Sea Urchins and Sand Dollars: Echinoidea

Physical characteristics: Western sand dollars have a rigid shell about 3.5 inches (9 centimeters) across and covered with moveable spines. These sand dollars are pale grayish lavender to dark purplish black. They have a five-way petal-shaped pattern of tube feet on the upper surface of the shell.

Geographic range: Western sand dollars live along the west coast of North America from southern Alaska to Mexico.

Habitat: Western sand dollars live on sandy bottoms in sheltered bays, lagoons, and open coastal areas.

Western sand dollars live in groups that form a thick carpet of animals. Scientists believe these sand dollars form the groups to influence the water current so that more food flows toward them. (Illustration by Bruce Worden. Reproduced by permission.)

Diet: Western sand dollars eat plankton, or microscopic plants and animals drifting in water.

Behavior and reproduction: Western sand dollars live in groups that form a thick carpet of animals. Scientists believe these sand dollars form the groups to influence the water current so that more food flows toward them. Mucus strands help the sand dollars trap food particles. Young Western sand dollars take in sand when feeding to help weigh them down.

Western sand dollars release sperm and eggs into the water, where they unite and develop into larvae, which transform into young animals that grow into adults. Some scientists believe adult Western sand dollars eat their larvae but not the eggs, which have a protective coating. Western sand dollars live about fifteen years.

Western sand dollars and people: Western sand dollars are prized by beachcombers and collectors.

Conservation status: Western sand dollars are not considered threatened or endangered. ∎