Phycokey - Biraphe pennate diatoms










The raphe is a slit through a valve that enables movement of the frustule along a substrate. Biraphe diatoms have one raphe on each valve, monoraphes have one raphe on just one valve. The mechanism of movement includes extrusion of mucilaginous threads from the plasmalemma and through the raphe, that attach to the substrate. These are moved along the raphe, propelling the frustules in the opposite direction. At the end of the raphe the threads apparently detach from the frustules, leaving a trail behind.
Sketch by Golobova Diatoms with one or two raphes: Movement on a substrate. Schematic diagram of a biraphe diatom moving on an irregular surface (M.A. Golobova). Microfilaments attach to the substrate and are moved to the left in these sketches until they reach the end of the raphe, when they apparently detach from the frustules. The microfilament movement propels the frustule to the right. The entire movement can be reversed under the influence of any of several physical and/or chemical factors including light, temperature, pH, etc. enabling the diatom to move toward optimal conditions.