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The cell itself consists of two halves, each containing an essentially flat plate, or valve, and marginal connecting, or girdle band. One half, the hypotheca, is slightly smaller than the other half, the epitheca. Diatom morphology varies. Although the shape of the cell is typically circular, some cells may be triangular, square, or elliptical.
Bacterial motility is the ability of bacteria to move independently using metabolic energy. Most motility mechanisms that evolved among bacteria also evolved in parallel among the archaea. Most rod-shaped bacteria can move using their own power, which allows colonization of new environments and discovery of new resources for survival.
For many years the diatoms—treated either as a class (Bacillariophyceae) or a phylum (Bacillariophyta)—were divided into just 2 orders, corresponding to the centric and the pennate diatoms (Centrales and Pennales; alternative names Biddulphiales and Bacillariales, as used e.g. in Lee, 1989). [9]
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 microscopic layers of that shield appear to evolutionary biologists, "like they are composed of little tooth-like structures." [4] Neil Shubin writes: "Cut the bone of the [ostracoderm] skull open…pop it under a microscope and…you find virtually the same structure as in our teeth. There is a layer of enamel and even a layer of pulp.
Bacillaria paxillifer was originally described under the name Vibrio paxillifer by Otto Frederick Müller in 1786. It is the first diatom species known to be described. [5] It was separately described two years later (1788) by Johann Friedrich Gmelin as Bacillaria paradoxa.
Image credits: debdeman #6. Not me but my mother. My mom bought the travel insurance on her Disneyworld trip because she is bipolar and thought if she had a bad day they would get a refund.
A frustule is the hard and porous cell wall or external layer of diatoms. The frustule is composed almost purely of silica , made from silicic acid , and is coated with a layer of organic substance, which was referred to in the early literature on diatoms as pectin , a fiber most commonly found in cell walls of plants .