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Abstract
The marine gomphonemoid diatom originally described as Gomphonema margaritae Frenguelli & Orlando 1958, was studied with the light and scanning electron microscopes based on original material and recent samples collected in rocky substrates of the Elephant Island, Antarctica during the Brazilian Antarctic Expedition (PROANTAR XIII, November 1994).
This species was invalidly published as Gomphonema margaritae Frenguelli & Orlando by lacking Latin description and type designation. Original material of Gomphonema margaritae Frenguelli & Orlando collected from Esperanza Bay in January 1952 was analyzed and compared in the light microscope with material from Elephant Island. The comparison allowed us to determine that both materials contained the same species. We therefore validate Frenguelli & Orlando's taxon by providing a Latin description and designating the holotype and we transfer it to the genus Tripterion Holmes, Nagasawa & Takano as Tripterion margaritae (Frenguelli & Orlando ex Fernandes & Sar) Fernandes & Sar. Since there was no unmounted sample in Frenguelli & Orlando's original material, only the recent collection was examined in the electron microscope. Cells are attached to the substrate by means of mucilage threads secreted at the foot pole. Valves are heteropolar, with raphe system bearing angular bent terminal fissures, and with several closer striae at the foot pole similar in appearance to an apical pore field. Cingulum has four open bands, two bearing well developed septum opposite each other. The species was further compared with the two extant Tripterion species, and the inclusion of Tripterion in the family Rhoicospheniaceae was proposed.