Isovalvar, isopolar or slightly heteropolar (one end may be slightly wider, or the ‘central’ expansion may be slightly closer to one end); bilaterally asymmetrical.
Cells deep, often with multiple girdle bands; consequently, when still intact, cells often lie in girdle view.
Valves often linear, with the central part and the valve ends swollen, or elliptic; in girdle view rectangular.
Striae uniseriate, parallel, irregularly spaced; small spines are often present between the striae at the junction of valve face and mantle; an apical pore field is present at each pole; a rimoportula is located near the valve centre, lateral to the sternum (axial area).
Axial area narrow.
Central area sometimes present and then often asymmetrical.
Girdle composed of several narrow bands, some of which bear prominent septa, visible in girdle view as longitudinal lines extending in from the cell apices (sometimes to near the centre); the septum-bearing bands are closed hoops, while other bands are open. Small pseudosepta can also be present.
Many short rod-like chloroplasts are scattered in the spaces between the septa and valves.
Cells form zig-zag (sometimes almost linear) or partly fan-like or stellate colonies.
Cells attach to each other or substrata by small mucilage pads secreted from the apical pore fields.