The unusual, lepidosome-coated resting cyst of meseres corlissi (Ciliophora: Oligotrichea) : Encystment and genesis and release of the lepidosomes

Meseres corlissi Petz and Foissner (1992) is an oligotrichine ciliate covering the resting cyst with epicortical scales called lepidosomes. We studied in detail encystment as well as the genesis and release of the lepidosomes, using live observation, morphometry, and transmission electron microscopy. Encystment is remarkable in changing body shape distinctly and showing two phases of intense rotation. When encysting, the conical body becomes globular and forms a discoidal "head" via a fibrous ligament. Then, the cell rotates rapidly about its main axis for a minute. We speculate that this rotation transports the lepidosomes and cyst wall precursors to the cell's cortex. When rotation stops, the lepidosomes are released within about 5 - 20 s. Then occurs a second, slow rotation phase lasting several minutes and possibly distributing the material released by the cyst wall precursors. The lepidosomes develop in Golgi vesicles. Maturation thus occurs in a membrane-bound vesicle and is a complex process with seven distinct stages. The central cavity of the lepidosome develops asymmetrically, and the large meshes of the lepidosome wall develop earlier than the small ones. Growth of the lepidosomes does not occur by vesicular transport processes. The lepidosomes are released by classical exocytosis. The lepidosome (vesicle) membrane closes the port and becomes part of the newly forming cortex. Detailed data on encystment and lepidosome genesis are rare. However, it turned out that both, encystment and lepidosome genesis are more complex in M. corlissi than in most other ciliates.