Urchin is an old name for hedgehogs. So Sea urchins are the hedgehogs of the sea. Sea urchin is an Echinoderm and lives on the sea bed to a depth of 5000 m. Its globe-shaped body has very long movable spines. Some species walk on their spines while others use their tube feet for locomotion. Contact with the spines is quite painful. However, relatively few species are venomous. Ancient philosopher Aristotle discovered a masticatory apparatus, to which five teeth are attached inside the mouth. It is called Aristotle’s lantern.
The gonads of both male and female sea urchins are taken as a delicacy in Mediterranean countries, Japan, New Zealand and West Indies. It is usually called sea urchin roe or corals. One interesting fact about their life is that they are sessile at birth that means they are fixed to a substrate at juvenile stage of their life.