On dinoflagellate evolution.

A broad overview of the diversity of living dinoflagellates is presented in a hypothetical evolutionary context. Ultrastructural, and some physiological information is included. Five principal organizational types: prorocentroid, dinophysoid, gonyaulacoid, peridinioid and gymnodinoid, are taken to represent lineages, and the developments within each summarized. Thecal evolution is discussed party with the aid of a model developed to determine probable plate homologies in the gonyaulacoids and peridinioids. Both primitive and highly specialized features are drawn attention to, particularly with regard to the nucleus and ocelli. The parallelism between the latter and metazoan eyes is extraordinary, considering that the dinoflagellate organelles are made of subcellular components. The roles of various types of cysts within the lifecycle of dinoflagellates are discussed. The compatibility of the hypothetical events proposed here with the fossil record is briefly considered, and some indications of the phyletic position of dinoflagellates are reviewed. The conclusions summarize the principal developments that appear to have arisen within the group. The relative primitiveness of the desmokonts is affirmed. A new combination, Plectodinium miniatum (Kofoid and Swezy) comb. nov. is proposed, as well as the recognition of a new order, the Gonyaulacales ord. nov.