On the identity of the freshwater dinoflagellate Glenodinium edax, with a discussion on the genera Tyrannodinium and Katodinium, and the description of Opisthoaulax gen. nov.

Abstract

Within the context of the preparation of a flora for the identification of freshwater dinoflagellates, the identity of Glenodinium edax and the affinities of a group of phagotrophic species with a conspicuous eyespot not associated with plastids (eyespot type C) currently classified in Katodinium were re-evaluated. The original description and illustrations of the phagotrophic G. edax suggest affinity with the Pfiesteriaceae. Whereas the tabulation currently associated with G. edax is based on a probable misidentification, the similarity to Tyrannodinium berolinense suggests that the two names can be regarded as synonyms and T. edax comb. nov. is proposed. As presented in modern floras, Katodinium is artificially defined on the basis of the position of the cingulum at or below the posterior third of the cell, and includes widely different forms. The presence of an eyespot of type C in the phagotrophic Katodinium vorticella and related species combines with a general cell morphology reminiscent of Esoptrodinium gemma and the formation of Tovellia-like cysts to mark this group of species as belonging to the Tovelliaceae. The type species of Katodinium, K. nieuportense, is morphologically quite different from these species and does not display tovelliacean characters. None of the known genera of Tovelliaceae matches the characters of K. vorticella and its close relatives. Opisthoaulax gen. nov. is described and new combinations are proposed for K. vorticella and six other species.