diatom

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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 ?
Para la filtracion de la cerveza se utilizo el equipamiento disponible de filtro placa con membranas de celulosa con una permeabilidad de 1 [micron]m y se utilizaron tierras de diatomeas como precapa [2].
Los cristales, granos de polen y diatomeas se observaron exclusivamente en el sector de tubo e insercion tubo-hornillo.
En la zona austral de Chile, las diatomeas son predominantes en los ensambles fitoplanctonicos (Iriarte et al, 2001, 2007; Alvez-de-Souza et al, 2008).
2012), en el cual se registran 87 especies de microalgas en la columna de agua; seis de ellas reconocidas como dominantes (cuatro diatomeas y dos dinoflagelados).
22) registraron esta especie en la Peninsula Iberica y Francia, consideran que se trata de una especie invasora de origen tropical o subtropical, que ha mostrado una rapida dispersion probablemente debida a su capacidad de aclimatacion al igual que otras diatomeas de origen tropical en las aguas europeas.
Por tales motivos, se planteo como objetivo de la presente investigacion evaluar los efectos ecotoxicologicos de los hidrocarburos de petroleo (petroleo crudo, el Diesel 2 y el kerosene) sobre el crecimiento poblacional de la diatomea Chaetoceros gracilis y determinar la concentracion efectiva media (CE50%).
Esta diatomea perteneciente a la familia Rhaphonedaceae es de pequeno porte con promedio de 12 [micron]m y tamano 12 x 4 [micron]m (Figura 1B y C).
Mas dificil de valorar es su contribucion original: publico, entre 1941 y 1946, algunos estudios taxonomicos sobre diversas especies de fitoplancton y de diatomeas, (60) grupos complejos a los que se habia dedicado ocasionalmente en Espana (61) y que en Mexico apenas habian merecido, hasta entonces, la atencion de los botanicos.
Phat es una diatomea unicelular que no tiene valvas de silice y que esta empezando a ser utilizada para enriquecedor el contenido de EPA en artemia y rotiferos (Okauchi & Tozuda 2003).