Lee, J. J., M. E. McEnery, E. G. Kahn, and F. L. Schuster. “Symbiosis and the evolution of larger foraminifera.” Micropaleontology (1979): 118-140.
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A new species of symbiotic algae, Chlamydomonas provasolii, has been isolated from the soritid foraminifers Cyclorbiculina compressa (d’Orbigny) and Sorites marginalis (Lamarck), and compared with the symbiotic alga Chlamydomonas hedleyi Lee, Crockett, Hagen and Stone from Archaias angulatus (Fichtel and Moll). The new species is distinguished by the structure of its pyrenoid and chloroplast. The dinoflagellate Symbiodinium microadriaticum Freudenthal, which is the dominant algal symbiont in S. marginalis, has also been identified with fresh isolates from the “upside-down jellyfish,” Cassiopeia frondosa. The presence of 3 different species of symbiotic algae in modern soritids suggests a general adaptation for symbiosis in larger foraminifera. Nutritional experiments indicate that the symbionts have the same requirements in the different hosts, and that the hosts must feed in order to satisfy the vitamin requirements of the symbionts. It is possible to interpret the cytological differentiation of S. marginalis, which is multinucleate and heterokaryotic with separate regions devoted to feeding and photosynthesis, as an acellular or coenocytic lower protist colonialism. The physological, cytological and physiological evidence from modern large foraminifera, taken with morphological and paleoecological data from fossil examples, strongly suggests that the iterative evolution of “giants” in different lineages was fueled by symbiosis.