THE OXYTRICHINA JANKOWSKI, 1980: MORPHOLOGY, MORPHOGENESIS, AND SYSTEMATICS (SPORADOTRICHINA, CILIPHORA, CYST)

The hypotrich suborder Oxytrichina Jankowski, 1980 is a poorly characterised, systematically ambiguous taxon. A lack of ultrastructural and developmental information on a variety of oxytrichine species resulted in the establishment of multiple and disparate systematic categorizations for these species. I chose 8 species for morphologic and developmental studies: Oxytricha fallax, Oxytricha quadrinucleata, Oxytricha similis, Stylonychia pustulata, Tachysoma sp., Gonostomum affine, Pleurotricha lanceolata, and Paraurostyla sp. I used light microscopy and SEM for the study of trophozoites and dividing cells, and TEM and SEM in my investigations of cysts. The major unifying developmental characteristic of the suborder is the production of longitudinal F-V-T streaks during division and reorganization. Encysting organisms resorb all kinetosomes and produce desiccation resistant cysts with 4 or 5 layered walls. Interspecific morphologic and developmental differences including presence of absence of multiple right marignal cirral rows and ventral longitudinal rows suggest recognition at at least 3 oxytrichine families: Oxytrichidae, Amphisiellidae, and Gonostomidae (n.fam.). I consider the family Amphisiellidae ancestral to the other 2 families. It is clear from previously published information that the families Keronidae and Kahliellidae share a common ancestry with the aforementioned 3 families and may be con-subordinal. A traditional view of interfamilial evolutionary relationships holds that the kahliellids, with multiple longitudinal rows of cirri, are primitive and perhaps ancestral to the rest of the suborder. I propose an alternative evolutionary scenario based upon a novel concept of somatic origin of the frontal ciliature. An ancestral hypotrich similar to Epiclintes with extensive ventral somatic ciliature and vanishingly scant frontal ciliature may have given rise to families with frontal ciliature increasing at the expense of somatic ciliature. In this second scenario, recognition of the frontal, and therefore relatively non-primitive origin of the ventral longitudinal rows of cirri necessitates disqualification of the kahliellids as ancestral to the amphisiellids, oxytrichids, and gonostomids