Ultrastructure and taxonomy of Paraphysomonas (Chrysophyceae) and related genera 3

New observations are presented on the internal ultrastructure of the scale–bearing chrysophycean genera Chromophysomonas, Chrysosphaerella , the new genus Polylepidomonas and 15 species of Paraphysomonas. These data show that the pigmented genera Chromophysomonas, Chrysosphaerella and Polylepidomonas have a generally similar internal structure and that their taxonomic separation is based only on differences in scale structure. The structure of Paraphysomonas resembles that of these genera but the cells always possess a leucoplast rather than a chloroplast. In cell structure, the pigmented genera resemble the naked genus Ochromonas while Paraphysomonas resembles Spumella , the colourless counterpart of Ochromonas. Evaluation of the differences between these genera and the scale–bearing genera Mallomonas and Synura has led to the conclusion that Chromophysomonas, Chrysosphaerella, Polylepidomonas and Paraphysomonas should no longer be classified within the family Mallomonadaceae. The new family Paraphysomonadaceae is established to include Chrysophyceae with an Ochromonas type of cell structure but which also produce silica scales.