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Some pennate diatoms also exhibit a fissure along their longitudinal axis. This is known as a raphe, and is involved in gliding movements made by diatom cells; motile diatoms always possess a raphe. In terms of cell cycle , vegetative cells are diploid and undergo mitosis during normal cell division .
Some pennate diatoms are capable of a type of locomotion called "gliding", which allows them to move across surfaces via adhesive mucilage secreted through a seamlike structure called the raphe. [60] [61] In order for a diatom cell to glide, it must have a solid substrate for the mucilage to adhere to.
Navicula diatoms are highly motile and move through a gliding movement [3] [4] [5] This is done through excretion of extracellular polymeric substances (EPS). One form of EPS surrounds the outside of the cell and another is excreted through a slit in the frustule called a raphe, allowing the cell to glide along a track.
Medlin and co-workers erected a new class, Mediophyceae (which could be re-ranked a subclass if diatoms as a whole are ranked as a class rather than a phylum) for the "polar centric" diatoms, which they consider to be more closely related to the pennate rather than to other centric diatoms, a concept which has been followed or further adapted ...
The diatom lineage may go back 180 to 250 million years ago (Mya). About 65 Mya, diatoms survived a mass extinction in which roughly 85% of all species perished. [6] Until 1994, the genus was known as Nitzschia, but was changed to Pseudo-nitzschia because of the ability to form chains of overlapping cells, as well as other minor morphological differences. [8]
Fragilariopsis cylindrus is a pennate raphid diatom with a retangular cell with an elongated apical valve ranging from 15 to 55 μ and a transapical axis ranging from 2.4 to 4 μm. [9] Like other diatoms, F. cylindrus presents a cell wall composed of two biogenic silica valves, the frustule. It is also possible to note the presence of an ...
Asterionella average cell size is 60–85 micrometers long and 2–4 micrometers wide. It forms colonies that often consist of eight cells, but can vary up to 20 cells. The cells in the colony are attached by the apex by extracellular matter. By the way the cells are attached to each other, the colonies often look like stars or spiralling chains.
As the diatom divides, each daughter retains one theca of the original frustule and produces one new theca. This means that one daughter cell is the same size as the parent (epitheca and new hypotheca) while in the other daughter the old hypotheca becomes the epitheca which together with a new and slightly smaller hypotheca comprises a smaller ...