Natural and cultured variability of Engelmanniella mobilis (Ciliophora, Hypotrichida); with notes on the ultrastructure of its resting cyst

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Summary The variability of 2 Austrian populations (Gn, Bn), one Turkish (Tn), and one Japanese population (Jn) of the hypotrich ciliate Engelmanniella mobilis ( Engelmann , 1862) Foissner , 1982 is compared by morphological and morphogenetic analyses. These populations were isolated from soils and represent 2 groups (Gn, Bn, Tn; Jn) concerning some quantitative characters of the infraciliature, the morphology of the resting cyst, and some nuclear features during division. However, in cultures maintained for 3 months the variability of the Turkish population (Tc) increased markedly closing this gap. This demonstrates that morphological differences originating during cultivation might be greater than those observed in natural populations. The variability of our populations embraces E. halseyi ( Calkins , 1929) and E. mobilis americanus ( Kahl , 1932), which thus fall as junior synonyms of E. mobilis . During division and physiological reorganization the cortical events are identical in all populations, while the micronuclear processes may be slightly modified. Divisional and reorganizational morphogenesis differ in the origin of the frontal anlagen. The characterization of Engelmanniella Foissner , 1982 is improved. Young resting cysts of Bn, Tn, and Tc are characterized by a mucus layer originating from the extruded subpellicular granules. This layer is absent in older cysts and in the resting cyst of the Japanese population, although the subpellicular granules are released too. Oxytrichid (4-layered cyst wall, fused macronuclear segments) and urostylid (cortical microtubules) characters are mixed up in the resting cyst of E. mobilis, Kahliella simplex , and Paraurostyla weissei suggesting that the proposed classification of hypotrich resting cysts is premature.