Symbiotic association of crinoids, platyceratid gastropods, and Cornulites in the Upper Ordovician (Cincinnatian) of the Cincinnati, Ohio Region

The crinoid Glyptocrinus provided an elevated substrate on the Cincinnatian seafloor suitable for exploitation by platyceratid gastropods and their attached epizoans, notably Cornulites, a tubiculous, suspension-feeding worm-like organism. The presumably coprophagous platyceratids served as a substrate for settling larvae of Cornulites. Seven species of platyceratid gastropods belonging to the genera Cyclonema and Naticonema have been found with cornulitids attached commensally in several stereotypic locations on the shell. Some cornulitid individuals survived partial overgrowth by the snail shell and continued to live commensally on the snail. Whether coprophagous on the crinoid fecal wastes or not, the platyceratids and associated cornulitids represent opportunistic secondary tierers which occupied an optimally elevated position on the calices of Glyptocrinus, above an unstable, mud bottom substrate. Cornulites, and perhaps the platyceratids, very likely took advantage of food particles made available by the cri-noid's filter-feeding activities. This cornulitid-snail-crinoid association is documented in several stratigraphic units within the Cincinnatian Series.