New endobiotic cornulitid and Cornulites sp. aff. Cornulites celatus (Cornulitida, Tentaculita) from the Katian of Vormsi Island, Estonia

Two species of endobiotic cornulitids are described from heliolitid corals of the Katian (Late Ordovician) of Estonia. They are thus far the earliest known showing this symbiotic relationship. Conchicolites hosholmenis n. sp. represents the only known symbiotic coral endobiont species in the genus. Cornulites sp. aff. Cornulites celatus closely resembles the North American endobiotic species C. celatus from tabulates of the Hirnantian (Late Ordovician).