Valves asymmetrical to transapical axis (heteropolar) and symmetrical to apical axis. Cells usually wedge-shaped in girdle view with pseudosepta visible. Apices rounded to capitate. Raphe often slightly sinuous. A single stigma (occasionally more) usually present on one side of the central area. Striae often coarse. There is a single H-shaped chloroplast with a central pyrenoid.