desmid

desmid
desmidian, adj.
/dez"mid/, n.
any single-celled freshwater algae of the family Desmidiaceae, characterized by a division of the body into mirror-image halves joined by a bridge containing the nucleus, and having a spiny or bristly exterior: sometimes forming into colonies or branching filaments.
[1860-65; < NL Desmidium a genus of the family < Gk desm(ós) a band, chain (cf. deîn to fasten) + NL -idium -IDIUM]

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Any of a group of one-celled, microscopic green algae characterized by great variation in cell shape.

Typically the cell is divided symmetrically into semicells connected at a central point. Desmids are found worldwide, usually in acid bogs or lakes. Since most species have a limited range, the presence of specific desmids is helpful in characterizing water samples.

Desmid (Micrasterias), highly magnified

Winton Patnode
Photo Researchers

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      any of the beautiful, single-celled (sometimes filamentous or colonial), microscopic green algae of the order Zygnematales, class Charophyceae, characterized by extensive variation in cell shape. Typically the cell is divided symmetrically into semicells connected at a central isthmus. The three-layered cell wall is impregnated with openings or pores and pectin spicules; irregular desmid movement is caused by the flow of a gelatinous substance through these pores. Conjugation (temporary union for the exchange of nuclear material) is the usual method of sexual generation. In some species a conjugation tube is formed. In others the two conjugant protoplasts unite in a gelatinous sheath that surrounds the cells. Usually cell division occurs in the region of the isthmus, each half develops another semicell, and in due course two complete desmids are formed. Spores are rare. The distribution of desmids is worldwide, usually in acid bogs or lakes. Since most species have a limited ecological range, the presence of specific desmids is helpful in characterizing water samples. One of the more common desmid genera, the sickle-shaped Closterium, often contains gypsum crystals in cell vacuoles.

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Universalium. 2010.

См. также в других словарях:

  • Desmid — Des mid, Desmidian Des*mid i*an, n. [Gr. desmo s chain + e i^dos form.] (Bot.) A microscopic plant of the family {Desmidi[ae]}, a group of unicellular alg[ae] in which the species have a greenish color, and the cells generally appear as if they… …   The Collaborative International Dictionary of English

  • desmid — [des′mid] n. [ModL desmidium, dim. < Gr desmos, a chain; akin to dein, to bind: see DIADEM] any of a group of microscopic, freshwater green algae having single cells composed of two identical half cells with the nucleus located between them …   English World dictionary

  • desmid — noun Etymology: ultimately from Greek desmos Date: 1862 any of numerous unicellular or colonial green algae (order Zygnematales, especially family Desmidiaceae) …   New Collegiate Dictionary

  • Desmid — Taxobox name = Desmids image width = 300px image caption = regnum = Plantae divisio = Charophyta classis = Zygnemophyceae ordo = Desmidiales subdivision ranks = Families subdivision = Closteriaceae Desmidiaceae Gonatozygaceae PeniaceaeDesmids are …   Wikipedia

  • desmid — Chlorophyte algae that are usually freshwater living and unicellular. Their cell wall often has elaborate ornamented shape …   Dictionary of molecular biology

  • desmid — noun /ˈdɛz.mɪd/ Any of about 5000 species of mostly unicellular freshwater green algae belonging to the order Desmidiales. Desmids, which are exclusively freshwater algae, are so named because the first of these green microorganisms to be… …   Wiktionary

  • desmid — des·mid (desґmid) unicellular, free floating, aquatic algae characterized by symmetrical, curved, spiny or lacey bodies with a median constriction dividing the cell into two equal halves …   Medical dictionary

  • desmid — [ dɛzmɪd] noun Biology a single celled freshwater alga which appears to be composed of two rigid cells with a shared nucleus. [Family Desmidiaceae.] Origin C19: from mod. L. Desmidium (genus name), from Gk desmos band, chain (because the algae… …   English new terms dictionary

  • desmid — des·mid …   English syllables

  • desmid — des•mid [[t]ˈdɛz mɪd[/t]] n. mcr any green algae of the family Desmidiaceae, each alga being composed of symmetrical half cells bridged by a nucleus and usu. living colonially in a branching mat • Etymology: 1860–65; < NL Desmidium a genus… …   From formal English to slang


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