ultrastructural comparison between Spermatozopsis and Dunaliella (Chlorophyceae)

The ultrastructure of the type species of the genus Dunaliella, D. salina, has been reinvestigated in an attempt to clarify the relationships between Dunaliella and Spermatozopsis. Dunaliella salina differs in the following ultrastructural characters from Spermatozopsis (as exemplified by S. similis Preisig et Melkonian): presence of a distinctive surface coat covering the plasmalemma; presence of a prominent pyrenoid (with pairs of thylakoids partially entering the pyrenoid matrix); dictyosomes parabasal; endoplasmic reticulum closely underlying the plasmalemma around most of the cell; contractile vacuoles absent; cell form ovoid to elongated and not spirally twisted; mitochondrial profiles near the flagellar apparatus. Differences in the ultrastructure of the flagellar apparatus: basal body angle more or less fixed; distal connecting fibre cross-striated; system II fibre (rhizoplast) present, associated with mitochondrial profile; system I fibre underlying two-stranded microtubular root; mating structure present. These ultrastructural differences justify distinction between the two taxa at generic level. The problematical status of "freshwater" species of Dunaliella is briefly discussed.