Similarities in the Asexual Reproduction of the Oceanic Dinoflagellates,pyrocystis Fusiformis, Pyrocystis Lunula, Andpyrocystis Noctiluca1

SUMMARY Three cultured species ofPyrocystis(Dinoccoccales) reproduced asexually by forming 2 (or 1) aplanospores or zoospores inside the parent cell wall. In all 3 species these small reproductive cells, although they may not resemble the parent cells, swell up rapidly (∼ 10 min) to the approximate size and shape of the parent cell. These swollen cells become new vegetative cells. The above asexual process is the only way by which cells numbers increase in our cultures.Pyrocystis lunulawas propagated at the lunula stage of the life cycle. The nonmotile crescent‐shaped cells produced reproductive cells that wereGymnodinium‐shaped and had, in some cases, a trailing flagellum. WithP. fusiformisandP. noctiluca, the reproductive cells were not flagellated. WithP. fusiformis, these bodies had a pronounced equatorial constriction like a girdle, while inP. noctilucathe “girdle” was an inconspicuous feature if present. WithP. noctilucaandP. fusiformison a 12:12ldcycle, reproductive cells were formed early in the dark period and they swelled up at the beginning of the light period. Reproduction ofP. lunulawas not well phased in our experiments, with reproductive cells developing at the end of the light period and the end of the dark period.