Morphology, Ontogenesis and Molecular Phylogeny of Neokeronopsis (Afrokeronopsis) aurea nov. subgen., nov. spec. (Ciliophora: Hypotricha), a New African Flagship Ciliate Confirms the CEUU Hypothesis.

Neokeronopsis (Afrokeronopsis) aurea nov. subgen., nov. spec. was discovered in soil from the floodplain of a small river in the Krueger National Park, Republic of South Africa. Its morphology, ontogenesis, and 18S rDNA were studied with standard methods. Furthermore, we supplemented the data on N. (N.) spectabilis by reinvestigating the preparations deposited in the British Museum of Natural History. Neokeronopsis (Afrokeronopsis) aurea is a very conspicuous ciliate because it has an average size of 330 × 120 μm and is golden yellow due to the orange-coloured cytoplasm and citrine cortical granules. Further main characteristics include the semirigid body; the urostylid cirral pattern with a distinct corona of frontal and pseudobuccal cirri both originating from the midventral rows; multiple anterior fragmentation of dorsal kineties 1-3; multiple posterior fragmentation of kinety 3, commencing with an unique whirl of kinetofragments; three caudal cirri; an oxytrichid/cyrtohymenid oral apparatus with polystichad paroral membrane and buccal depression; a single oral primordium developing along the transverse cirral row; and an oxytrichid 18S rDNA. These peculiarities are used to establish the new oxytrichid family Neokeronopsidae, the new subgenus Afrokeronopsis, and the new species N. (A.) aurea. Further, these features confirm the CEUU hypothesis, i.e., convergent evolution of a midventral cirral pattern in urostylid and oxytrichid hypotrichs; additionally, N. (A.) aurea is the first (semi)rigid hypotrich with cortical granules and the second one with midventral rows, breaking the granule and flexibility dogmas. These and other observations show that the phylogeny of the hypotrichs is full of convergences. Thus, only a combined effort of classical and molecular phylogeneticists will provide the data needed for a natural classification. Based on the CEUU hypothesis, the molecular data, and literature evidence, we suggest that midventral oxytrichids should be ranked as distinct families; accordingly, we establish a further new family, the Uroleptidae, which forms a distinct clade within the oxytrichid molecular trees. Neokeronopsis is possibly related to Pattersoniella because it has the same special mode of forming the buccal cirri and possesses a buccal depression found also in Steinia, a close relative of Pattersoniella. The large size and conspicuous colour make N. (A.) aurea a biogeographic flagship possibly confined to Africa or Gondwana, while Neokeronopsis (N.) spectabilis (Kahl, 1932) is an Eurasian flagship.