The ultrastructure of Commation gen. nov. (Stramenopiles incertae sedis), a genus of heterotrophic nanoplanktonic flagellates from Antarctic waters

Commation gen. nov. is a genus of planktonic, unicellular protists characterized by a circular to oval (sometimes flattened) cell body and a proboscis. Cells move predominantly by gliding. The mitochondria are tubulocristate and the two flagellar basal bodies are furnished with microtubular roots as well as a rhizoplast. The single emerging flagellum, which is rarely observed, apparently carries tripartite hairs. These features suggest that Commation should be listed among the genera and groups of organisms assembled in the informal group stramenopiles. Two species, C. eposianum sp. nov. (previously referred to as the "comma-shaped amoeba") and C. cryoporinum sp. nov., are described from Antarctic waters. The species are distinguished by differences in, e.g., the morphology of the proboscis, the complexity and details of the cytoskeleton, and the number of types of extrusomes present. Commation spp. appear to be ubiquitous in Antarctic waters at cell abundances typically ranging from 10-3-10-4 cells per litre.