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Sea Urchins and Sand Dollars: Echinoidea

Behavior And Reproduction

Sea urchins move slowly and usually search for food at night to avoid predators. They use their teeth to bite and scrape their food. Sand dollars sift the sand for food while burrowing. Their spines are dense enough to prevent sand grains from falling through yet are fine enough to allow food particles to drop out onto strings of mucus before being placed in the mouth. Sea urchins and sand dollars use their tube feet for trapping food particles, for movement, for prey capture, for attaching to the material they live on, and for breathing.

Sea urchins and sand dollars have separate sexes. Females release millions of eggs into the water, where they unite with sperm from the males and develop into larvae. Larvae (LAR-vee) are animals in an early stage that change form before becoming adults. Sea urchin and sand dollar larvae drift before settling to the bottom and transforming into young animals with a body form that looks like that of adults. In a few species of sea urchins and sand dollars the young develop inside the females. These species do not have free-floating larvae.


On wave-exposed shores, sea urchins group together and interlock spines with one another, thus reducing the risk of being swept away by strong waves.

Additional topics

Animal Life ResourceJellyfish, Sponges, and Other Simple AnimalsSea Urchins and Sand Dollars: Echinoidea - Physical Characteristics, Behavior And Reproduction, Sea Urchins, Sand Dollars, And People, Long-spined Sea Urchin (diadema Savignyi): Species Accounts - GEOGRAPHIC RANGE, HABITAT, DIET, CONSERVATION STATUS