What are these?

[Flreefer]

I think consensus would say yes. They're in the same family as jellyfish and anemones, believe it or not from the looks of them, and have the ability to sting. They spread easily, are photosynthetic, and will inhibit growth or choke out zoo colonies. This I know first hand. My ever growing population of Coralline algea seems to overtake it though, and I swear my Copperband is eating it. I am not suggesting a Copperband as a means of removal, I had wanted one for a long time, and played a hunch , thinking these things were some type of tube worm.
If I could do it again,I would have removed it from my first batch of live rock. In the beginning I was thrilled with my first Aptasia, until I knew what it was, so I saw these as just another part of the whole system. They can quickly overpopulate a tank
I would remove it

 

[circus clowns]

Thanks for the info, mine is on a small piece of rock connected to my colt coral , I'll just clip it. And that's funny about the aptasias I did the same thing.