Description of Oxytricha
Species of this hypotrich ciliate are 40 to 260 microns long and are flexible. The genus is elongated, ovoid and dorso-ventrally flattened, with a flat ventral surface and arched dorsal surface. The oral cavity expands from the cytostome anteriorly. A pronounced adoral zone of membranelles extends from the cytostome along the left side of the cell and across the anterior end of the cell. The genus is very similar to Cyrtohymena and Notohymena. Two undulating membranes (one paroral and one endoral membrane) follwing a slightly curving path along the right side of the oral depression; in ventrally viewed silver stained cells the kineties of these two membranes usually cross. There are two marginal rows of somatic cirri which are not continuous at the posterior. The genus exhibits the typical oxytrichid ventral cirri pattern (8 frontal, 5 ventral and 4 or more transverse cirri). Usually, three caudal cirri extend from the posterior end. Typically two macronuclei are located in the central of the cell.