Ok, crappy pics so Ill try to explain it the best I can. It looks almost like the tentacles of a squid poking out of one of my rocks. The tanks only a month or two old and the rock was completely dried when I put it in. I've added a couple frags to the tank along with other general livestock, so I don't know if it hitched a ride, but it looks bigger than any of my frags currently are, so it would have had to grow extremely fast.