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Diatoms of the United States is now known as Diatoms of North America.
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Glossary terms starting with "v"


The siliceous unit that lies at each end of the frustule. The two valves are linked by the girdle bands.

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.


A silica connection between adjacent virgae, separating areolae within a stria. Plural form is “vimines”. From Latin for “pliant twig”.

Virga - Interstria

The layer of silica between striae. Plural form is “virgae”. From Latin for “rod”.

The growth (morphogenesis) of pennate diatom valves with a single row of areolae in their striae resembles the making of a basket where the main supports were called virgae and the connections woven between them were called vimines. In diatoms, the virgae and the vimines join, creating the network of gaps which become the areolae (Cox and Ross, 1981).

See also costa.

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.