The taxonomy and systematics of freshwater armored dinoflagellates

Abstract

Twenty-two species in eleven genera of freshwater armored dinoflagellates found in Texas were investigated. The taxonomic evaluation of each species included a review of the original description and subsequent work, and my observations of living and preserved material. Previously unreported details of the external morphology were revealed during specimen examination with the scanning electron microscope. A key to the species in each genus was written. The results of the taxonomic analysis were used to construct a phylogenetic tree. The phylogenetic diagram was drawn emphasizing four main lines of evolution in the taxa studied. Dinoflagellates are a monophyletic group with a Gymnodinium-like ancestor. Woloszynskia is a pleisiomorphic genus; species based on cyst configuration alone are removed from the genus. Lophodinium is related to Woloszynskia but has derived characters such as flagellar pore modification and vertical ridges. The plate number and symmetry of Sphaerodinium place it between the genera with many plates and the genera with fewer plates in the evolutionary diagram. It is not synonomous with Glenodinium cinctum. Peridinium is divided into two genera, Peridinium s .l. (encompassing Peridinium s.s.), and an as yet un-named genus based on the Umbonatum group. They are differentiated by plate tabulation, cingular and sulcal plate arrangements, ornamentation, size, and plate thickness. Hemidinium and Bernardinium are a highly derived sister-group to Peridinium s .l. Two species of Peridiniopsis (P. qymnodinium, P. quadridens) are related to the Umbonatum group based on plate similarities. Kansodinium and Durinskia are new genus names for Diplopsalis ambiquum and Peridinium balticum respectively; they are derived from the Umbonatum group by plate loss or fusion. The plate pattern of Thompsodinium is interpreted as 4', 3a, 6", 4S, 6C, 5'", 2""; it is allied to the Umbonatum group, but sulcal specializations separate it from the main line. Freshwater Ceratium is composed of two subgroups. Its long fossil history and number of species insure its designation as an evolutionary main line.