Title says it all- I think its a longspine urchin, black in color about 8 inch diameter and neon blue lines outlining the body. ate him alive-cracked the shell and ate a few legs and damaged his body.
I kid you not deano, the urchin caught the crab attacked and dragged it halfway up the glass, at that point i noticed and separated them but it was too late for the crab.
my rainbow urchin picks up hermit crabs and carries them around all the time. the minute they get close he latches on to them, but he hasn't killed one yet, and he puts them down eventually.