You can kill them with Kalk, Joe's Juice or Aiptasia X, just like Aiptasia, BUT, it usually takes at least 3 treatments, before they know they're dead. Otherwise, they just come back
Or, as was mentioned, you can remove them mechanically. I've even done it with a butter knife, or spoon, inside the tank. If you get the blade under their foot, you can give it a flick and usually pop them right off. They don't attach nearly as strongly as Aiptasia and don't seem to be as likely to bury their foot in a hole in the rocks. They're really easy to remove, if you get them while they're moving.
I've also removed rock, and removed them with a razor or knife. Don't cut the foot though...slide the blade under the foot and pop them off.
These didn't come from any of the frags you got from me did they? I do have some in my tank, and remove them a few at a time, here and there. I am very careful not to send them home with anyone....lol....though I suppose I could have missed one.