Light and electron microscopical studies onHafniomonas gen. nov. (Chlorophyceae,Volvocales), a genus resemblingPyramimonas (Prasinophyceae)

Based on light and electron microscopical studies ofPyramimonas reticulata the genusPyramimonas is shown to contain a number of unrelated flagellates.P. reticulata andP. montana are transferred to the new genusHafniomonas, cells of which differ fromPyramimonas in shape, in the absence of scales and hairs on the body and flagellar surfaces, in details of the chloroplast, the position of the nucleus, the Golgi apparatus, the internal structure of the flagellar apparatus, and in cell division. The prasinophytePyramimonas contains a characteristic association of a large microbody and a rhizoplast, situated on the nuclear surface. A similar association is being found in an increasing number of prasinophycean flagellates, but is absent inHafniomonas, which is considered related to chlorophycean rather than prasinophycean flagellates. The phylogenetic position ofHafniomonas is discussed, based in particular on details of the unique flagellar apparatus.