THE ORGANIZATION OF MASTIGAMOEBA-SCHIZOPHRENIA N-SP - MORE EVIDENCE OF ULTRASTRUCTURAL IDIOSYNCRASY AND SIMPLICITY IN PELOBIONT PROTISTS

A new species of pelobiont, Mastigamoeba schizophrenia n. sp., is desc ribed using light and electron microscopy. Three forms were observed: flagellates, aflagellated amoebae and cysts. This species is distingui shed by having adhering paired nuclei. Most cells have a single pair o f nuclei but large amoebae may have several pairs. The flagellar appar atus consists of a single basal body, connected to the most anterior n ucleus by a cone of microtubules. The basal body is composed of double ts of microtubules. A single ribbon-like microtubular root originates alongside the basal body. Like other pelobionts, the cell has a compar atively simple endomembrane system which includes endoplasmic reticulu m but lacks mitochondria, dictyosomes, contractile vacuole and other e lements found in many eukaryotic cells. The taxonomy of the pelobionts is discussed, the genus Phreatamoeba is synonymised with Mastigamoeba , and arguments for a deep-branching position for the pelobionts among eukaryotes are discussed.