Radiolarians are a major group of Rhizaria. Three orders of Radiolaria are characterized by a siliceous skeleton, and are called polycystines (Polycystina). The skeletons of polycystines are well preserved in sediments as fossils. These fossils are important for paleontological analysis; thus, many stratigraphic, paleoceanographic and taxonomic analyses of polycystine fossils have been conducted from the 19th century to the present day. However, there is a lack of data on living polycystine cells, and little is known about their biology and ecology because of the difficulties in collecting and culturing cells. Despite these difficulties, several reports have succeeded in examining living cells. These studies have clarified cell structure, pseudopodial activity, nutritional uptake, skeletal growth, and survival strategies. In this review, recent progress in experimentation on living polycystine is summarized, and unsolved problems are discussed. Polycystines inhabit an unusually long geological range from the Cambrian to the Present, and their evolutionary processes can be revealed by fossil analysis, which is an advantage in researching relationships among the paleoenvironment, paleoecology, and evolution. Further research into living polycystine cells would encourage new developments in both biological and paleontological researches.
Termites harbor a host species-specific symbiotic community composed of excavate protist species in their digestive tracts. Although termite-protist symbiosis is well known, our knowledge concerning the variations in symbiont species compositions and variations in community structures among individuals, colonies and host castes is very limited. Here we collected 11 colonies of the termite Coptotermes formosanus in the Western Japan Archipelago and investigated the variations in the protist species compositions. We investigated the symbiont community structures in three host colonies, and for the first time, variations of the community structures were compared between worker and soldier castes. Three parabasalian species, Pseudotrichonympha grassii, Holomastigotoides hartmanni and Spirotrichonympha leidyi, were observed in all examined host individuals in the 11 colonies. One small trichomonadid species was found in hosts obtained from Iriomote Island and Okinawa Island. The mean symbiont community size in the workers was 30–50 times larger than that of the soldiers, and the host caste had a significant effect on the protist community structure. A principal component analysis revealed that the community structure was significantly more variable in the soldiers compared to the workers. Differences in food quality and community size between these termite castes probably affect the protist community structure and its variations.