Diatom cells include an outer, siliceous cell wall which is composed of two parts, or valves. Many of the features used to classify diatoms are based on the morphology of the valves. Each valve has a face and a mantle.
Valve view refers to the perspective in which the valve face of a frustule is visible. An alternate view is girdle view, in which the frustule is viewed from the side.
The term for the girdle element that is in direct contact with the valve, the first girdle band. Accessory structures, such as septa, usually arise from the valvocopula.
A thin plate or flap of silica that covers the openings of loculate areolae; may be perforated with smaller openings
In diatoms that are asymmetrical to the apical axis, the ventral side is considered to be the side that is more narrow, as extending from the central sternum.
The Voigt discontinuities may be found on the secondary side of raphid diatoms. The Voigt discontinuities are interruptions in the striae that indicate the point where the silica of the valve was initially deposited. The Voigt discontiunity marks the point of fusion of the sternum.
Flap-like outgrowths (which originate) from the sides of pores or from bars crossing the areolae