The Life Cycle of the Histophagous Ciliate Tetrahymena corlissi Thompson, 1955*

SYNOPSIS The life cycle of Tetrahymena corlissi Thompson, 1955, is described from organisms fed on tissue of the oligochaete Enchytraeus. The trophont stage usually divides twice either while free‐swimming or encysted as a tomont. The tomont stage apparently occurs only when the trophont is removed from the “conditioned” tissue environment. The time to completion of division is constant and determined at the onset of exposure to tissue. The number of divisions is a function of the amount of tissue ingested. Tomites differentiate after the divisions as active theronts. This dispersal stage transforms to a trophont when tissue is ingested. If tissue is absent, the theronts become smaller, eventually settling on the substrate as immotile pyriform resting theronts, with a small proportion of the resting theronts encysting within a delicate cyst wall. When stimulated chemically or mechanically, the resting theronts transform to active theronts. If these active theronts ingest tissue, they transform to immature trophonts, initially incapable of division. Life cycle and morphologic dissimilarities among T. corlissi, T. bergeri , and T. rostrata are presently used to distinguish among these species.