Glossary terms starting with "r"

Radiate

Striae that lean away from the central nodule, with the sternum as the origin. Radiate, or divergent, striae may occur throughout the valve, only at the valve center, or only at the valve apices. In contrast, striae are convergent if they lean toward the central nodule, with the sternum as the origin.

Raphe

A slit through the valve face of monoraphid and biraphid diatoms. Usually positioned along the apical axis, or on a keel. The raphe, or raphe system, is the structure that the diatom cell uses to move over surfaces. From Greek for seam.

Rapheless valve - pseudoraphe valve, PRV, central sternum

The valve of a monoraphid pennate diatom lacking a raphe.

Rectelevatum

The proximal internal terminations of the raphe in a rectangular, elevated, elongate structure. This structure is found in Muelleria, Scoliopleura and Neidium.

Recurved - reflexed

A structure that is bent back on itself.

Rimmed depression - hufeisen

A hyaline depression on the inside of a valve. It occurs only in some species of the genus Planothidium and is a depression of the asymmetrical central area on the rapheless valve. See also hood.

Rimoportula - labiate process, jelly pore

A tubular process on the valve of some diatoms. On the internal valve face, the rimoportula opening has the shape of a pair of lips. On the external valve face, the rimoportula opening may be a simple, round aperture at the valve surface or it may be a tube extending out from the valve. Plural form is rimoportulae.

Rimoportulae are found in centric genera such as Stephanodiscus and Aulacoseira; in araphid genera such as Diatoma, Hannaea, Meridion and Tabellaria; and in eunotioid genera such as Actinella, Amphorotia, Eunophora, and Eunotia.

Rimoportulae extrude polysaccharides and other carbon compounds. They are considered to have appeared relatively early in diatom evolution, but to have been lost in a number of more advanced, raphid groups.

Ringleiste - sulcus

An internal, silica ledge that projects into the cell interior from the collum. The ringleiste is found only in the genus Aulacoseira and is variously developed in different species of the genus.

Rostrate

Valve end, or apex, having the shape of a beak, or rostrum. See also capitate.