Sea urchins, as members of the phylum Echinodermata, are relatives of sea stars and sea cucumbers. They have hundreds of tiny tubelike feet which function in movement, respiration and feeding.
Sea urchins are characterised by their numerous visible spines which make them look very intimidating. They can cause painful wounds but are generally not dangerous. The spines protect the urchins from predators. The spines are typically 1 to 3 cm in length.
The mouth of regular urchins lie in the centre of the oral surface. It is surrounded by soft tissue lips with small bony pieces embedded in it. In a National Geographic study the teeth of urchins were shown to be able to chew through stone without becoming blunt.
The gonads of sea urchins, both male and female, can be found in culinary delicacies in various countries around the world. I have dived with Spanish divers who enjoy eating them raw. In Italy sea urchin (ricci) roe is used in pasta sauces.