Chains straight, not twisted, usually short. Cells with elliptical valve surface and apical axis usually 8-12μm. Setae arising from the corners of the cell, without basal part. Apertures very narrow, slitlike. One type of intercalary setae thin, more or less curved, and usually turned toward chain ends. The other type heavy, almost club shaped, first straight and at a sharp angle from chain axis, then turning and running almost parallel to chain axis in outer part. Terminal setae more or less U-shaped, and differ from others in position, being first U shaped, then nearly parallel to chain axis in outer part. Chromatophore one in each cell, on girdle side.