Morphological details of the life history of Alexandrium minutum (Dinophyceae)

Different life stages and the processes of asexual division and sexual fusion of the toxic dinoflagellate Alexandrium minutum are reported. A sexual division is oblique, with the two identically sized daughter cells sharing the parent theca and synthesizing the remaining plates. As in many dinoflagellate species, gametes are indistinguishable from vegetative cells prior to mating. During gamete fusion, which is initiated by flagellar attachment, a wide range of relative gamete orientations were observed. The longitudinal flagella of resultant motile planozygotes are not necessarily situated adjacent to each other, and planozygotes have thus perhaps not been recognised in previous studies which used this characteristic for identification. There are similarities between the life histories of A. minutum and the closely related species A. tamarense. Dinoflagellates exhibit various modes of reproduction and the details of life histories which may cause confusion are highlighted.