diatom


Also found in: Dictionary, Thesaurus, Medical, Wikipedia.
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.
..... Click the link for more information.
, 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.
..... Click the link for more information.
), 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.
..... Click the link for more information.
.

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).
..... Click the link for more information.
, 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 total diatom biomass was substantially (from 29% in April to 77% in June) higher in station DG1 than in station DG7 during all sampling occasions except for August when the diatom biomass observed in station DG7 exceeded that in station DG1 (Fig.
Distribution, ecology and nuisance effects of the freshwater invasive diatom Didymosphenia geminata (Lyngbye) M.
A total of 104 species of benthic diatoms from the 6 main rivers of Thailand were scored and listed in the Thailand diatom index.
We showed that the smaller of the two diatom daughters inherits more cellular material (or cytoplasm) from its parent, and subsequently grows faster and divides sooner than its larger sister.
Feeding concentrations for the diatom species (Navicula ramosissima) were determined using the methods of de la Pena (2007).
A total of 80 infrageneric diatom taxa were recorded from the tip-up pools (Table 1).
A striking feature in the post-isolation diatom stratigraphy from both studied lakes is distinct increase in freshwater planktonic diatoms that reaches 98% in the Kasmu and 92% in the Lohja record, respectively.
Indices that use diatom communities are more useful than physical and chemical measurements to assess water quality of rivers, particularly inorganic and organic pollutants.
The diatoms, which appear to thrive in the windier conditions, have increased in the last five years, while dinoflagellates have "almost disappeared", Prof Hays said.
Diatoms, who existence dates back to the time of dinosaurs, are single-celled organisms that rely on photosynthesis processing of the sun's rays as an energy source to live and reproduce.
1997, "Genetic variation in the diatom Fragilaria capucina along a latitudinal gradient across North America", Plant Syst.
Diatoms dominated under Nelumbo lutea; euglenophytes and small green algae dominated in turbid open-water regions.