One of the most interesting of these parasites is the Rapa rapa snail. This snail is extremely specialized in that it is a boring snail that eats only Sarcophytons and Lobophytons (leather corals) and Sinularias (finger leather corals). It is a very difficult pest to detect, in that it bores to the center of the leather coral's stalk while it is small and then continues to eat the entire inside of the animal. I have had them in my tank twice and in each instance I can only assume that they arrived already inside the leather coral that I purchased. The only way that I knew they were present is that the leather coral started showing signs of stress as indicated by the stalk turning yellow and the polyps not expanding. On close examination of the coral, I found what looked like a small incision on the stalk where the coral had healed over. When I pushed on this incision the stalk broke apart revealing the snail doing his damage inside the stalk. When he was removed the coral regained its health in a couple of weeks.
