Colonial Heterocorallia (Cnidaria, Anthozoa) and their epibionts from the lower Carboniferous of Montagne Noire and Pyrenees, southern France

Colonial heterocorals are uncommon faunal component of the Serpukhovian limestones of the Montagne Noire and Pyrenees in southern France. Four species are introduced into the newly established genus Semenomalophyllia. They all share the typical septal arrangement of heterocorals, at least in early stage of development. The fused axial ends of septa commonly withdraw during the ontogeny of larger sized species such as Semenomalophyllia herbigi and S. perretae. In S. weyeri, the septa are withdrawn from the axis and arranged in two series (‘minor’ and ‘major’) that show a striking morphological convergence with rugose corals. The corallites of the smallest species S. webbi are very similar to the solitary heterocorallian Heterophyllia ornata and possibly evolved from it. S. weyeri and S. perretae are commonly colonised by alcyonacean octocorals as indicated by the occurrence of sclerites covering the corallites. These are described as Lafustalcyon vachardi gen. et sp. nov., a new taxon yet only known in the Serpukhovian strata, and only affecting heterocoral colonies. In addition to the alcyonacean octocorals, a diverse assemblage of epibionts colonised the heterocorals: calcifying microbes, bryozoans, foraminifers, microconchids, crinoids, boring organisms, and microproblematica. Syn-vivo relationships can be demonstrated only between Semenomalophyllia and Lafustalcyon as the first commonly bio-immured the second. Other encrusting organisms could have colonised either living, erected colonies or broken or tilted dead colonies. © 2021, Paläontologische Gesellschaft.