Sea urchins or urchins are small, spiny, globular animals which, with their close kin, such as sand dollars and constitute the class Echinoidea of the echinoderm phylum. They inhabit all oceans. Their shell, or “test”, is round and spiny and typically from 3 to 10 centimetres (1.2 to 3.9 in) across. Common colors include black and dull shades of green, olive, brown, purple and red. They move slowly and feeding mostly ON algae. Sea otters, wolf eels, triggerfish and other predators feed ON them. Humans harvest them and serve their roe as a delicacy. The name urchin is an old name for the round spiny hedgehogs that sea urchins resemble. In Japan, sea urchin is known as uni (sea urchin) and can retail for as much as $450/kg.; it is served raw as sashimi or in sushi and with soy sauce and wasabi. Japan imports large quantities from the United States, South Korea and other producers. Japanese demand for sea urchin corals has raised concerns about overfishing.