All Taxa

Cymbellaceae: Cymbella

Valves dorsiventral, in valve view with a convex dorsal margin, and an often convex, rarely straight or concave ventral margin, apices rounded or protracted, valves symmetrical to the transapical axis; frustules biconvex in girdle view.

Raphe often more or less central, so raphe sternum variously curved. Internal and external raphe fissures not superimposed, external central raphe branches ventrally bent and recurved, terminal fissures deflected dorsally. External central raphe endings straight or deflected, often expanded. Internal central raphe ending hidden by an overgrowth of silica (intermission absent), internal polar helictoglossae often markedly thickened when apical pore fields present.

One or several isolated pores often present on ventral side of central raphe endings, often close to the ventral striae, internally occluded by irregular ingrowths.

Striae uniseriate, areolae often resolvable in LM, shape of external areola openings varies between species and can be important for identification; internally areolae open in depressions between virgae, no hymenes or cribra (SEM).

Apical pore fields often present, seen as clear areas on the ventral side of the polar raphe fissure.
Species with apical pore fields able to attach by mucilage stalks; without apical pore fields free living.

Chloroplast usually a single double H with a central pyrenoid, pyrenoid lying on the dorsal side of the girdle. Cymbella lanceolata has a single chloroplast with a central pyrenoid and many lobes coming off in different directions.