Sand Dollar
Dendraster excentricus

Physical Description

  • When dead, their exoskeleton (hard external body covering) is the most recognizable. It is a small white circle, with a five-point star in the center 
  • When alive, sand dollars are often purple or gray, with densely packed, tiny spines all over their surface, covering the exoskeleton and giving them almost a furry appearance
  • About 3.5 inches across

Range

  • From Alaska to Baja California, Mexico

Habitat

  • Live on the sandy seafloor
  • Intertidal waters to 130 feet depth

Diet

  • Crustacean larvae, small copepods, diatoms, algae, and detritus
  • They use their tiny spines to move food from their body to a central mouth on their bottom side

Predators

  • California sheephead, starry flounders, and large pink sea stars
  • When pink sea stars approach sand dollars, the sand dollars bury themselves in the sand

Interesting Facts

  • In New Zealand, sand dollars are called sea cookies, and in South Africa they are called pansy shells! 
  • In calm waters, sand dollars stand on one end, partially buried in the sand, to catch particles. In rough waters, they lay flat so they don’t get moved by the waves. In fast currents, young sand dollars eat sand to weigh themselves down! 
  • Scientists can age a sand dollar by counting the growth rings on the exoskeleton plates. They can live to be 10 years old.
  • Sand dollars often crowd together, sometimes as many as 625 animals in a square yard. 
  • Sand dollars’ mouths have five teeth-like sections to grind up their food. They can “chew” their food for fifteen minutes before eating, and take two days to digest it. 

Sources: Monterey Bay Aquarium

Photo: David R Andrew

Learn about sand dollars, and other creatures in the sand, in Sandy Shores (Grade 2) at Birch Aquarium.

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