Areola

An areola in a diatom valve is a regularly repeated pore that is not an elongated chamber (by contrast, an alveolus is an elongated chamber). From Latin for small open space. Plural is areolae.

Areola is a general term for two types of pores.

(a) Poroid areola, or poroid, which passes through a valve wall that has a single layer of silica (Ross et al 1979). A poroid areola is usually covered by some type of occlusion. Electron microscopy is usually needed to resolve occlusions (Round et al 1990 p. 30). Poroid areolae are illustrated here.

(b) Chambered areola, which is a regularly repeated opening in a valve wall that has two separated layers of silica (Ross et al 1979 p. 527 and Round et al 1990 p. 30). For the three types of chambered areolae, see loculus, pseudoloculus, and false pseudoloculus.

The type of areola can be important in diatom taxonomy. Some examples include simple poroid (raphid valve of many Cocconeis), lineolate (Navicula), punctate (Gomphoneis) and loculate (Diploneis).

Alternative Terms

punctum: A general term for a round or oval pore in the silica wall of a diatom. The plural is puncta.

Citations

N Tripunctata Lineolate Areolae — Valve of *Navicula tripunctata* (SEM). The arrow depicts one lineolate areola. These areolae are elongated in the apical direction, which is a characteristic of the genus *Navicula*. The areolae are arranged in rows to form the striae of the valve.

A Crassipunctata Areolae LM — Valve mantle of *Aulacoseira crassipunctata* showing many round areolae (LM).

A Crassipunctata Areola SEM — An areola of *Aulacoseira crassipunctata* with volae extending from its sides (SEM). Scale bar = 0.5 µm.