Ultrastructure of the mycophagous ciliate Grossglockneria acuta (Ciliophora, Colpodea) and phylogenetic affinities of colpodid ciliates.

Ultrastructural features of Grossglockneria acutaFoissner, 1980 are very similar to those known in the confamilial species, Pseudoplatyophrya nana. The somatic infraciliature corresponds to the typical colpodid dikinetid pattern. The peculiar oral apparatus is described in detail. The feeding tube contains about 17 concentric cytostomial microtubular lamellae and postciliary microtubules. The lamellae are interconnected by dense plaques and their innermost microtubules anchor in dense material at the distal end of the tube. The postciliary ribbons of the paroral kinetosomes extend subpellicularly into the proximal region of the tube. It is supposed that supernumerary postciliary microtubules are proliferated and assemble to the cytostomial microtubular lamellae during stomatogenesis. Few transverse microtubules are associated to some adorai and presumably all paroral kinetosomes; they do not extend into the tube. Most basal bodies of the single adorai organelle lack kinetosomal derivates. The Grossglocknerida and Colpodida are suggested to be sister groups because they undergo a telokinetal stomatogenesis in reproductive cysts. The colpodid kinetid is characterized by a compound microtubular structure of posterior transverse ribbons to the left of the kinety. Several hypotheses as to the origin of the typical colpodid kinetid pattern, especially the posteriorly extending transverse microtubules, are discussed. Available evidence suggests haptorid or nassulid ancestors of the colpodids. Some data indicate a paraphyletic composition of the class.