The first record of endobiotic cornulitids in a heliolitid coral from the Hirnantian (Late Ordovician) of Estonia

A single specimen of Stelliporella sp. (a heliotid coral) from the Hirnantian of Estonia contains at least four specimens of endobiotic cornulitid tubeworm Conchicolites sp. The cornulitids settled on the living heliolitid colony and were subsequently overgrown by the host coral. The endobiotic cornulitids may have derived significant advantages from inhabiting stable substrates, such as the massive skeletons of corals, which offered both physical support and a reduced risk of dislodgement. The coral skeleton surrounding the Conchicolites specimens does not exhibit changes in geometry other than a change in the shape of growth lines above the cornulitid, suggesting a neutral impact on the host and possibly a commensal relationship.