Western sand dollar

Dendraster excentricus

ORDER

Scutellina

FAMILY Dendrasteridae

TAXONOMY

Dendraster excentricus Eschscholtz, 1831.

OTHER COMMON NAMES English: Eccentric sand dollar.

PHYSICAL CHARACTERISTICS

Rigid test measuring up to 3.5 in (9 cm) and covered with moveable spines. Pale gray-lavender to dark purplish black coloration; characteristic pentaradiate or petal-shaped pattern tube feet on upper surface of test.

DISTRIBUTION

Northeastern coasts of the Pacific ocean from southern Alaska to Mexico. Found in depths between 130-295 ft (40-90 m).

HABITAT

Inhabits sandy bottoms within sheltered bays, lagoons, and open coastal areas. Commonly found in dense aggregations forming a carpet of animals.

BEHAVIOR

Occurs in large numbers on the seabed. These high densities are thought to help influence the nature of near-bed currents to assist in feeding.

FEEDING ECOLOGY AND DIET

The only echinoid to suspension feed, trapping suspended organic particles as they drift in passing water currents. Mucus strands assist in trapping organic matter. Juveniles ingest sand when feeding to act as ballast. Stand in the sand obliquely when feeding and use their tube feet for respiration and catching food.

REPRODUCTIVE BIOLOGY

Sexual reproduction; spawning period between July and August. Adults may feed on larvae, but not their eggs because of a protective coating. Settling larvae have a greater protection from predators if they settle within existing sand dollar beds. Estimated lifespan is up to 15 years.

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