Live observation of excystment in the spirotrich ciliate Meseres corlissi

Excystment of Meseres corlissi Petz and Foissner 1992 was observed by light microscopy. Excysting cells were first recognized by the appearance of a non-pulsating vacuole. With increasing size of this vacuole, the outer cyst wall ruptured, creating a narrow slit. The emerging protoplast was enclosed by an inner flexible membrane. Oral membranelles were faintly visible, but inactive at this stage. Within the next hour, oral membranelles and a pulsating vacuole became active, and the ciliate started to rotate. During a phase of rapid movement, the flexible membrane became wider and thinner. Finally, it burst open and released the now fully differentiated ciliate. The emergence of M. corlissi from the cyst is similar to descriptions in the literature for Didinium nasutum, Nassula ornata, Tillina magna and several stichotrich ciliates.