Raphe

The term, raphe, refers to an opening, or slit, within the silica cell wall. The raphe system includes the slit and the mucilaginous material that is secreted from the cell and used for cell motility.

The raphe is composed of one or two slits that penetrate the valve of some 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. The raphe position may be (1) axial, along the apical axis; (2) eccentric, along one margin; or (3) circumferential, around the whole margin of the valve.

In this flora, three types of axial raphe are recognized. The terminology is simplified and species often possess more complex structures. (1) A simple raphe refers to a straight (filiform) or undulate raphe. The slit is positioned perpendicular to the valve face. (2) A lateral raphe refers to a slit that passes through the valve at an oblique angle. Under LM, the external and internal openings of the slit are both visible. The lateral raphe may be perpendicular near the proximal and distal ends. (3) A complex raphe refers to slits that undulate from side to side, one or more times. The genus Pinnularia often has species with a complex raphe.

The term originates from Greek for "seam".

Alternative Terms

raphe system

Citations

N Tripunctata Raphe — This SEM image shows the two branches of the raphe system on a single valve of *Navicula tripunctata*. This is a biraphid diatom, meaning both valves of a frustule possess a raphe system. This valve has a simple raphe.

K Clevei Raphe Lm — This light microscope image shows the two branches of the raphe system on the raphe valve of *Karayevia clevei*. This is a monoraphid diatom, meaning that only one valve of the frustule has a raphe system. This valve has a simple raphe.

K Clevei Internalraphe — This SEM image of the inner side of the raphe valve of *Karayevia clevei* shows that the raphe is open to the interior of the cell. This valve has a simple raphe.