Spontaneous and heat shock-induced irregularities in the cell structure of Didinium cf. nasutum

Deviations of the normal morphology and arrangement of the ciliary girdles and of the dorsal brushes of Didinium cf. nasutum are documented by SEM. Additionally, irregular fission stages such as symmetrical doublets which possess two parallel or antiparallel probosces are found in normal cultures. These ciliates are relatively long-lived (about one month). The didinia with oppositely oriented probosces feed continuosly on paramecia and produce normal cells which are indistinguishable from type-cells under a light microscope . Didinia with three or four probosces were not viable for longer than one to two weeks. All types of irregular forms could be induced experimentally by a 15-min exposure at 30 °C of cells cultured at 18 °C.