Malawimonas jakobiformis n. gen., n. sp (Malawimonadidae n. fam.): A Jakoba-like heterotrophic nanoflagellate with discoidal mitochondrial cristae

Malawimonas jakobiformis n. gen., n. sp., is established for a bacterivorou s heterotrophic nanoflagellate isolated from the Malawi shore of Lake Nyasa (eastern Africa). Trophic stages observed were anteriorly biflagellate and naked. The posterior flagellum of a trophic cell resided in a conspicuous groove on the ventral surface, and bore a prominent vane. A Golgi stack and a mitochondrion with discoidal cristae were present anterior to the nucleu s. The kinetid consisted of two short, slightly separated basal bodies, fou r microtubular roots, and associated fibers and bands. The three microtubul ar roots associated with the posterior basal body were associated with the ventral groove, while the single root associated with the anterior basal bo dy gave rise to secondary cytoskeletal microtubules. Dividing cells became rounded, with persistent flagella. Cysts were uninucleate, and had thin org anic walls without clearly differentiated apertures or ornamentation but wi th conspicuous attachment pads. Kinetid elements were present within cysts. On the basis of microscopical features, especially those of the kinetid, t he nearest relatives of M. jakobiformis are the mitochondriate "jakobid" pr otists (families Histionidae and Jakobidae) and the amitochondriate retorta monads. Malawimonadidae n. fam. is established to accommodate this species.