From what I remember, the way to tell Zoanthus from Paly's is that Paly's take sand into their coenenchyme, where Zoanthus don't. What are commonly called button polyps are Paly's (though, they can still be called Protopalys, as the reclassification didn't hit every type of button, only the PE form described above in surf's pics), and if you look at the coenenchyme, you'll see flecks of sand. I still think of Paly's as what they used to be to me, a mat like coral with mouths that open up and have virtually no coenenchyme (stalk). Big polyp size doesn't make it Paly...