Devonian of Illinois Identification Help

[Thomas.Dodson]

This beautiful specimen came from the Clear Creek Formation (Devonian) of Illinois in Union County. Does anybody have any ideas for identification?

[piranha]

Cyclocystoid

[FossilDAWG]

I agree there is a considerable resemblance to a cyclocystoid, but something seems off to me.  For one thing the "marginal ring" seems to be the same material as the matrix, rather than calcite plates.  Also the central disk does not seem to be made up of numerous small plates, and there is no evidence of radiating channels.  Admittedly those features are usually only clearly seem on especially well preserved specimens.  Anyway I think this is an impression (mold) with none of the original shell preserved, but I can't say what sort of an organism it was.

 

Don

[piranha]

A cross section of a Devonian receptaculitid is another look-alike possibility.  This Silurian specimen shown only for illustrative purpose. 

 

 

Nitecki, M.H. 1972. North American Silurian Receptaculitid Algae. Field Museum of Natural History, Fieldiana Geology, 28:1-108  PDF LINK

[Tidgy's Dad]

I know it's not going to be a popular guess for a lot of reasons, but I smell bryozoan.

 

[Thomas.Dodson]

Whatever it is it seems cyclocystoids from the Devonian of North America are rare. (according to Fluegeman, Richard H., and R. William Orr. “Occurrence of Sievertsia (Echinodermata: Cyclocystoidea) from the Middle Devonian of Northern Indiana.” Journal of Paleontology, vol. 64, no. 3, 1990, pp. 480–482.)

 

That doesn't eliminate it but is worth consideration. It might not be diagnostically relevant but I find it interesting that the central disk seems much more convex than available images of cyclocystoids.