Creneis carolina gen. et sp. nov. (Heterolobosea), a novel marine anaerobic protist with strikingly derived morphology and life cycle.

We report the light-microscopic morphology and ultrastructure of a novel free-living, heterotrophic protist, Creneis carolina gen. et sp. nov. isolated from marine anoxic sediments. C. carolina is a heterotrophic, obligately anaerobic amoeboid flagellate, and superficially resembles Mastigamoeba (Amoebozoa: Archamoebae) or Breviata (Breviatea) by possessing a single anterior flagellum closely associated with the nucleus, and because it appears to be an anaerobe. However, its life cycle contains multiflagellate cells with an unusual morphology. The structure of the mastigont of C. carolina is unique and not readily comparable with any eukaryotic group. Unexpectedly, phylogenetic analyses of SSU rDNA and of a concatenate of α- and β-tubulin genes with SSU rDNA convincingly showed that C. carolina is a member of Heterolobosea and belongs to the taxon Tetramitia.