Valves clavate, rhombic, sometimes almost linear, sometimes with a gibbous centre, frustules in girdle view rectangular or wedge-shaped. Head pole wider than foot pole, rounded, (sub-)rostrate or capitate.
Valves asymmetrical to transapical axis (heteropolar) and symmetrical to apical axis.
Striae parallel to radiate, often coarse. Striae in the valve centre can be shortened and/or wider spaced. A single stigma (occasionally more) can be present on one side of the central area.
An apical pore field is present at the foot pole and bisected by the raphe.
Axial and central areas vary in width and shape: the axial area can be narrow linear, oval or broadly lanceolate, the central area can be absent, round, rectangular, an acute-angled fascia or subfascia, or it is asymmetrical due to the shortening or absence of the central striae on one side.
Striae uni- or biseriate with areolae small and round or c-shaped due to occlusion with reniform volae.
Raphe sternum straight and central, raphe straight or slightly sinuous. External proximal raphe endiungs often expanded, internally deflected or hooked towards the primary side of the valve; distal raphe fissure straight or sinuous.
Girdle consisting of several open bands with one or several rows of pores.
There is a single complex chloroplast with a central pyrenoid lying against one side of the girdle, linking two H-shaped plates lying below the valves.