Sea urchins are small, globular, spiny sea creatures, composing most of class Echinoiea. 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. Otters, wolf eels, and other predators feed on urchins. Sea urchins are harvested and served as a delicacy.