Question about Cystoid (Echinodermata) layers

[mbarco]

I just realized that "some" Cystoidea (divided in the two classes: Rhombifera & Diploporita) have a layered theca. And so I entered into the world of Epitheca, Stereotheca, Treatise on invertebrate paelontology, outer layer,...

When I find something like this (see attached file), does that mean it was made up of multiple layers and the outside was removed?

If it's so, which Cystoids were layered? Everyone except Polycosmitida?

So, a similar specimen, gives no indication as to which Cystoid it belongs to?

Thanks a lot