Symbiosis in corals and stromatoporoids from the Silurian of Baltica

The large collection of thin sections of stromatoporoids and corals from the Silurian of Ukraine, Moldova, Belarus, and Komi Republic (Russian Federation) revealed several incidences of skeletal intergrowth between stromatoporoids/corals and the other invertebrates. The stromatoporoids formed symbiotic associations with soft-bodied worms (Helicosalpinx and Chaetosalpinx), calcareous tentaculitoid tubeworms (microconchids, Cornulites, Conchicolites), and rugosans. Tabulate corals formed symbiotic associations with cornulitids. The studied stromatoporoid based associations are dominated by bioclaustrations of worms without mineral skeletons. Most likely non-mineralized invertebrates benefitted more from endobiotic life mode than invertebrates with mineralized skeletons as the latter already had protection on their own against predators. There was almost no difference in the number of symbiont taxa per host stromatoporoid species indicating that all studied stromatoporoids were rather similar in their tolerance towards different endobionts.