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).

See also occlusion and alveolus.

Alternative Terms


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

N Tripunctata Lineolate Areolae
Image Credit: Marina Potapova
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
Image Credit: Marina Potapova
Valve mantle of Aulacoseira crassipunctata showing many round areolae (LM).
A Crassipunctata Areola SEM
Image Credit: Marina Potapova
An areola of Aulacoseira crassipunctata with volae extending from its sides (SEM). Scale bar = 0.5 µm.