spines, long and sharp in some species, protect the urchin from predators like sea otters, wolf eels & triggerfish. The spines inflict a painful wound when they penetrate human skin, but are not dangerous. It is not clear if the spines are venomous.
Humans harvest the urchin & serve its roe as a delicacy.
They inhabit all oceans. Their shell is round and spiny. Common colors include black and dull shades of green, olive, brown, purple, and red.
They move slowly, feeding mostly on algae. They have hundreds of tiny, transparent, adhesive "tube feet".
These are sea urchin shells or "tests". Each white band is a location of a row of "tube feet".
This is a sputnik sea urchin shell.