Cortical morphogenesis during encystment in a ciliate, Euplotes encysticus Yonezawa, 1985

Cortical morphogenesis occurring during encystment was described on the silver impregnated specimens of Euplotes encysticus. During encystment, the ventral cortex of the cell invaginated into the cytoplasm together with the ventral ciliatures at 3 areas, resulting in a reduction of ventral surface. The invagination of the ventral cortex resulted in 3 gaps in the argyrome, which served as the indicators of ventral surface of the cysts. Dorsal bristle rows did not invaginate but remained on the cell surface of the cyst, except for DR 1 which invaginated into the cytoplasm together with AZM, and served as indicators of the dorsal surface of the cyst. Dorso-ventral swellings, which have been observed during encystment of oxytrichid ciliates, did not occur. These findings together with the results of earlier papers suggest that hypotrich cysts should be classified into at least 3 types, 1) Oxytricha-type, 2) Urostyla-type, and 3) Euplotes-type, and that Euplotidae may occupy a phylogenetically distant position to other traditional hypotrichs.