The organisation 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 described using light and electron microscopy. Three forms were observed: flagellates, aflagellated amoebae and cysts. This species is distinguished by having adhering paired nuclei. Most cells have a single pair of nuclei but large amoebae may have several pairs. The flagellar apparatus consists of a single basal body, connected to the most anterior nucleus by a cone of microtubules. The basal body is composed of doublets of microtubules. A single ribbon-like microtubular root originates alongside the basal body. Like other pelobionts, the cell has a comparatively simple endomembrane system which includes endoplasmic reticulum but lacks mitochondria, dictyosomes, contractile vacuole and other elements 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.