lol ....holy cow. I just realized what it is. I ordered a rainbow Monti but the all I got was the frag plug with the frag missing. Guess it dropped it the sump 2-3 weeks ago. Looks like the polyps is hanging on. I'll remount and see if it can be saved.
I may be wrong but it looks more like something long the lines of porites or some other encrusting coral. All the tunicates I have seen are more fleshy