ABSTRACTPodochytrium dentatumoccurred during spring and fall on chitin bait placed in a Maine lake. Zoospore ultrastructure is of the chytridialean type and is a variant of theChytridiumsubtype. The zoosporangium forms from an apical expansion of the encysted zoospore. At maturity the dentate apical part of the zoosporangium, with orange contents, is separated from the basal part of the zoosporangium by a wall. Zoospores discharge in a mass surrounded by papillar material. Rhizoids branch from a knob-like rhizoidal base and are either fine or coarse.