FURTHER SEM STUDY OF MARINE DINOFLAGELLATES - THE GENUS OSTREOPSIS (DINOPHYCEAE)

This paper presents a comprehensive examination of the taxonomy of the genus Ostreopsis Schmidt. The morphology of six species of marine din oflagellates, Ostreopsis siamensis Schmidt 1902, Ostreopsis lenticular is Fukuyo 1981, Ostreopsis ovata Fukuyo 1981, Ostreopsis heptagona Nor ris, Bomber, et Balech 1985, Ostreopsis mascarenensis Quod 1994, and O streopsis labens Faust et Morton 1995 from three geographical regions (Japan, Southwest Indian Ocean, and the Caribbean) and three marine ha bitats (sand, water column, and macroalgal surfaces) are described fro m scanning electron micrographs. Differences in the following morpholo gical characteristics differentiated the species: cell shape and size, and ornamentation of the epitheca, cingulum, and hypotheca. The theca l plate formula of the six Ostreopsis species is P-0, 3', 7'', 6C, 6S? , V-p, R(p), 5''', 1p, 2'''', with differences in thecal plate size an d shape. The cingulum in ventral view has two prominent structures: a ventral plate (V-p) with a ventral pore (V-0) and a ridged plate (R(p) ) that distinguishes Ostreopsis species from any other dinoflagellate taxa. This paper also includes ecological and toxicity information reg arding the six Ostreopsis species.