The ultrastructure of Pedinomonas tenuisMasiuk, 1970 a hyperhalolimnetic green alga has been described for the first time with particular reference to the flagellar apparatus. Two kinetosomes show counter-clockwise orientation and end-to-end position. Microtubular rootlet system corresponds to the formula 3-2-3-1. Each of the two posterior rootlets is associated with a fibrillar rootlet and lies in nuclear furrows. Chloroplast has internal compound pyrenoid without starch cap (not visible under light microscope) and a stigma at the dorsal side. The hollow spheric mitochondrion with an orifice at one pole is displaced to the left side of the cell. The ultrastructure of this species has been compared with that of other Pedinomonas species and Resultor mikron which is very similar to P. tenuis. The differences between two latter species correspond to the species level. The common ultrastructural features of Pedinomonas include the important characters of Resultor. It has been proposed to recover the old name Pedinomonas mikron Throndsen for Resultor mikron Moestrup.