The only mobile things are a gsm clown, a damsel, an orange linkia, snails, hermits and some anemones. There are some bristle worms as well.
I know that its not the fish or the linkia and I doubt that any of the snails did it.
I have a porcelain crab (I think) but he won't come out from under the anemone at the other side of the tank.
My guess is that its either this hermit or a hitchhiker crab. I was doubtful that it was the hermit as well but he was right in there and I haven't seen anything else near the xenia. Whatever it was basically pruned the xenia back to the stalks. I have him quarantined for now ... I was going to put in a xenia in with him to see if he went for it