Brackish-water and fresh-water species of the diatom genus Skeletonema Grev. I. Skeletonema subsalsum (A. Cleve) Bethge

Type material of Skeletonema subsalsum has been examined by light and electron microscopy. The species belongs to Skeletonema and is not conspecific with Stephanodiscus subsalsus. Skeletonema subsalsum is distinguished from S. costatum morphologically mainly by structure of connecting processes, those of S. subsalsum being tubular with a basal circular hole while those of S. costatum are trough-shaped with a wide basal opening. In addition to the Stockholm Archipelago (type locality), S. subsalsum was recorded from the Gulf of Finland and the river Wümme in the Bremen area.