Mastigamoeba (massed-ig-a-me-ba) One of about 5 genera of pelobionts. These organisms are unusual in lacking mitochondria, dictyosomes and were for some time regarded as the most primitive of all eukaryotes. Most species which have been studied can adopt a variety of morphologies - including flagellates, amoebae, and cysts. The flagellates typically have one very long flagellum which beats in a fairly ineffectual fashion - and mostly progress by gliding. Body of cell most usually adopts an amoeboid form - such as that illustrated here. Typically found in habitats with little or no oxygen. This is Mastigamoeba invertens, a species which does not seem, from a molecular perspective, to be closely related to other species placed in the same genus. Phase contrast.