diatom


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Related to diatom: diatomaceous earth

diatom

(dī`ətŏm', –tōm'), unicellular organism of the kingdom ProtistaProtista
or Protoctista
, in the five-kingdom system of classification, a kingdom comprising a variety of unicellular and some simple multinuclear and multicellular eukaryotic organisms.
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, characterized by a silica shell of often intricate and beautiful sculpturing. Most diatoms exist singly, although some join to form colonies. They are usually yellowish or brownish, and are found in fresh- and saltwater, in moist soil, and on the moist surface of plants. They carry chlorophylls a and c and the carotenoid fucoxanthin contained in plastids. They reproduce asexually by cell division. Some 40,000 species (5,600 living species) are either bilaterally or radially symmetrical. For the most part they lack flagella. Although most diatoms are autotrophic, some heterotrophic or symbiotic species can be found in particular habitats. The living matter of each diatom is enclosed in a shell of silica that it secretes. These shells are marked by minute pores or depressions that allow the living organism access to its environment. As the principal constituent of plankton (see marine biologymarine biology,
study of ocean plants and animals and their ecological relationships. Marine organisms may be classified (according to their mode of life) as nektonic, planktonic, or benthic. Nektonic animals are those that swim and migrate freely, e.g.
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), diatoms are an important food source for fish and other aquatic animals, e.g., the baleen whaleswhale,
aquatic mammal of the order Cetacea, found in all oceans of the world. Members of this order vary greatly in size and include the largest animals that have ever lived. Cetaceans never leave the water, even to give birth.
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.

When aquatic diatoms die they drop to the bottom, and the shells, not being subject to decay, collect in the ooze and eventually form the material known as diatomaceous earth (sometimes called kieselguhr). When it occurs in a more compact form as a soft, chalky, light-weight rock, it is called diatomite. Deposits of diatomaceous material, formed underwater in past geologic time and now exposed above water, are found in all parts of the world. Diatomite is much used as an insulating material against both heat and sound, in making dynamite and other explosives, and for filters, abrasives, and similar products. Most of the earth's limestone has been deposited by diatoms, and much petroleum is of diatom origin.

Diatoms are classified in the phylum (division) ChrysophytaChrysophyta
, phylum (division) of unicellular marine or freshwater organisms of the kingdom Protista consisting of the diatoms (class Bacillariophyceae), the golden, or golden-brown, algae (class Chrysophyceae), and the yellow-green algae (class Xanthophyceae).
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, class Bacillariophyceae.

diatom

[′dī·ə‚täm]
(invertebrate zoology)
The common name for algae composing the class Bacillariophyceae; noted for the symmetry and sculpturing of the siliceous cell walls.
References in periodicals archive ?
The relationship of the distribution of the diatom Skeletonema tropicum to temperature.
depth, salinity, pH, trophic status) and each diatom species has its optimum and tolerance limits for different environmental variables (Van Dam et al.
Subsamples for grain size analysis and diatom examination were prepared together and treated to remove all organic material and carbonates.
Considering the lack of ecological information on large rivers, this study aims to conduct the following: i) evaluate the temporal and spatial variation of planktonic diatoms in terms of abiotic variables and the trophic level of the river water upstream and downstream of the Iguassu falls in the Iguassu River; ii) and select diatom descriptors of the physical and chemical conditions of the water in these two sampling stations and identify factors determining the community structure.
Quantifying species indicator values for trophic diatom indices: a comparison of approaches.
The association of multivariate analysis (abiotic variables and composition and structure of the periphytic diatom assemblage) was examined by means of the Procrustes analysis (PERES-NETO; JACKSON, 2001).
In order to cover the productive season when diatom forming and retaining by dams occur, the sampling started in April and ended in November.
When the XHY complex breaks apart, its energy is distributed among the different degrees of freedom of the resulting diatom and single atom.
Is there any difference other than size between two diatom daughter cells, and if so, which daughter cell does better?
Also silver bioaccumulations in epipelic diatom frustules of Yoncali Village (after discharge of mine) were significantly higher than uncontaminated stations (an average of 7 times).
Only a few studies are reported dealing with diatom flora of Lakes in Pakistan (Leghari et al.