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Diatoms can be obtained from multiple sources. [86] Marine diatoms can be collected by direct water sampling, and benthic forms can be secured by scraping barnacles, oyster and other shells. Diatoms are frequently present as a brown, slippery coating on submerged stones and sticks, and may be seen to "stream" with river current.
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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.
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.
The Coscinodiscophyceae are a class(s) of diatoms. [1] They are similar to the Centrales, a traditional, paraphyletic subdivision of the heterokont algae known as diatoms. [2] [3] [4] The order is named for the shape of the cell walls (or valves or frustules) of centric diatoms, which are circular or ellipsoid in valve view.
Fragilaria is a genus of freshwater and saltwater diatoms. It is usually a colonial diatom, forming filaments of cells mechanically joined by protrusions on the face and in the center of their valves. The individual diatoms appear swollen in their centers where they are joined to the colonial ribbon. [1]
When its size becomes too small, a dividing diatom cell produces an auxospore to expand its cell size back to that which is normal for vegetative cells. [ 2 ] Auxospores can also play a role in sexual reproduction in diatoms, and may be formed after haploid gametes fuse to form a diploid zygote .