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Diatoms are classified as eukaryotes, organisms with a nuclear envelope-bound cell nucleus, that separates them from the prokaryotes archaea and bacteria. Diatoms are a type of plankton called phytoplankton, the most common of the plankton types. Diatoms also grow attached to benthic substrates, floating debris, and on macrophytes.
These patterns are composed of a series of transverse lines (known as striae) that can appear as rows of dots when viewed with an optical microscope. 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.
Thalassiosira pseudonana is a species of marine centric diatoms.It was chosen as the first eukaryotic marine phytoplankton for whole genome sequencing. [1] T. pseudonana was selected for this study because it is a model for diatom physiology studies, belongs to a genus widely distributed throughout the world's oceans, and has a relatively small genome at 34 mega base pairs.
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Pleurosigma is mainly a benthic genus of diatoms, whose cells are several times longer than they are wide. They present bright green chloroplasts observed in the shape of ribbons under a microscope. The central nucleus composes the core of the cytoplasm.
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 ...
Views of the centric diatom Coscinodiscus wailesii Light micrographs of a living cell in face view (a) and side view (b); many small discoid chloroplasts are visible. FESEM micrographs of a cleaned single valve, inner view (c) and outer view of a complete theca (d).