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An diagram of the anatomy of a sea urchin. Sea urchins are small, globular, spiny sea creatures, composing most of class Echinoidea. They are found in oceans all over the world. Their shell, or "test", is round and spiny, typically from 3 to 10 cm across. Common colors include black and dull shades of green, olive, brown, purple, and red. They move slowly, feeding mostly on algae. Sea otters, wolf eels, and other predators feed on urchins. Sea urchins are harvested and served as a delicacy.

Sea Urchin

An diagram of the anatomy of a sea urchin. Sea urchins are small, globular, spiny sea creatures, composing…

An illustration of various sea urchin fossils. "1, Palaeechinus; Carboniferous; 2, A plate and radiole of Archaeolcidaris; 3, A radiole of Cidaris; Jurassic; 4, Hemicidaris; Mid. Jurassic; 5, Salenia; Cretaceous; 6, Dyaster; Jurassic; 7, Enallaster; Cretaceous; 8, Catopygus; Cretaceous." -Britannica, 1910

Sea Urchin Fossils

An illustration of various sea urchin fossils. "1, Palaeechinus; Carboniferous; 2, A plate and radiole…