What can you guys tell me about these critters? I got one when I purchased some corals and rock from a fellow reefer. He siad it was harmless and had never had trouble in his tank from it. Are they harmless or can they cause problems of any kind? It looks like he is eating my coraline and now it is sitting on my shrooms. If it eats those I will kill it for sure. I know some urchins pack a pretty good sting and was wondering if he could have contributed to the unexplained death of my coral beuaty angel. Thanks!!