Ultrastructure of Trimastix convexa Hollande, an amitochondriate anaerobic flagellate with a previously undescribed organization

Trimastix convexa is a free-living flagellate with four flagella and found in anaerobic habitats. The light microscopical appearance resembles that of Percolomonas and Tetramitus and some retortamonads, but the flagellate is shown to have an ultrastructural identity that is distinct from that of other quadriflagellate protists such as the Heterolobosea, retortamonads, diplomonads, oxymonads and trichomonads. The cell has a ventral groove bordered on the left by a microtubular root associated with a striated fibre, and on the right by a microtubular root. There are no other major non-microtubular roots or microtubular roots except a poorly developed microtubular dorsal system. The groove contains a recurrent modified flagellum with a vane reminiscent of retortamonads. The cell contains a Golgi apparatus and has hydrogenosome-like organelles but no mitochondria. On the basis of this information, we are unable to assign this species to any of the genera in which it has been previously described, and consequently classify it as Protista incertae sedis.