ULTRASTRUCTURE OF CHRYSODIDYMUS-SYNUROIDEUS (SYNUROPHYCEAE)

A clonal isolate of Chrysodidymus synuroideus Prowse was derived from a Sphagnum bog in northern Wisconsin and maintained in culture for ove r 3 years. Cultured colonies consisted almost exclusively of two cells attached at the posterior, each cell bearing two unequal flagella. Co rrelative light and electron microscopic observations revealed that co lonies composed Of smaller, ovate cells represented more recent produc ts of cell division, while colonies of elongate cells were more mature . These results support previous taxonomic conclusions, based on light microscopic observations of field-collected specimens and body scale ultrastructure, that Chrysodidymus is a valid genus, and that two spec ies described by Prowse on the basis of cell size differences, should be merged. In addition, ultrastructural studies of cultured Chrysodidy mus demonstrated that this genus is a member of the Synurophyceae on t he basis of characters related to flagellar morphology, basal body arr angement, and cytoskeletal ultrastructure. Chrysodidymus synuroideus r esembles Synura sphagnicola in body scale structure, the presence of d istinctive linear or clavate scales on both flagella, a relatively loo se scale case, and acidophilic habitat. Unlike S. sphagnicola, Chrysod idymus has no pyrenoids, peripheral (rather than axial) plastids, and a single posterior storage vesicle (rather than two peripheral storage vesicles).