Rhizophlyctis harder is a questionable member of the genus Rhizophlyctis, and more stable and reliable characters are needed to establish the taxonomic position of this chytrid. As a source of such characters the flagellar apparatus of zoospores of R. harderi was reconstructed from serial sections, and the precise configuration was determined. The flagellar apparatus included two major microtubular roots, each with separate points of origin near the kinetosome. Root A extended laterally from one side of the kinetosome toward and around one rumposome and then continued anteriorly. The other, root B, originated between the kinetosome and secondary centriole near fibrillar connecting material and projected anteriorly into the cytoplasm. Each of these two major roots branched into two rootlets. This system of microtubular roots is more complex than that found in the flagellar apparatus of other Chytridiomycetes presently described. The structure of the flagellar apparatus and accompanying roots clearly separates this species from others in the genus Rhizophlyctis and indicates that it can be used to establish a new genus in the Chytridiales. Key words: Rhizophlyctis harderi, Chytridiales, zoospores, flagellar apparatus, ultrastructure.