TAXONOMY AND LIFECYCLE OF GENUS PHAEOCYSTIS (PRYMNESIOPHYCEAE)
QI Yu-zao, SHEN Ping-ping, WANG Yan (Institute of Hydrobiology, Jinan University, Guangzhou 510632, China)
Studies of the genus Phaeocystis, a most widespread marine Prymnesiophyceae, are reviewed. The taxonomy of this genus remains unclear so far. Taxonomic criteria of species are based on initial colony shapes, geographic distribution, free-living cell characteristics as well as chemical products, ploidy, genome size, 18rRNA and so on. Based on all of these taxonomic characters, Phaeocystis has been divided into four definite species at present: P. scrobiculata, P. antarctica, P. globosa and P. pouchetii. The first has only free-living cells and forming no colony, while the rest are of colony-forming species with not only single cell but also colonies composed of thousands of cells embedded in one mucilaginous matrix occasionally reached several mm in diameter. Phaeocystis has a complex heteromorphic life Cycle exhibiting alternation between two different morphological forms: free-living cells and colonies. The unicellular stage involves several types: non-motile, flagellates, microzoospores and possibly macrozoospores. However, their respective functionwithin Phaeocystis life cycle and, in particular, their involvement in colony formation are not completely understood.