It looks like an aptasia, but I've never seen that color in them. Get a pepermint shrimp. They eat those nasties. I had a few and went out and got a pepp. No more aptasia. Sometimes the pepps will only eat it down to a certain level, so it will re-grow. That way they always have some to eat. They don't bother anything else. Heck I hardly ever see mine now that he ate the aptasias.