Sea Urchin

The mouth of the urchin is on the bottom (oral) part of the test. Food is chewed by 5 teeth which are part of a complex mechanism called Aristotle’s lantern. The chewed food then moves through the esophagus, stomach, and then intestine. When food enters the intestine and forms round pellets which are later excreted through the anus, which is at the top (aboral) side of the test.

Red sea urchin larvae feed on microorganisms using cilia to sweep them into their mouths. As juveniles, sea urchins feed on diatoms and smaller food. Adults feed primarily on kelp (especially Nereocystis or Macrocystis) but can eat sessile invertebrates. Often forms large subtidal aggregations in or near kelp beds.
During reproduction, red sea urchins aggregate together.