Whatever it is its got to go. Its killed two chalice's and stung quite a few zoa's....its tentical can get up to around 8 inches long....never really noticed it before i started to see corals dieing behind it...Ive had this piece forever and kinda sad to see it go but glad i wont lose any more coral. Prolly not worth much. I already put it in the corner today here it is... back at it again.