Ultrastructural identities of Mastigamoeba punctachora, Mastigamoeba simplex and Mastigella commutans and assessment of hypotheses of relatedness of the pelobionts (Protista)

The ultrastructural appearances of Mastigamoeba punctachora, Mastigamoeba s implex and Mastigella commutans are described. All three species have elect ron-dense membrane-bounded bodies, suggestive of mitochondrial homologues. All species have a single basal body giving rise to conical arrays of micro tubules and to a single ribbon-like microtubular root. The proximal portion of the root is associated with a sheet of dense material. All species have '9+2' flagellar axonemes, with basal bodies composed of triplets of microt ubules, but axonemal outer dynein arms appear to be absent. All have a cyli nder at the base of the transition zone. The transition zone of Mastigamoeb a punctachora is elongate and also contains a column of electron-dense mate rial. Ultrastructural data are compiled and analysed to assess two alternat ive views - that the pelobionts are a primitive group of eukaryotes and the source of the other eukaryotes, or that they are related to eumycetozoan s lime moulds.