The phototactic zoospores of Nowakowskiella elegans (Nowak.) Schroeter and Cladochytrium replicatum Karling are similar in their ultrastructure and typical of the revised Chytridiales (Barr, 1980, Can. J. Bot. 58: 2380-2394). For a carbon source both species utilize cellulose, D-cellobiose, D-glucose, D-xylose, and D-mannose. Several sources of organic nitrogen, and inorganic nitrate, and ammonium are utilized. Both species are deficient for thiamine. Germination of the zoospore cyst in both cases is exogenous, and daughter nuclei migrate and divide independently in the developing rhizomycelium. Mitosis is intranuclear. Zoospore discharge in N. elegans is operculate and vesicular, and in C. replicatum inoperculate and vesicular. Resting spores are formed asexually in C. replicatum and sexually in N. elegans. Meiosis in N. elegans is described. Nowakowskiella and Cladochytrium are retained in the family Cladochytriaceae.

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