diatom


diatom
/duy"euh teuhm -tom'/, n.
any of numerous microscopic, unicellular, marine or freshwater algae of the phylum Chrysophyta, having cell walls containing silica.
[1835-45; < NL Diatoma orig. a genus name, fem. n. based on Gk diátomos cut in two. See DIA-, -TOME]

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Any member of the algal division or phylum Bacillariophyta (about 16,000 species), tiny planktonic (see plankton), unicellular or colonial algae found floating in all the waters of the earth.

The intricate and delicate markings of the silicified cell wall are useful in testing the resolving power of microscope lenses. The beautiful symmetry and design of diatoms justify their title "jewels of the sea." Among the most important and prolific sea organisms, diatoms serve directly or indirectly as food for many animals. Diatomaceous earth, composed of fossil diatoms, is used in filters, insulation, abrasives, paints, and varnishes, and as an insecticide.

Diatom (highly magnified)

Eric Grave
Photo Researchers

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▪ algae class
  any member of the algal class Bacillariophyceae (division Chromophyta), with about 16,000 species found in sediments or attached to solid substances in all the waters of the Earth. Diatoms may be either unicellular or colonial. The silicified cell wall forms a pillbox-like shell (frustule) composed of overlapping halves (epitheca and hypotheca) perforated by intricate and delicate patterns useful in testing the resolving power of microscope lenses.

      During reproduction, usually by cell division, the overlapping shell halves separate, and each secretes a (usually) smaller bottom half. Thus, individual diatoms formed from successive bottom halves show a progressive decrease in size with each division. In a few months there can be as much as a 60 percent decrease in average size. Periodic spore formation serves to restore the diatom line to its original size.

      Diatoms are divided into two orders on the basis of symmetry and shape: the round, nonmotile Centrales have radial markings; the elongated Pennales, which move with a gliding motion, have pinnate (featherlike) markings. Food is stored as oil droplets, and the golden-brown pigment fucoxanthin masks the chlorophyll and carotenoid pigments that are also present. Diatoms, among the most important and prolific microscopic sea organisms, serve directly or indirectly as food for many animals. Diatomaceous earth, a substance composed of fossil diatoms, is used in filters, insulation, abrasives, paints, and varnishes and as a base in dynamite.

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Universalium. 2010.

Look at other dictionaries:

  • Diatom — Di a*tom (d[imac] [.a]*t[o^]m), n. [Gr. dia tomos cut in two. See {Diatomous}.] 1. (Bot.) One of the {Diatomace[ae]}, a family of minute unicellular Alg[ae] having a siliceous covering of great delicacy, each individual multiplying by spontaneous …   The Collaborative International Dictionary of English

  • Diatōm — (v. gr., Miner.), was nach einer Richtung leicht theilbar ist; z.B. Diatomischer Schillerspath, so v.w. Schillerspath; Diatomischer Kuphonspath, so v.w. Laumontit …   Pierer's Universal-Lexikon

  • Diatom — Diatom, bei Mohs Mineralien, die nach einer Richtung leicht theilbar sind, z.B. Schillerspath, der deßwegen vorzugsweise D. genannt wird …   Herders Conversations-Lexikon

  • diatom — 1845, coined from Gk. diatomos cut in two, from diatemnein to cut through, from dia through (see DIA (Cf. dia )) + temnein to cut (see TOME (Cf. tome)). So called because they typically appear to have been cut in half. Related: Diatomic …   Etymology dictionary

  • diatom — ► NOUN Biology ▪ a single celled alga which has a cell wall of silica. DERIVATIVES diatomaceous adjective. ORIGIN from Greek diatomos cut in two …   English terms dictionary

  • diatom — [dī′e täm΄, dī′ətəm] n. [ModL diatoma < Gr diatomos, cut in two < diatemnein, to cut through < dia , through + temnein, to cut: see TOMY] any of a class (Bacillariophyceae) of microscopic algae (division Chromophycota), one celled or in… …   English World dictionary

  • Diatom — For a molecule of two atoms, see Diatomic molecule. Diatoms Marine diatoms Scientific classification Domain …   Wikipedia

  • diatom — noun Etymology: ultimately from Greek diatomos cut in half, from diatemnein to cut through, from dia + temnein to cut more at tome Date: 1845 any of a class (Bacillariophyceae) of minute planktonic unicellular or colonial algae with silicified… …   New Collegiate Dictionary

  • Diatom — Bacillariophyta Bacillariophyta ou Diatomées …   Wikipédia en Français

  • diatom — Algae of the division Bacillariophyta; largely unicellular and characterized by having cell walls of hydrated silica embedded in an organic matrix. The cell walls are formed in two halves that fit together like the lid and base of a pillbox and… …   Dictionary of molecular biology


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