Eccentric Sand Dollar

Overview

The Eccentric Sand Dollar (Dendraster excentricus) is a flattened, burrowing echinoid commonly found along the northeastern Pacific coastline. Unlike regular sea urchins, this species features a distinct, disk-shaped body and is well-known for the off-center, flower-like pattern on its upper surface.

Distribution & habitat

This species ranges from southern Alaska to Baja California, Mexico. They typically inhabit nearshore environments, including open coasts, sandy lagoons, tidal channels, and sheltered inlets. They are often found in dense, organized colonies on fine sand bottoms, where they may partially or fully bury themselves.

Appearance

Adults typically reach up to 10 cm in diameter, though some may grow slightly larger. Their skeleton, or test, is covered in short, movable spines that give the animal a velvety texture and range in color from pale gray-lavender to purplish-black. After death, the test bleaches to a creamy white, revealing the characteristic off-center petaloid pattern on the aboral (top) side.

Biology & behavior

These sand dollars exhibit unique behavioral adaptations to their environment. In high-flow conditions, they often burrow horizontally to avoid displacement, while in calmer waters, they may stand upright in the sediment to maximize exposure to water currents. Adults primarily use their spines for locomotion, whereas juveniles rely on their tube feet. They are suspension feeders, capturing food particles such as diatoms, algae, and detritus from the water column using their spines and cilia. Reproduction occurs via broadcast spawning, typically between July and August.