Ok, if I'm understanding this, this is what I can see, from the stalk it goes to a skin like area which they all seem to be a part of, and then it's on the rock. Not sure if that helps or if that is a hard skeleton.
They are so unlike zoos, they almost shrink down when a crab touches them the stalk collapes and they turn into small flowers, they don't fold in like zoanthids, that's what made me start to wonder. I know there are many different types of zoanthids, I was just curious, heck the guy that sold them to me at the LFS
didn't even know what they were when I told him that's what I wanted and he owns the store! Scary huh.