The diatom genus Sellaphora: Separation from Navicula

Abstract

The genus Sellaphora Mereschkowsky is resurrected to include those naviculoid diatoms with an H-shaped plastid containing an invaginated pyrenoid; a particular, characteristic series of conformational and positional changes in the plastid and nucleus during the cell cycle; gametangia that produce one gamete apiece and which remain closely associated throughout meiosis and plasmogamy, without any obvious mucilage envelope around them; physiological anisogamy, the single auxospore being formed within one gametangium and expanding parallel to its apical axis; small round poroids; and internal central raphe endings that are deflected towards the primary side of the valve. Light microscopical identification of Sellaphora is fairly straightforward if live cells are examined; cleaned valves require SEM observation. Many small “Navicula” species probably belong to Sellaphora; for the moment the species included are S. pupula (the type), S. americana, S. bacillum, S. disjuncta, S. laevissima, S. nyassensis, S. seminulum and S. vitabunda.