Virga

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.

Alternative Terms

Interstria
Also described the silica between striae (Ross et al., 1979) but has been replaced by virga, which better describes the structure and morphogenesis of this valve feature.
Virga
Image Credit: Figure adapted from Round et al. (1990).
Diagram of a valve in the early stages of silica deposition. A single virga is indicated by the arrow. Virgae are the solid silica bands between the striae.