Gift rock

[Bradley Crocker]

Yep...cup coral. A type of Dendrophyllia. I have a few on one of my rocks as well. They're pretty rare in the hobby, and near impossible to frag.
I also think they're non-photosynthetic, so don't cook the little guy.

 

[Lionfish Lair]

One hint that it's something like a hidden cup coral and not an aiptasia, mojano or pest anemone is there are dead cup coral-type skeletons on the rock around it.

 

[Bradley Crocker]

I wouldn't be surprised if there's more than two heads. The one to the right of the largest looks like it could still be in there.

 

[flyman100]

That is not aptasia what you need to do if it is geat a dancing shrimp that will get rid of it.

 

[LbulletM]

+1 on hidden cup coral. I have a few on my Florida rock. Really pretty spots on the feeders.