Eccentric Sand Dollar (Dendraster excentricus)

Description: The shells of eccentric sand dollars that are no longer living are often found along shorelines. These shells are white or gray and smooth, while living eccentric sand dollars are gray to purple with almost a felt coating and covered in little hair-like spines (only about 2 mm in length). Sand dollars are echinoderms and they use these spines to burrow, eat, and move. The star-shaped pattern on top of eccentric sand dollars is off-center (their species name excentricus means “off-center”). In this star-shaped pattern are little holes from which specialized tube feet emerge from in order to breathe. The diameter of these sand dollars can be up to 10 cm.

Habitat: These sand dollars are found in the intertidal and subtidal zones, typically in sandy areas. The ones living in the intertidal zone will bury underneath the sand when the tide goes out to retain moisture until it returns. As they get older, they tend to move to deeper water, preferring to be between 4 and 12 m deep. At Haystack, being shallower, we often see juvenile sand dollars around our tidepools.

Diet: A sand dollar’s mouth is a little hole located in the middle of its underside. When they lie flat underwater, they feed on detritus and algae. When they are positioned vertically underwater, they catch larvae and diatoms by using their spines and tube feet as well as the water currents.

Tide Pool Tidbits:

• Eccentric sand dollars live in aggregates - or large groups - underwater and position themselves based on water currents. When they form these groups, they either lie flat or stick up out of the ground sideways, partially buried. They may even swallow sand to help weigh themselves down.

• Predators of sand dollars include crabs, sea stars, and various fishes.

• These sand dollars don’t reach sexual maturity until they’re 4 years old.

• The life span of eccentric sand dollars is, on average, 10 years old.

References: Animal Diversity Web