| Summary: | Despite continuous efforts since the 1950s and more recent advances in culturing flagellates and nonflagellate cells of the prymnesiophyte Phaeocystis, a number of different life-cycle models exist today that appear to apply for P. globosa Scherff. and P. antarctica G. Karst., both spherical colony formers. In one such model, this life cycle consists of three different flagellates and one nonmotile cell stage that is embedded in carbohydrate matrix-forming colonies of different sizes and forms. Recently, noncolonial aggregates of diploid nonmotile cells attached to surfaces of diatoms were put forward as a new stage in the sexual life cycle of P. antarctica. However, it can be discussed that these attached aggregates (AAs) are an intermediate between motile diploid flagellates, with their well-known tendency to adhere to surfaces, and the young spherical colony with its diploid nonmotile cells, which in nature is commonly found attached to diatoms. A life-cycle model pertaining to both P. globosa and P. antarctica is presented.
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