Aviisotricha hoazini n. gen., n. sp., the Morphology and Molecular Phylogeny of an Anaerobic Ciliate from the Crop of the Hoatzin (Opisthocomus hoazin), the Cow Among the Birds.

The hoatzin is the only known avian species that has evolved a foregut fermentation system similar to that of ruminant animals. Due to the closeness of the bird's fermentation chamber, the crop, to the bird's beak it exudes an unpleasant odour; therefore, the hoatzin is called the "cow among the birds". In addition to Eubacteria and Archaea, responsible for digestion of the vegetation they consume, the bird's crop contains a holotrich ciliate, described here for the first time in detail. Cytological staining of this isotrichid-like ciliate with the Chatton-Lwoff and Protargol staining procedures, as well as SEM and TEM, justified the establishment of the new genus Aviisotricha n. gen. with its new type species Aviisotricha hoazini n. gen., n. sp.. Phylogenetic analyses of a portion of the small subunit rRNA gene supported the taxonomic placement of this new genus and species in the family Isotrichidae. Aviisotricha is compared with Balantidium, Dasytricha and Isotricha with special reference to their dorsal brushes, which show similarity to the paralabial organelle of the Entodiniomorphida. The possible phylogenetic origin of Aviisotricha is discussed and a taxonomic revision of the family Isotrichidae is given.