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Abstract
Ophrydium colonies were collected from a pond cypress swamp near Florala, Alabama and examined for diatoms. Observations of living colonies showed large numbers of motile diatoms with the ability to traverse the mucilage of the gelatinous ball. SEM observations indicated that diatoms were more concentrated on the surface of the protozoan colony than within. Although numerous, the diatoms were not taxonomically diverse (i.e. 10 species in 5 genera in cell counts). The most abundant species was Stenopterobia delicatissima (Lewis) Breébisson ex Van Heurck. The source of individuals colonizing the Ophrydium mucilage was leaf debris in the pond. However, S. delicatissima was 20 times more abundant in and on Ophrydium colonies than in debris. The diatom assemblage found is typical of an acidic, softwater situation and reflects the water chemistry of the cypress swamp. It is unlike the diatom assemblages collected from Ophrydium colonies elsewhere. However, it appears that the diatom floras of Ophrydium colonies are determined primarily not by the colony itself but by external factors such as water chemistry and climate. The new taxon Pinnularia gibbiformis var. floralensis var. nov. is formally proposed.