Cyclocystoid - Zygocycloides sp.
This echinoderm is an extremely odd and poorly undersood.
Even their digestive system (i.e. anus and mouth arrangement) isn't completely known.
Most of the time, individual plates from the rim are found scattered among the shells and
matrix material. On occasion, complete individuals are found. The picture is that of my own
cyclocystoid. I've made a link to one that has some of the smaller details still preserved.
About the specimen
This is from Ordovician of Ohio from the Oregonia Member of Arnheim formation.
(Left) Here's my cyclocystoid. It's just under a centimeter long. Isn't it cute? (right)
Reconstruction of the cyclocystoid Zygocycloides magnus. Sketch by Dr. Colin Sumrall, courtesy of
DryDredgers.org, from their
Wierd Echinoderms of the Cincinnatian page.
Here's a beautiful example of another cyclocystoid
Link from the Kentucky Paleontological Society