Nomarski micrograph of a Ruthenium-red stained nematocyst from Aiptasia pallida, the pale anemone. The red dye stains the polyanionic venom proteins found inside the capsule of this partially discharged nematocyst.

A cnidocyte, cnidoblast or nematocyte, is a type of venomous cell unique to the phylum Cnidaria (corals, sea anemones, hydrae, jellyfish, etc.). It evolved in these aquatic animals as a means for them to catch prey and defend themselves from predators, despite being morphologically simple, lacking a skeleton and usually being sessile; they prey on fish and crustaceans. A cnidocyte fires a structure that contains the toxin, from a characteristic sub-cellular organelle called a cnidocyst (or cnida or nematocyst). This is, for instance, responsible for the stings delivered by jellyfish. Image File history File links Size of this preview: 800 × 535 pixelsFull resolution (1347 × 900 pixel, file size: 689 KB, MIME type: image/jpeg)Nomarski micrograph of a Ruthenium-red stained nematocyst from Aiptasia pallida, the pale anemone. ... Image File history File links Size of this preview: 800 × 535 pixelsFull resolution (1347 × 900 pixel, file size: 689 KB, MIME type: image/jpeg)Nomarski micrograph of a Ruthenium-red stained nematocyst from Aiptasia pallida, the pale anemone. ... A micrograph is a photograph or similar image taken through a microscope or similar device to show a magnified image of an item. ... Wasp sting, with droplet of venom Venom (literally, poison of animal origin) is any of a variety of toxins used by animals, for the purpose of defense and hunting. ... Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the... In biological taxonomy, a phylum (Greek plural: phyla) is a taxon in the rank below kingdom and above class. ... Subphylum/Classes[1] Anthozoa — corals and sea anemones Medusozoa:[2] Cubozoa — sea wasps or box jellyfish Hydrozoa — hydroids, hydra-like animals Polypodiozoa Scyphozoa — jellyfish Staurozoa — stalked jellyfish unranked: Myxozoa - parasites Cnidaria[3] (IPA: [4]) is a phylum containing some 11,000 species of apparently simple animals found exclusively in aquatic... Extant Subclasses and Orders Alcyonaria    Alcyonacea    Helioporacea Zoantharia    Antipatharia    Corallimorpharia    Scleractinia    Zoanthidea [1][2]  See Anthozoa for details For other uses, see Coral (disambiguation). ... Families Many, see text. ... Baron Strucker, retconned founder of HYDRA, wearing the HYDRA logo on his chest. ... Bold text For other uses, see Jellyfish (disambiguation). ... Look up sessile in Wiktionary, the free dictionary. ... For other uses, see Fish (disambiguation). ... For the Dutch band, see Crustacean (band). ... Schematic of typical animal cell, showing subcellular components. ...

Structure and action

A discharged nematocyst seen under a scanning electron microscope.

Each cnidocute cell contains an organelle called a cnidocyst, which comprises a bulb-shape capsule containing a coiled hollow thread-like structure attached to it. The externally-oriented side of the cell also has a hair-like trigger called a cnidocil. When the trigger is activated, the shaft of the cnidocyst penetrates the target organism, and the hollow thread is everted into it. This discharge is one of the fastest biological processes, takes no more than a few microseconds, and reaches accelerations of about 40,000g^[1]. After penetration, the toxic content of the nematocyst is injected into the target organism. The rapid activity of the injected neurotoxins immediately paralyzes the mobile prey, thus allowing the sessile cnidarian to devour it. Image File history File links Nematocyst-discharged. ... Image File history File links Nematocyst-discharged. ... SEM Cambridge S150 at Geological Institute, University Kiel, 1980 SEM opened sample chamber The scanning electron microscope (SEM) is a type of electron microscope capable of producing high-resolution images of a sample surface. ... To help compare orders of magnitude of different times this page lists times between 10−6 seconds and 10−5 seconds (1. ... Acceleration is the time rate of change of velocity and/or direction, and at any point on a velocity-time graph, it is given by the slope of the tangent to the curve at that point. ... The term g force or gee force refers to the symbol g, the force of acceleration due to gravity at the earths surface. ...

Means of discharge

The nematocyst capsule stores a large concentration of calcium ions, which are released from the capsule into the cytoplasm of the cnidocyte when the trigger is activated. This causes a large concentration gradient of calcium across the cnidocyte plasma membrane. The resulting osmotic pressure causes a rapid influx of water into the cell. This increase in water volume in the cytoplasm forces the coiled nematocyst to eject rapidly. For other uses, see Calcium (disambiguation). ... This article is about the electrically charged particle. ... Organelles. ... This article or section does not adequately cite its references or sources. ...

Prey detection

A nematocyte is able under some conditions to fire independently, but this presents several problems for the cnidarian. First, it must avoid stinging itself. Second, it must replace cnidocytes after discharge, as they are "single use" cells, and this costs a lot of energy. In order to regulate discharge, cnidocytes are connected as "batteries", containing several types of nematocytes connected to supporting cells and neurons. The supporting cells contain chemoreceptors, which, together with the mechanoreceptor on the cnidocyte (cnidocil), allow only the right combination of stimuli to cause discharge, such as prey swimming, and chemicals found in prey cuticle or skin. A Chemosensor, also known as chemoreceptor, is a cell or group of cells that transduce a chemical signal into an action potential. ... A mechanoreceptor is a sensory receptor that responds to mechanical pressure or distortion. ... Eponychium is the anatomical term for the human cuticle In biology, the term cuticle or cuticula is given to to a variety of tough but flexible, non-mineral outer coverings of an organism, or part of an organism, that provide prtoection. ...

Types of nematocysts

Over 30 types of nematocytes are found in different cnidarians. They can be divided into the following groups:

1. Penetrant: A harpoon-like structure used to penetrate
2. Glutinant: Sticky surfaces used to stick to prey
3. Volvent: A lasso-like string that is fired at prey and wraps around a cellular projection on the prey
4. Ptychocyst: A special type of nematocyte found on burrowing (tube) anemones, which help create the tube in which the animal lives.

Depending on the species, one or several types can appear simultaneously on the organism.

Nematocyst toxicity

Nematocysts are very efficient weapons. A single nematocyst has been shown to suffice to paralyze a small arthropod (Drosophila larva). The most deadly cnidocytes (to humans, at least) are found on the body of a box jellyfish. One member of this family, the Sea Wasp, Chironex fleckeri, is "claimed to be the most venomous marine animal known," according to the Australian Institute of Marine Science. It causes excruciating pain to humans, often followed by death, sometimes within two or three minutes. The chance of survival if stung while swimming alone is "virtually zero." Other cnidarians, such as the jellyfish Cyanea capillata (the "The Adventure of the Lion's Mane" made famous by Sherlock Holmes) or the hydrozoan Physalia physalis (Portuguese Man o' War, "Bluebottle") can cause extremely painful and sometimes fatal stings. On the other side, Aggregating sea anemones may have the lowest sting intensity, perhaps due to nematocysts not penetrating the skin, providing only a feeling of that similar to touching sticky candies to human fingers. Besides feeding and defense, sea anemone colonies use cnidocytes to sting one another in order to win space. Subphyla and Classes Subphylum Trilobitomorpha Trilobita - trilobites (extinct) Subphylum Chelicerata Arachnida - spiders,scorpions, etc. ... Type species Drosophila funebris (Fabricius, 1787) Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called fruit flies, or more appropriately vinegar flies, wine flies, pomace flies, grape flies, and picked fruit-flies, a reference to the characteristic of many species to linger... A larval insect A larva (Latin; plural larvae) is a juvenile form of animal with indirect development, undergoing metamorphosis (for example, insects or amphibians). ... Families see text Jellyfish net enclosure at Ellis Beach, Queensland Box jellyfish are water-dwelling invertebrates belonging to the class Cubozoa, named for their cube-shaped medusae. ... Binomial name Southcott, 1956 Chironex fleckeri, commonly known as box jellyfish, marine stinger and formerly the sea wasp, is a highly venomous species of box jellyfish. ... The Australian Institute of Marine Science (AIMS) is a state-of-the-art marine research centre located primarily at Cape Ferguson, 50km south of Townsville in North Queensland, Australia. ... Binomial name Cyanea capillata (Linnaeus, 1758) The Lions mane jellyfish (Cyanea capillata) is the largest known species of jellyfish. ... The Adventure of the Lions Mane, one of the 56 Sherlock Holmes short stories written by British author Sir Arthur Conan Doyle, is one of 12 stories in the cycle collected as The Case Book of Sherlock Holmes. ... A portrait of Sherlock Holmes by Sidney Paget from the Strand Magazine, 1891 Sherlock Holmes is a fictional detective of the late 19th and early 20th centuries, who first appeared in publication in 1887. ... Binomial name (Linnaeus, 1758) The Portuguese Man O War (Physalia physalis), also known as the bluebubble or bluebottle, is commonly thought of as a jellyfish but is actually a siphonophore—a colony of specialised polyps and medusoids. ... This article is about swarms in biology. ...

But venom from animals such as cnidarians, scorpions, and spiders may be species-specific: a substance that is weakly toxic for humans or other mammals, but very toxic to the natural prey or predators of the venomous animal. Such specificity has been used to create new medicines and bioinsecticides. For other uses, see Toxin (disambiguation). ... For other uses, see Scorpion (disambiguation). ... Diversity 111 families, 40,000 species Suborders Mesothelae Mygalomorphae Araneomorphae  See table of families Wikispecies has information related to: Spiders Spiders are predatory invertebrate animals that have two body segments, eight legs, no chewing mouth parts and no wings. ...

Animals in the phylum Ctenophora ("sea-gooseberries" or "comb jellies") are transparent and jelly-like but have no nematocysts, and are harmless to humans. Phylum (plural: phyla) is a taxon used in the classification of animals, adopted from the Greek phylai the clan-based voting groups in Greek city-states. ... Classes Tentaculata Nuda Ctenophores are jellyfish-like animals commonly called comb jellies, sea gooseberries, sea walnuts, or Venus girdles. ...

References

1. ^ G. Kass-Simon and A.A. Scappaticci, Jr. The behavioral and developmental physiology of nematocysts. Can. J. Zool. Vol. 80, 2002, pp 1772-1794

External links

• Dangerous marine animals of Northern Australia: the Sea Wasp Australian Institute of Marine Science; dangers of box jellyfish
• Nematocysts Firing Movie