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Purple sea urchin

Strongylocentrotus purpuratus

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Fun Facts

The sea otter is one of the main natural predators that eats sea urchins. Because sea otters are endangered, urchins have increased in numbers and reduced the amount of kelp growing in some places. 

Species Type:

Invertebrates

Common Name(s):

Purple sea urchin

Size:

They can be 2–4 inches (5–10 centimeters) across.

Diet:

These urchins graze on algae, including giant kelp.

Range & Habitat:

Purple sea urchins live rocky intertidal areas and kelp beds in the Eastern Pacific Ocean from Alaska down to Cedros Island, Mexico.

Details:

This urchin has a round body covered with purple spines. Each spine is attached by a ball-and-socket joint, allowing the urchin to move them in different directions. They actively attach algae, shells, and rocks to themselves, possibly for UV protection and camouflage. In areas where predators are lacking, urchins can destroy entire kelp forests by overgrazing. Their unique mouth structure, called Aristotle’s lantern, contains five strong teeth that can even bore into rock.