Frustules linear or linear-elliptical in valve view, dorsiventral, with an undulate ventral margin and a convex dorsal margin and rounded poles.
Frustules isovalvar, isopolar and bilaterally asymmetrical; cells lying in valve or girdle view.
Striae uniseriate or biseriate, parallel; areolae circular, occluded by more or less reniform flaps; at the poles, on the ventral side of the frustule there are areas (pore fields) of densely packed small pores, through which mucilage is secreted.
Axial area narrow. Central area wide, especially on the ventral side; on the dorsal (primary) side or almost exactly centrally, there is a single isolated pore (stigma).
Raphe slightly sinuous, slightly expanded central endings externally, hooked endings at the centre internally, and terminal fissures hooked towards the ventral (secondary) side.
Girdle composed of open bands.
One complex chloroplast per cell, consisting of two X- shaped plates against the valves, connected by a substantial bridge on the secondary side of the cell (i.e. on the ventral side, on the opposite side to the stigmata) containing a prominent pyrenoid.