Morphogenesis and ultrastructure of the soil ciliate Engelmanniella mobilis (Ciliophora, Hypotrichida).

The morphogenetic pattern, freeze-fracture, transmission, and scanning electron-microscopy of interphasic cells were used to elucidate the enigmatic systematic position of Engelmanniella mobilis. Frontal, buccal, parabuccal, and marginal cirri are distinguishable during cortical development; transverse, frontoterminal (migratory), and caudal cirri are absent. Ontogenetic peculiarities include the conservation of parental and grandparental marginal cirri and the apokinetal origin of a dorsal kinety in the opisthe. Thus, interphasic cells of E. mobilis possess three generations of cirri. The pellicle is multilamellated. Prominent, undischargeable subpellicular granules consisting of a homogeneous osmiophilic mass develop from bundles of long fibers. Rhomboid crystal-like structures projecting from the lithosomes and regularly patterned mitoribosomes are additional remarkable ultrastructural characteristics. The somatic and frontal cirri comprise 2-10 kinetosomes. Very likely, all cirri are composed of closely adjacent "dikinetids" because their kinetosomes form pairs each possessing a transverse and a postciliary microtubular ribbon. The fourth row of kinetosomes of the adorai membranelies shows the usual transverse microtubular ribbons, while one or two transverse microtubules are closely adjacent to the third and the second row of its basal bodies. Our data suggest that Engelmanniella has descended from a kahliellid lineage. However, its placement in a well-founded (!) stichotrichid family is impossible at present.