Sand dollars are shaped like flattened Sea Urchins. They have tube feet and spines so small and closely packed that the living animal looks and feels like velvet. While alive, Sand Dollars range from gray to charcoal-red and deep purple to almost black. They’re often lighter on the aboral (back) side. Living Sand Dollars are seen less frequently than the familiar tests (shells) which are cast up on the beach and often collected by people. These flattened discs are gray to white with an off-center, five-petal flower pattern on the back.
In quiet waters, sand dollars usually live with the lower portion of their bodies buried in the sand and the upper portion protruding into the current at an angle like a wheel. In rougher water, sand dollars usually lie flat, partially or wholly buried in the sandy floor. When prone or buried, the sand dollar feeds on detritus diatoms and deposits swept by cilia currents toward the mouth. When standing vertically it becomes a suspension feeder catching prey and algae with its spines and tube feet. Sea Stars, fishes and crabs eat Sand Dollars.
Sand Dollars can be found from Alaska to northern Baja California. They live on sandy or sandy-mud bottoms in the low intertidal and subtidal zones in sheltered bays. They also live in deeper waters off the open coast up to 131 feet (40 m).