Areola

An areola is a small opening (pore) that is regularly repeated in a diatom valve to comprise a stria. From Latin for small open space. Plural is areolae.

Areola is a general term for two groups of pores: chambered and unchambered. Electron microscopy is usually needed to resolve features of areolae. The type of areola can be important in diatom taxonomy.

(a) Unchambered areolae pass through a valve wall that has a single layer of silica. These areolae are usually covered by some type of occlusion and may appear in several forms: simple circular pores (raphid valve of many Cocconeis), oval, lineolate (Navicula), oblique slits, zig-zag lines (Delicatophycus delicatulus in this flora), curved, undulate, radiate (Cox 2004).

(b) Chambered areolae occur in valve walls composed of two separated layers of silica (Ross et al. 1979 p. 527 and Round et al. 1990 p. 30). The types of chambered areolae included here are alveolus, loculus, pseudoloculus, and false pseudoloculus. See each type for more detail.

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.