nematocyst

nematocyst
—nematocystic, adj.
/nem"euh teuh sist', ni mat"euh-/, n. Zool.
an organ in coelenterates consisting of a minute capsule containing an ejectable thread that causes a sting.
[1870-75; NEMATO- + -CYST]

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      minute, elongated, or spherical capsule produced exclusively by members of the phylum Cnidaria (e.g., jellyfish, corals, sea anemones). Several such capsules occur on the body surface. Each is produced by a special cell called a cnidoblast and contains a coiled, hollow, usually barbed thread, which quickly turns outward (i.e., is everted) from the capsule upon proper stimulation. The purpose of the thread, which often contains poison, is to ward off enemies or to capture prey.

      When stimulated by chemical or mechanical cues, a lidlike structure on the top of the capsule pops aside, and the thread everts explosively with a twisting motion. As eversion and twisting proceed, the barbs act like a drill, penetrating into (and pulling the thread into) the foreign object. If a toxin is present, it passes through the hollow thread, penetrating and paralyzing the victim's tissues. After eversion, the thread separates from the nematocyst. The threads of some nematocysts ensnare small prey by wrapping about them. The stinging effect of nematocysts in the Portuguese man-of-war and some jellyfish (qq.v.) species can be extremely painful to humans and may cause paralysis, shock, and even death.

      Nematocysts are a type of cnidae, and it is the presence of cnidae that separates jellyfish and other cnidarians from other animals. Cnidae are among the most complex intracellular secretion products known.

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Universalium. 2010.

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Look at other dictionaries:

  • Nematocyst — Nem a*to*cyst, n. [Nemato + cyst.] (Zo[ o]l.) A lasso cell, or thread cell. See {Lasso cell}, under {Lasso}. [1913 Webster] …   The Collaborative International Dictionary of English

  • nematocyst — (n.) 1875, from nemato , comb. form of Gk. nema, nematos thread (gen. nematos), from stem of nein to spin (see NEEDLE (Cf. needle) (n.)) + CYST (Cf. cyst) …   Etymology dictionary

  • nematocyst — [nem′ə tō sist΄] n. [ NEMATO + CYST] any of the intracellular stinging structures characteristic of all cnidarians, as the jellyfish: it contains a threadlike sting nematocystic adj …   English World dictionary

  • nematocyst — (= cnidocyst) Stinging mechanism used for defence and prey capture by Hydra and other members of the Cnidaria (Coelenterata). It is located within a specialized cell, the nematocyte and consists of a capsule containing a coiled tube. When the… …   Dictionary of molecular biology

  • nematocyst — noun Etymology: International Scientific Vocabulary Date: 1875 one of the stinging organelles of coelenterates used in catching prey …   New Collegiate Dictionary

  • nematocyst — См. cnida …   Dictionary of invertebrate zoology

  • nematocyst — noun A capsule, in certain cnidarians, containing a barbed, threadlike tube that delivers a paralyzing sting Syn: cnidocyte …   Wiktionary

  • nematocyst — A stinging cell of coelenterates consisting of a poison sac and a coiled barbed sting capable of being ejected and penetrating the skin of an animal on contact; of considerable consequence in large jellyfish and in the Portuguese man of war whose …   Medical dictionary

  • nematocyst — nemÉ™tÉ™sɪst ,nɪ mæt n. organ in coelenterates that contains a long very thin stinging appendage, lasso cell …   English contemporary dictionary

  • nematocyst — [nɪ matə(ʊ)sɪst, nɛmət ] noun Zoology a specialized cell in the tentacles of a jellyfish or other coelenterate, containing a barbed or venomous coiled thread that can be projected in self defence or to capture prey …   English new terms dictionary

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