The sand dollar often captivates beachgoers with its distinctive, flattened form. Its common name sparks curiosity, leading many to wonder about its origins. This article explores the sand dollar’s biological nature and unravels why it bears a name conjuring images of both the ocean floor and currency.
Defining the Sand Dollar
The sand dollar is a flattened sea urchin, scientifically classified as an echinoid, belonging to the order Clypeasteroida. These marine invertebrates are relatives of sea stars and sea cucumbers, all sharing a characteristic five-part radial symmetry. A living sand dollar appears quite different from the bleached white disk commonly found on beaches; it is typically covered in a velvety layer of tiny spines, ranging in color from green, blue, violet, or purple, depending on the species.
These small, flexible spines are covered with even tinier hair-like structures called cilia. The familiar white object is actually the sand dollar’s rigid skeleton, known as a test, composed of calcium carbonate. This test only becomes visible after the animal dies, its spines fall off, and the sun bleaches it white.
The “Sand” in Sand Dollar
The “sand” in sand dollar refers to the creature’s preferred environment and behavior. Sand dollars typically inhabit sandy or muddy ocean floors in shallow coastal waters, though some species can be found at greater depths. Their flattened, disc-shaped bodies and specialized spines allow them to burrow efficiently into the sediment.
This burrowing ability helps them find shelter from predators and strong currents. They often remain partially or fully buried, using their spines and cilia to move across the seabed and gather microscopic food particles from the sand. Their coloration when alive also provides camouflage within their sandy habitat, making them difficult to spot until washed ashore.
The “Dollar” in Sand Dollar
The “dollar” component of the name stems from the striking resemblance of the sand dollar’s bleached test to a coin. When washed ashore, the dead sand dollar’s smooth, circular, and flattened skeleton, often bleached white by sunlight, strongly evokes the appearance of a large, silver coin. Historically, beachcombers associated these marine finds with old silver currency, such as the Spanish or American dollar coins.
These coins, particularly the old Spanish dollar or “piece of eight,” had a substantial diameter, making the comparison to the typically 5 to 10 cm (2 to 4 inches) sand dollar quite apt. Beyond the physical resemblance, various folklore and legends have reinforced the “dollar” association. Some tales suggest sand dollars are coins lost by mermaids or currency from the mythical city of Atlantis. The distinct five-pointed petal pattern on the test, along with the five small, dove-shaped jaw parts found inside when broken, have also contributed to symbolic interpretations.