All Taxa

: Hippodonta

Frustules linear, elliptic, lanceolate or rhombic in valve view, with acute, rounded or capitate poles.

Frustules isovalvar, isopolar and bilaterally symmetrical, strongly silicified; girdle depth variable, some species lying in valve or girdle view with approximately equal frequency, others having a deep girdle and more often lying in girdle view.

Striae uniseriate or biseriate; areolae apically elongate slits or (rarely) circular, occluded by hymenes at their inner apertures.

Axial area narrow; at the poles, a transapical thickening of silica forming polar bars. Central area variable, not differentiated from the axial area, expanded or a transverse fascia.

Raphe straight, with expanded, central and polar raphe endings.

Girdle composed of a broad, plain first band, and some narrower bands, all open.

Two plate-like chloroplasts per cell, one against each side of the girdle, as in Navicula.