Hybocrinus nitidus

From the Ordovician aged Bromide formation of Oklahoma come these Hybocrinus nitidus. These hail from an odd group of primitive Echinoderms that may be precursors to Blastoids. I can't find too much basic information on them on the internet and anything more specialized are in professional journals.

You can clearly see the five fold symmetry when looking at the top of the calyx. The wider, triangular area near the top might be where the anus was located(?).





Another specimen



The narrow openings on the top of the calyx are where I presume the brachioles (feathery feeding fingers) would have been as there is no clear anatomy to suggest arms as in traditional Crinoids. If anyone knows more about these interesting creatures, please fill me in.