Really Wild Coral I.D.

That is what a Scolymia skeleton looks like. It seems much more likely to me that the Scoly died off during shipping or something and is just coming back. I don't have a book handy to disprove the fungia/plate coral theory but it seems like the simplest answer is dieoff and return rather than a coral growing on another coral's skeleton.

JMO though.

 

is it on its own skeleton or growing on a skeleton. look at the pic after it has been under a powerhead.

 

If I understand your point correctly that you're trying to distinguish between growing "on" the skeleton as opposed to just growing back "into" the old skeleton.
I believe it's common when a coral dies off/recedes, it doesn't necessarily reuse the exact same skeleton it had before but sometimes (maybe most of the time) will create new skeleton and re-encrust over the old skeleton or form a brand new skeleton all together, perhaps reusing part of it (probably most obviously the part that didn't die). I would expect it to look like it's growing "on" a skeleton, not just filling out the old skeleton with new tissue.

It might depend on the amount of recession that happened and whether the matrix underneath the surface of the skeleton died off. Additionally it could depend what type of growth form the coral has, in this case with what appears to be Scolymia they are generally solitary polyps so it might make sense if they recede they would need to start growing from scratch because there's not a lot of underlying living tissue towards the edges of the coral.

Some of this is just speculation on my part but I believe the basics of it are pretty sound. I would be happy if someone could provide more information about it. I'm just beginning to learn about all the intricacies of coral biology.

 

I have to agree with Screwtape, it doesn't make a lot of sense for it to be growing on another coral's skeleton. It probably receded at some point and is making a come back. It also makes sense that as it grows, it will create a new skeleton, not reuse the old one.