Endobiotic cornulitids in Upper Ordovician tabulate corals and stromatoporoids from Anticosti Island, Quebec

Conoidal shells ofCornulites celatusn. sp. occur commonly within host coralla ofPropora confertaMilne-Edwards and Haime, 1851, sensu lato, from the Laframboise Member of the Ellis Bay Formation (Ashgill: Upper Ordovician) at Pointe Laframboise on western Anticosti Island. Examples have also been found at the same locality in the tabulate coralsPaleofavositessp.,Acidolites arctatusDixon, 1986, andA. compactusDixon, 1986, and the stromatoporoidEcclimadictyonsp., but not in other associated tabulate coral species. Growth interference between the shells and their hosts indicates a commensal relationship.C.celatusapparently had a more limited paleoenvironmental range than its principal coral host species, which occurs abundantly elsewhere on the island without its endobiotic partner. The diagnosis ofCornulitesis emended to include forms having a two-layered shell wall with a distinctive outer layer consistently preserved as prismatic calcite. This new species extends the known stratigraphic range of cornulitids in commensal relationships with corals and stromatoporoids from the Silurian back to the Upper Ordovician.