Cells spicular, linear to linear lanceolate in valve view, with rounded, protracted, rostrate to subcapitate ends; cells lying in valve or girdle view.
Isovalvar, isopolar, bilaterally symmetrical.
Striae uniseriate, parallel, perpendicular to apical axis, distinctly punctate in LM; areolae circular or almost rectangular, aligned apically as well as transapically (‘orthostichous’ striae), occluded externally by cribra. At each end there is a rimmed area (apical pore field) of closely spaced, small, unoccluded pores; adjacent to the pore field there is a single rimoportula.
Axial area narrow, linear. Central area large, rounded or rectangular extending to both valve margins (forming a fascia), hollow on the inside, creating a lens-like appearance in LM.
Girdle structure unknown.
Chloroplasts large, plate-like (number unknown).
Cells usually forming tuft-like colonies attached to surfaces by individual mucilage pads secreted through the apical pore fields, or by a massive compound sheet of mucilage produced by a line of several or many adjacent cells (derived from a single cell by repeated division).