its a spiny urchin i believe??? its my boyfriends' urchin - had to have it yunno! he has it in a 75 gal and i honestly think it's too small for it. it eats all the algae out of the tank and the left over food n stuff. i'm a little concerned it's starting to eat his coralline too so we're trying to consider the possibility of moving him to his next location, wherever that may be...