Calcified Symbiotic Settlements of Cyanobacterial Communities on the Reticulate Surface of the Skeleton of the Unusual Ordovician Eocrinoid Bolboporites (Echinodermata)

The study of the microstructure of the encrustations found exclusively on the lateral coarsely cellular surface of the unusual echinoderm Bolboporites, interpreted by us as an eocrinoid with the stem and theca fused into a single skeletal structure, showed their cyanobacterial nature. Calcification of cyanobacterial films indicates a high saturation with calcium carbonate and a low concentration of CO₂ in a thin layer of water on the reticulate surface of the Bolboporites, which is the opposite of the typical water conditions in the Baltic paleobasin. The features of the morphology and location of encrustations on Bolboporites suggest that the encrustation was cyanobacterial communities settled and developed during the life of the animal, and that they may have persisted for a short time after the death of the Bolboporites.