Light microscopy observations on the encystation and excystation processes of the ciliate Phacodinium metchnikoffi (Ciliophora, Phacodiniidae), including additional information on its resting cysts structure

Abstract

The scope of our study presents a light microscopy study on the encystation, excystation and morphology of the resting cysts of the spirotrich ciliate, Phacodinium metchnikoffi. During the encystation process, the trophic cell changes in shape, size and volume, the horseshoe-shaped macronuclear nodule transforms into a compact rounded mass, the ciliature is resorbed and the cyst wall is formed. A characteristic accumulation of dark substances in the cell cytoplasm was observed. The most significant feature is the surface. Ornamentation in the form of protuberances in regular rows is located on the entire surface of the cysts. We also focused on the excystation process for the first time and uncovered several specifics of P. metchnikoffi excystation. The excystation is characterised by the formation of the excystation vacuole. An escape apparatus is also present. The coexistence of the excystation vacuole and apparatus during the excystation process is an unusual type of escaping and has not yet been described. The results suggest that not only the resting cysts surface, but also the excystation and encystation processes are much more varied than literary data indicate.