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Four free-living, heterotrophic flagellates from dystrophic bog lakes in Northern Germany were examined by light and electron microscopy: Cyathobodosp., Rhipidodendron huxleyi, Spongomonas sacculus, and Spongomonassp.

The surface structures of different oxymonads (fam. Oxymonadidae) were light and electron microscopically investigated with respect to their morphology, chemical nature and distribution in the different oxymonad genera. Two species, Microrhopalodina multinucleataand Oxymonassp. were focused on and, since ultrastructural reports of oxymonads are scarce, some attention was also paid to their morphology. The cell surface of both species is totally covered with extracellular surface structures (ESS) to which bacteria are attached. The ESS are not detectable in the light microscope, but in the scanning electron microscope a continuous cover composed of circular structures is visible. They are found in indentations of the plasma membrane and consist of a cylindrical, hollow basis on top of which lies a circular lid. Digestion experiments and labeling with lectins and Ruthenium red allowed the conclusion that they mainly consist of carbohydrates and not protein. The presence of ESS seems to be a principal feature of termite flagellates belonging to the genera Microrhopalodinaand Oxymonas. The morphology of M. multinucleataand Oxymonassp. resembles that of other oxymonad species. Their karyomastigonts include an axostyle, a preaxostyle, and two pairs of basal bodies per nucleus. Additionally to the axostyles, a further microtubular rod extends into the rostellum. The numerous large vacuoles with fluffy contents are final stages of digestion vacuoles rather than sites for production of the ESS.

The behaviour of contractile vacuole complexes of representatives of the Cryptophycean genera Chilomonas, Cryptomonas, Cyathomonas and Rhodomonas is described using light and electron microscopy. The contractile vacuole occupies a fixed position in the cell, lying adjacent to the flagellar pocket/groove. A small region of the flagellar pocket is invaginated so that the plasma membrane lies close to the membrane of the contractile vacuole. This region acts as the pore through which the contents of the contractile vacuole are discharged. Discharge follows the fusion of the contractile vacuole membrane with the plasma membrane of the pore. Filling initially involves the fusion of small vacuoles which appear around the contractile vacuole shortly before the discharge of its contents. After these vacuoles have fused, filling may continue by the accretion of small vesicles which form the spongiome surrounding the contractile vacuole. Two types of vesicles have been identified in the spongiome. One type is involved in the filling of the contractile vacuole, the other in the retrieval of membrane from the filling vacuole. The first type appears to be produced by fragmentation of the contractile vacuole membrane during the discharge of the vacuolar contents.