An SEM study of thecal division in Gonyaulax (Dinophyceae)

Abstract

The precise oblique plane of division of the theca is described for six species of Gonyaulax Diesing. This follows the pattern already defined for other genera such as Ceratium which share their thecal plates on division. New information is provided on the overlap of the plates and it is shown that along the fission line the plates on the right half overlap the left for all plates on the epitheca apart from the last precingular plate where the reverse is the case. In the cingulum and hypotheca the left half plates overlap those of the right. The cell division gives 11 plates to the right half-cell and 13 to the other (ignoring the sulcus). Image analysis studies suggest that in terms of thecal area the two halves have equal shares. The line of fission is discussed in relation to its taxonomic and evolutionary implications.