Sea urchins /ÃËÃÅÃÂrtÃÆênz/, are typically spiny, globular animals, echinoderms in the class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal to 5,000 metres 16,000 ft; 2,700 fathoms.[1] Their tests hard shells are round and spiny, typically from 3 to 10 cm 1 to 4 in across. Sea urchins move slowly, crawling with their tube feet, and sometimes pushing themselves with their spines. They feed primarily on algae but also eat slow-moving or sessile animals. Their predators include sea otters, starfish, wolf eels, triggerfish, and humans.
Like other echinoderms, urchins have fivefold symmetry as adults, but their pluteus larvae have bilateral mirror symmetry, indicating that they belong to the Bilateria, the large group of animal phyla that includes chordates, arthropods, annelids and molluscs. They are widely distributed across all the oceans, all climates from tropical to polar, and inhabit marine benthic sea bed habitats from rocky shores to hadal zone depths.
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