PLANOZYGOTE DIVISION AND OTHER OBSERVATIONS ON THE SEXUAL CYCLE OF SEVERAL SPECIES OF DINOPHYSIS (DINOPHYCEAE, DINOPHYSIALES)(1).

A life-cycle model has been proposed for Dinophysis, but several transitions between stages of this cycle needed more detailed description. In this study, the steps from mating gamete pairs, cell fusion, nuclear fusion, and the fate of planozygotes were tracked and described from incubations of different sexual-cycle stages of D. acuminata Clap. et J. Lachm., D. cf. ovum F. Schütt, and D. acuta Ehrenb. There were several pathways for depauperating division and formation of small and intermediate cells; observed mating tubes that connect mating gamete pairs were more delicate than the feeding tube described in D. acuminata; nuclear fusion occurs following cell fusion. Planozygotes were able to divide and produce several vegetative cells 2-3 weeks after incubation. New pathways were added to the revised sexual life-cycle model of Dinophysis spp. It is hypothesized that planozygotes are the main diploid sexual stage that may be involved in overwintering and seeding strategies. The importance of planozygote division, without further maturation into a resting cyst, as an adaptive strategy for holoplanktonic organisms is discussed.