Observations of two distinct size classes in natural populations of Dinophysis with similar appearance to normal vegetative cells were first reported in Dinophysis schuettii (Jorgensen, 1923) and Dinophysis swezyae (Taylor, 1976); but Wood (1954), and Norris and Berner (1970) reported intermediate forms exhibiting a continuum between the two extreme sizes. Focused attention on Dinophysis spp associated with DSP outbreaks in the last decade has provided new examples of small cells in the genus, sometimes with contours dissimilar from the corresponding vegetative cells; dimorphic individuals; dimorphic populations, and large-small cell couplets. Nevertheless, most studies were hindered by the unavailabilty of cultures or by the usual moderate numbers of field populations of Dinophysis spp. Based on in situ observations of concentrated material during intensive samplings for cell cycle studies of D. acuminata, D. acuta, and D. caudata, and on laboratory incubations of single cell isolations of D. acuminata it is documented that: i) During in situ phased cell division, most cells divide normally, but some (1-10%, but occassionally up to 50%) undergo a "depauperating" cellular fission leading to dimorphic cell pairs (one half corresponding to a "normal" cell and the other to a small cell); ii) After separation and sulcal list regeneration, these dimorphic cells become D. skagii, D. dens and D. diegensis-like individuals, that can also be observed forming dimorphic couplets (large-small cells) attached by their ventral margins; iii) small cells can grow again to normal size, thus explaining observations of thecal intercalary bands, and intermediate forms. Although the sexual nature of the small cells has not been unequivocally demostrated, these observations suggest common patterns in life cycle strategies of Dinophysis spp. Intraspecific morphological variability of Dinophysis spp in a given geographic area can be largely justified by small cell formation, part of the putative sexual cycle of these species. This once again draws attention to the need for a major revision of the genus.