Thecal apex structure in the Peridiniaceae (Dinophyceae)

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Abstract
Scanning electron microscopy has been used to observe the details of the apical structure of the theca in 46 species belonging to 10 genera (Boreadinium, Diplopsalis, Diplopsalopsis, Dissodium, Lebouraia, Oblea, Peridiniopsis, Peridinium, Protoperidinium, Zygabikodinium) in the family Peridiniaceae (Dinophyceae). The apex consists of an apical pore, pore rim, pore plate, canal plate and apical collar sections. Two new terms ‘section of ventral apical collar’ and ‘brim’ are proposed for structures found in some freshwater and marine species. In the organisms examined there are clear differences in the number of apical collar sections and the species have been categorised using this as a main character. The general use of the apical characteristics in the taxonomy of the family Peridiniaceae is discussed and the various types of apex are illustrated with scanning electron micrographs.