The valvar ultrastructure of the diatomGomphonema septumMogh. was investigated with scanning electron microscopy and is discussed with regard to the taxonomic position of this species. Ultrastructural features include striae composed of double rows of puncta, presence of a narrow axial plate which is responsible for the image of longitudinal lines, and apical pore fields composed of pores dissimilar in appearance from the puncta. These and other ultrastructural characteristics point to a close relationship betweenG.septumand members of the genusGomphoneis. A transfer ofGomphonema septumtoGomphoneisis proposed. Information supplemental to previous observations on the size range and variability of this species is presented.
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