MORPHOLOGY AND ECOLOGY OF THE COSMOPOLITAN CILIATE PRORODON VIRIDIS

Descriptions are provided of the morphology, infraciliature, life cycl e, and ecology of the freshwater ciliate Prorodon viridis. P. viridis is a prostomatid ciliate with endosymbiotic Chlorellae and with a cosm opolitan distribution. The ciliate lives close to the oxic-anoxic boun dary in freshwater lakes and ponds worldwide, and it is able to surviv e in anoxic, dimly-lit deep waters. The O-2-evolving endosymbionts - t he zoochlorellae - probably sustain the aerobic respiration of the cil iate host. The vertical distribution of this species in natural oxygen gradients is described.