The earliest endosymbiotic tubeworms have been discovered within skeletons of the tabulate coral Heliolites sp. from the Silurian (Ludlow) of Podolia, Ukraine. The new tubeworm species has a maximum diameter about 1 mm, a slightly conical tube, a smooth lumen in the tube and a lamellar wall structure. The tube wall is 0.05-0.10 mm thick. The new endosymbiotic tubeworm Coralloconchus bragensis n. gen. and sp. shares zoological affinities with the tentaculitids (incertae sedis) and is assigned to the Family Cornulitidae (Tentaculita, Cornulitida).