and bizarre. They clone themselves. The tiny larvae grows an even tinier little bud that splits off to form a duplicate, which researchers have discovered is genetically identical to the original. Other sea creatures do clone themselves, but usually when they find good living conditions. The cloning does not really help them escape the predatory fish, but it is apparently a reaction to them.