Morphogenesis of the division and encystment process of the ciliated protozoan Colpoda minima

We have investigated the main morphological features of the asexual division and encystment process in the ciliate Colpoda minima. It is a soil colpodid ciliate with a quite variable body size. The nuclear apparatus is composed of one ellipsoidal macronucleus and one lenticular micronucleus. The somatic infraciliature is made up of 69-101 kinetics, 10-16 of which are postoral. The oral infraciliature is made up of two oral polykineties, the left one consists of 45-60 short oblique rows of kinetosomes whereas the right one is formed by a row of kinetosome pairs and many short rows of kinetosomes disposed without a regular arrangement. Cell division occurs in a division cyst and produces four tomites. Stomatogenesis is merotelokinetal and involves about 16-23 stomatogenic kineties. A macronuclear extrusion process takes place during cell division. The resting cyst is included in the partial-kinetosome-resorbing (PKR) group, and its cyst wall has two layers which are derived from different cystic precursors. During encystment, macronuclear division and chromatin extrusion (in some cases) have been observed. All of these characteristics of the life cycle of C minima are compared and discussed with respect to those of other colpodid ciliates.