Sea urchins are small, spiny, globular animals. They inhabit all oceans. Their shell, is round and spiny, typically from 3 to 10 centimetres across. Common colors include black and dull shades of green, olive, brown, purple, and red. They move slowly, feeding mostly on algae. There anemy is triggerfish, sea otters and some eels.
The lower half of a sea urchin’s body is referred to as the oral surface, (the mouth). While the upper half is the aboral surface, (bom).
The spines, long and sharp in some species, protect the urchin from predators. The spines inflict a painful wound when they penetrate human skin, but are not dangerous.
Sea urchins are dioecious, having separate male and female sexes, although there is generally no easy way to distinguish the two, except for their location on the sea bottom. Males generally choose an elevated and exposed location so that their milt can be broadcast by sea currents. Females generally choose a low-lying location in sea bottom crevices, presumably so that the tiny larvae can have better protection from predators.