Mixotrophic plankton, which include the forms in Pyrrophyta, Xanthophyta, Euglenophyta, Cryptophyta, Chrysophyta, Chlorophyta and the Ciliophora of Protozoa, can be divided into three physiological types according to their nutrient strategy. The forms of Type I can grow well no matter which trophy they will take. The forms of Type II, i. e. heterotrophic microalgae, are generally phototrophic and sometime phagotrophic. The forms of Type III, i. e. autotrophic protozoa, are commonly phagotrophic and sometime...