As to the origial fossil - At first I thought that it is an echinoderm of some kind, probably a section through the crown. My guess was pterotocrinus, such as the one seen at:
http://www.uky.edu/KGS/fossils/crinoid.htm
That would fit with Mississippian age limestone, but the symmetry doesn't match. It could be a wierd cross-section.
I have a hard time seeing it being a holdfast because you usually don't see that kind of symmetry in a holdfast. I thought that one cirri usually comes off one segment in the holdfast, not many radiating off one, but I could be wrong.
Another thought was that it could be a bryozoan, such as Evactinopora, but they usually have 4-8 spines, so this specimen has too many. There can be divisions in Evactinopora, which are mutual walls that are shared by zooecia, but again the symmetry doesn't make any sense.
There is nothing like it in Shimer and Schrock
Index Fossils of North America, and they have about everything.
I am stumped.