An endosymbiotic relation between the solitary rugose corals ?Yuanophyllum and ? Dibunophyllum and a large soft-bodied worm-like organism is described from the Hezhou Formation (Serpukhovian), Lower Yangtze Platform, South China. The endosymbiont lived in a U-shaped tube, probably with a horizontally sideways bent base connecting the vertical shafts. A membranous epidermis and relicts of a probable cuticulo-muscular tube are preserved. The corals reacted with skeletal encasement of the infesting organism and irregular, in part dense growth of additional skeletal elements adjacent to it. This is the first description of such an endosymbiotic, parasitic or commensal relation of solitary rugose corals after the Frasnian-Famennian Boundary Event. Similarities between the Devonian association of pleurodictyoform tabulates and the ichnotaxon Hicetes are remarkable. Moreover, the association proves the extraordinarily rare persistence of bioclaustrations in corals after the Hangenberg Event at the Devonian-Carboniferous boundary during the Permo-Carboniferous period of arrested endosymbiont development.