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.
One or two slits, or fissures, through the valve face of
diatoms. If two slits are present, each is called a branch of the raphe. Branches may be separated by a silica thickening called the central nodule. Raphe position may be axial, along the
; eccentric, along one margin; or circumferential, around the whole margin of the valve. From Greek for seam.
The raphe is the structure that the diatom cell uses to move over surfaces.
A thin, elevated structure, with the shape of the letter T, that extends along the lateral side of the raphe.
Compared to a conopeum, a raphe ledge is more elevated, more narrow, and does not cover part of the valve face. Common in the genus Amphora and closely related genera.
The valve of a monoraphid pennate diatom lacking a raphe.
The proximal internal terminations of the raphe in a rectangular, elevated, elongate structure. This structure is found in Muelleria, Scoliopleura and Neidium.
A structure that is bent back on itself.
A rhombus is a geometric shape, a type of parallelogram. The opposite sides of a parallelogram are equal in length, while a rhombus is a type of parallelogram with all four sides of the same length. Diatom valves, or their central area, may be described as similar to a rhombus, or rhomboid.
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.
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.
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.