Evolutionary History of Colonial Organisms as Hosts and Parasites

Parasitic associations involving colonial animals are farily evenly distributed through the post-Cambrian Phanerozoic and have a long evolutionary history. Parasitism may have played an important role in the evolution of colonial animals. In the Paleozoic, the majority of marine symbioses involved colonial animals, and it is likely that colonial animals were also important hosts of parasites in the Mesozoic and Cenozoic, but further studies are needed. In the Paleozoic, stromatoporoids and corals were the most common hosts to various invertebrate parasites. Corals continued to be important hosts to parasites in the Mesozoic and Cenozoic. In addition, colonial animals themselves often infest or otherwise live in association with other organisms and can be parasites; however, colonial animals are more often hosts than parasites, and this has been so throughout the Phanerozoic. The stratigraphic distribution of parasitic associations in colonial animals is divided into two separate blocks: Paleozoic (Ordovician to Permian) parasitic associations of colonial animals form the frst block and Mesozoic to Recent parasitic associations of colonial animals form the second block. This division of parasitic associations corresponds well to the Sepkoski Paleozoic and Modern faunas and therefore these subdivisions are termed as the Paleozoic and the Modern parasitic associations of colonial animals.