The tenticles are not on the oral disk but around it just like any other button polyp. In fact I believe I have three exactly like the one you have there, can't get a pic right now as the wife would not like the flash going off in the bedroom right now. The also have been there quite a while, and my peppermint shrimp have eaten all the aptasia in the tank but leave these guys alone, except to step on them once in a while.
Test it, just touch it, if it goes into the rock then I'll say its aptasia, if it just closes its head and those litte tenticals close with it, but leaving a stem, then its a button polyp.
Thomas