Ultrastructure and Taxonomic Observations on Marine Isolates of the Genus Nannochloris (Chlorophyceae)

The chlorophycean genus Nannochloris has historically been distinguished on the basis of two morphological properties: division into two and only two daughter cells, and absence of a surrounding mother cell wall during cell division. Our ultrastructural examination of five strains of Nannochloris frequently revealed multiple fission of cells and the presence of a mother cell wall. In several strains, the trilaminar structure of the cell wall was indicative of the presence of sporopollenin. On the basis of ultrastructural examination alone, these Nannochloris strains could not be distinguished from several known minute species ofChlorella, and the validity of Nannochloris as a distinct genus tnust be questioned. However, reclassification of the genus is not recommended until further work on the biochemical taxonomy of Nannochloris is undertaken.