Sand Dollars Found in the Sea

There are several different kinds of sand dollars.

Sand dollars are patterned grayish white discs that often wash up on shore along beaches. Although mostly known as a decorative item, sand dollars are actually ocean creatures that live in the sand on the seafloor. These animals are more than just a seashore souvenir; they are a fascinating part of the ecosystem.

Appearance

When they wash up on shore, the dead shell, or test, of the sand dollar is usually gray or white in color, with a star-like pattern on its top. However, when they are alive, sand dollars are covered in tiny spines, which give the creature a purple coloration. On their bottom side, more tiny spines and hairs grow. These spines push food toward the mouth of the sand dollar, which is located in the center of the bottom side of the sand dollar. The spines also allow the sand dollar to move or bury itself.

Habitat

Sand dollars often live in large groups, which makes breeding easier. They usually live in water that is between 30 and 40 feet deep. Sand dollars prefer sandy or muddy areas where they can bury themselves or root themselves into the bottom. This burrowing behavior allows the sand dollars to filter through the sand, looking for food. It also provides shelter and protection from predators.

Diet

Sand dollars sift through the sand on which they rest, searching for any tiny organic particles, such as plankton, that they can eat. The tiny hairs and the mucus coating on the underside of the sand dollar push the food particles up toward the sand dollar's mouth. The sand dollar's small mouth opening contains five teeth-type parts, which allow the sand dollar to chew its food.

Life Cycle

When reproduction occurs, gametes are released into the ocean by the sand dollars. These become free-swimming larvae, which can drift many miles with the current. The swimming larvae will go through several different metamorphoses before taking on the well-known sand dollar appearance. After this transformation into adult life, sand dollars can live between six and 10 years. Growth rings on their exoskeletons help determine a sand dollar's age.

Predators

Sand dollars are well protected by their hard outer skeleton, but some predators do threaten them. Starfish, such as the pink sea star, and some snails prey on sand dollars, as well as other types of fish such as the California sheepshead, ocean pouts, skates and starry flounders.

References

• Gulf of Maine Aquarium; The Common Sand Dollar; Cheryl Page
• Enchanted Learning: Sand Dollar
• Monterey Bay Aquarium: Sand Dollar