Abstract
The oxytrichid ciliate Cyrtohymena citrina, isolated from a soil sample from India, is moderately flexible, measures about 105×35μm in life and possesses citrine cortical granules, mainly arranged around cirri and dorsal cilia. Morphology and ontogenesis was investigated using live observation and protargol impregnation, and 18S rDNA was sequenced. Ontogenesis of an Indian population of Urosomoida agilis was also investigated. All three genera included in the Urosomoida-Notohymena-Cyrtohymena group have long been characterized by the ontogenetic feature that “anlagen V and VI of proter originate de novo”. This ontogenetic feature has been considered as the sole synapomorphy and an important diagnostic feature of the group. Based on current observations on ontogenesis of C. citrina and U. agilis, and previous observations of C. shii, Notohymena saprai and N. australis, the aforesaid ontogenetic feature is no longer true for the group. Indian population of C. citrina clusters with C. muscorum, Paraurosomoida, Urosomoida, Notohymena and Paraurostyla, and is placed away from Oxytricha granulifera; all oxytrichids in the cluster show deviation(s) from any of the typical oxytrichid features like Oxytricha pattern undulating membrane, 18 frontoventral transverse cirri and fragmentation of dorsal kinety 3. Phylogenetic analyses supported non-monophyly of Cyrtohymena and other flexible-bodied oxytrichids.
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