Endobiotic tentaculitoids formed symbiotic associations with tabulates, heliolitids, rugosans, bryozoans, crinoids, stromatoporoids, and chaetetids from the Late Ordovician to the Carboniferous. The Ordovician was dominated by coral hosts, but there was a shift from mostly coral-based associations to stromatoporoid-based associations in the early Silurian. Specialization increased during the evolution of tentaculitoid symbiosis. In the Devonian, specialized symbiotic endobiont genera appeared which did not occur separately from their hosts.