Sea urchins () are spiny, globular echinoderms in the class echinoidea. about 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone — from the intertidal seashore down to 5,000 metres (16,000 ft; 2,700 fathoms). the spherical, hard shells (tests) of sea urchins are round and spiny, ranging in diameter from 3 to 10 cm (1 to 4 in). sea urchins move slowly, crawling with tube feet, and also propel themselves with their spines. although algae are the primary diet, sea urchins also eat slow-moving (sessile) animals. in the food chain, the predators who eat sea urchins are the sea otter and the starfish, the wolf eel, the triggerfish, and human beings. adult s...

Source: Wikipedia