Auxospore Formation in Two Marine Clones of the Diatom Genus Coscinodiscus

Auxospore formation has been observed in two marine clones of the diatom genus Coscinodiscus. In each of these clones the variation in valve morphology and structure before and after auxospore formation is appreciable. This variability suggests a reappraisal of the taxonomic characters within the genus will be required if the kinds and types of variation noted are substantiated in other clones. The clones are monecious and the 32 uniflagellate colorless monads, inferred from indirect evidence to be male gametes, form within an undifferentiated mother cell. The method of release of the male gametes differs in the two clones; otherwise their development is similar. The zygote is recognizable and the formation of large diameter cells within the zygote membranes has been observed.