Frustules curved, almost linear, with protracted apices and a small bulbous swelling at the centre on the concave side, rectangular in girdle view.
Frustules isovalvar, isopolar; bilaterally asymmetrical, usually lying in valve view because of their curvature; girdle fairly narrow.
Striae uniseriate, parallel (relative to the overall curvature of the cell), ghost striae in the central area; small spines may be present between the striae at the junction of valve face and mantle; an area of densely packed small pores (apical pore field) is present at each pole; a rimoportula is present at one or both poles, lateral to the sternum (axial area).
Axial area narrow. A prominent central area, hollow on the inside, is present, but only on the ventral (concave) side of the cell.
Girdle composed of several narrow bands.
One chloroplast per cell, containing a prominent pyrenoid located in and next to the hollow of the central area on the ventral side.