This one of the bubble species which has identical polyp mantles to the fox coral, Nemenzophyllia turbida,
This species is seldom seen in LFS and frequently label as fox.
You can see the bubbles on the polyp when it is half open but is bearly visible when full expanded.
I have attached a pic, this was taken just now but it has not full expand. Will try to take a pic when fully expanded to show the resemblence.