Morphology of four plagiogrammacean diatoms; Dimeregramma minor var. nana,Neofragilaria nicobarica,Plagiogramma atomus and Psammogramma vigoensis gen. et sp. nov., and their phylogenetic relationship inferred from partial large subunit rDNA

A marine araphid pennate diatom obtained from sand grains sampled at two sites at Vigo, Spain is described as Psammogramma vigoensis S. Sato et Medlin, a member of the family Plagiogrammaceae, based on observations of frustule fine structure. The species possesses elongated valves with apical pore fields and parallel rows of striae oriented perpendicular to the apical axis. Valve poroids are occluded by perforated rotae. There is a weak sternum along the apical axis and rimoportulae are absent. Detailed observations of Dimeregramma minor var. nana (Gregory) Ralfs, Neofragilaria nicobarica Desikachary, Prasad et Prema and Plagiogramma atomus Greville, were also undertaken. Based on morphological features, the transfer of Neofragilaria nicobarica from the Fragilariaceae to the Plagiogrammaceae is proposed. Partial large subunit rDNA phylogeny also supported inclusion of both Psammogramma and Neofragilaria in Plagiogrammaceae.