Frustulia vulgaris

Valves are linear-lanceolate-rhomboid with rostrate and rounded apices. Areolae are round or oval and form transverse striae that are radiate at the center of the valve and slightly or strongly convergent near the apices. Striae are circumradiate about the apices. In SEM, a single row of isolated areolae next to either side of the raphe forms a continuous line. This line of areolae forms a boundary to the axial area and ovoid central area. The raphe branches are slightly curved. Internal, longitudinal ribs are parallel to the raphe. The longitudinal ribs fuse with the helictoglossae to form a porte-crayon structure, but are incomplete at the central nodule. The central nodule is relatively flat as compared to other Frustulia species. In SEM, the external proximal and distal raphe ends form a small Y-shape.