Valves dorsiventral, with a convex dorsal margin, the ventral margin straight, sometimes gibbous or rarely convex, apices rounded or protracted, valves symmetrical to the transapical axis; frustules rectangular or slightly biconvex in girdle view.
Striae uniseriate, areolae often resolvable in LM, often with apically elongated external areolae openings (SEM), internally areolae open in depressions between virgae, often with short struts overlying the vimines, no hymenes or cribra. Stigmoids may be present at proximal end of central ventral striae near the raphe endings.
Raphe usually closer to the ventral margin, more or less straight, proximal endings slightly deflected to dorsal side, distal endings curved to ventral side, internally proximal raphe fissures deflected to dorsal side, iIntermissio present.
No apical pore fields; cells can live in mucilage tubes.
Chloroplast a single double H with a central pyrenoid, lying on the ventral side of the girdle.