MORPHOLOGY AND LIFE-CYCLE EVENTS PYROPHACUS-STEINII (SCHILLER) WALL ET DALE (DINOPHYCEAE)

Cells of Pyrophacus steinii (Schiller) Wall et Dale are round and lens shaped and have and anteroposteriorly compressed theca. The epitheca has a truncated, conical horn and a hexagonally shaped apical pore pla te with two arched slits positioned off center. The cingulum is equato rial, narrow, and deep. The hypotheca is flat. The sulcus is narrow, s lightly curved, and recessed and does not reach the cell's antapex. Th e plate formula in these specimens of P. steinii is Po, 8', Oa, 13 '', 13C, 12''', 3p, 3'''' and 8S with a difference in the number of preci ngular (13 '') and postcingular (12''') plates. No additional posterio r intercalary plates were present (Oap). Pregametic stages of P. stein ii were observed during cell division via binary fission, with formati on of two cells and multiple division with formation of four and eight cells. These newly formed cells were pale in color and were enclosed in double-layered hyaline membrane. Gametes with gymnodinoid morpholog y were observed within the parental cells. Planozygotes are large and round and enclosed in double-layered hyaline membrane. Mature cell for ms are brown with a microgranular cytoplasm, storage bodies, and a red accumulation body. The hypnozygote exhibits triple-layered hyaline me mbrane, irregularly shaped and comparable with bulbous processes of Tu berculodinium vancampoae Rossigol resting cysts. Division within a hyp nocyst of P. steinii involves shedding the parental theca and the deve lopment and emergence of two daughter cells with the size and morpholo gy of pregametic cells.