Glossary terms starting with "v"


The intricately sculptured unit at each end of the diatom frustule. The broad surface displaying most of the ornamentation is called the face. The downturned surface that meets the cingulum is called the mantle.

The morphology of the valve provides many of the features used to classify diatoms.

Valve view

The view of the frustule when the valve is uppermost. See also girdle view.

Valvocopula - first girdle band

The copula, or girdle band, in direct contact with the valve. Accessory structures such as septa or partecta arise from the valvocopula.

See also cingulum.



Silica flap or porous plate covering an areola.

In a loculate areola, may form the external or internal wall, depending on species, opposite the foramen. Plural form is vela.

Two types of vela are cribra and volae.


The side of the valve face that is narrower and less convex than the dorsal side. Occurs in genera that are asymmetrical to the apical axis, such as Cymbella and Encyonema. From Latin for belly.



The crossbars that separate areolae within striae.


Virgae - Interstriae

The bars of silica located between striae.

Voigt discontinuity - Voigt fault, fault irregulare

An interruption in the stria pattern of a raphid diatom valve. The Voigt discontinuity, if present, occurs on the secondary side of a valve and marks the point of fusion of the sternum during ontogeny. Named for M. Voigt, who first noted it in 1943.


A flap of silica projecting from the side of a pore or from a bar crossing an areola. A type of velum. Plural form is volae.