Thanks for reply. It has no skeleton. just started growing out of the rock. I have just found another one that has just recently started growing off another rock too.
Doesn't really look like any of the majanos I've seen (I've seen a lot - my tank is overrun with the ugly brown ones) and it's certainly not an Aiptasia.
On the plus side, it's moderately good looking.
On the minus side, if it does turn out to be a pest, you may have insane amounts of them before you realize that fact.