Dinoflagellates: Investigation and phylogenetic speculation

The changing views on the systematic position of dinoflagellates (Phylum Pyrrophyta, Class Dinophyceae) from their first discovery up to the present are recounted. Always a problem group, they owe affinities to the Protozoa and the algae and their supposedly primitive nucleus provides a link with procaryotes. The structure and division of the mesocaryotic nucleus is discussed; the unique flagella are described and the variety of nutritional and chloroplast types provide speculative evidence for the evolution of the group. A consideration of the cell covering (theca; amphiesma) provides information about the relationship within the group and this leads to a consideration of the phylogenetic position of the order Prorocentrales. It is concluded that the dinoflagellates are basically an ancient group which has only recently developed autotrophy. Their unique mixture of primitive and recently evolved characteristics seems to enable them to be an extremely successful group of protists.