The word pharynx (OED 2nd edition, 1989.Entry "pharynx" in Merriam-Webster Online Dictionary, retrieved 2012-07-28.) is derived from the Greek φάρυγξ phárynx, meaning "throat". Its plural form is pharynges or pharynxes , and its adjective form is pharyngeal ( or ).
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The planarians cover, or cap, the prostomium, peristomium, and anterior end to stop the violent reaction by the earthworm. To feed on their prey, species of Bipalium often evert their pharynges from their mouths, located on the midventral portion of their bodies, and secrete enzymes that begin the digestion of the prey. The liquefied tissues are sucked into the branching gut of the flatworms by ciliary action.
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Stilbonematines can be up to 10 mm long, with a club-like head. The worms are completely covered in a coat of ectosymbiotic sulfur-oxidizing bacteria except for the anterior region. The presence of the bacteria, which often contain intracellular inclusions of elemental sulfur, gives the worms a bright white appearance under incident light. They have small mouths and buccal cavities, and short pharynges.
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As they grow, they tend to move into deeper water. The tadpoles initially have three pairs of external gills and several rows of labial teeth. They pump water through their gills by movements of the floor of their mouths, trapping bacteria, single-celled algae, protozoans, pollen grains, and other small particles on mucus in a filtration organ in their pharynges. As they grow, they begin to ingest larger particles and use their teeth for rasping.
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Two families, the Eunicidae and Phyllodocidae, have evolved jaws, which can be used for seizing prey, biting off pieces of vegetation, or grasping dead and decaying matter. On the other hand, some predatory polychaetes have neither jaws nor eversible pharynges. Selective deposit feeders generally live in tubes on the sea-floor and use palps to find food particles in the sediment and then wipe them into their mouths. Filter feeders use "crowns" of palps covered in cilia that wash food particles towards their mouths.
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The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the esophagus and larynx – the tubes going down to the stomach and the lungs. It is found in vertebrates and invertebrates, though its structure varies across species. In humans, the pharynx is part of the digestive system and the conducting zone of the respiratory system. (The conducting zone—which also includes the nostrils of the nose, the larynx, trachea, bronchi, and bronchioles—filters, warms and moistens air and conducts it into the lungs).
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In 1997 he used the photolysis technique to study Caenorhabditis elegans. (commonly known as the roundworm). He used the technique to determine which neurotransmitters were being secreted by the intricate network of neurons in the worms’ pharynges and determine the neurotransmitters’ target cells. Hess summarized his methods and findings in the publication: “Identification of Chemical Synapses in the Pharynx: Caenorhabditis elegans.” In his article “How Fast Does the γ-Aminobutyric Acid Receptor Channel Open? Kinetic Investigations in the Microsecond Time Region Using a Laser-Pulse Photolysis Technique” published in 1999, Hess explores the GABAA receptor and its kinetics.
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However, the septa are often incomplete in annelids that are semi-sessile or that do not move by peristalsis or by movements of parapodia – for example some move by whipping movements of the body, some small marine species move by means of cilia (fine muscle-powered hairs) and some burrowers turn their pharynges (throats) inside out to penetrate the sea-floor and drag themselves into it. The fluid in the coelomata contains coelomocyte cells that defend the animals against parasites and infections. In some species coelomocytes may also contain a respiratory pigment – red hemoglobin in some species, green chlorocruorin in others (dissolved in the plasma) – and provide oxygen transport within their segments. Respiratory pigment is also dissolved in the blood plasma.
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Species of Sphaerosyllis, however, always exhibit papillae on the pharyngeal opening, their pharyngeal tooth is conical and is always located on or very near to the anterior margin of the pharynx. They usually count with a short proventricle, itself provided with large muscle cell rows, large posterior acicula (which is distally bent at 90°), blades of compound chaetae which are short and unidentate, and offspring developing ventrally, females without capillary notochaetae, only present on males. Sphaerosyllis horrockensis, Sphaerosyllis belizensis, and Sphaerosyllis centroamericana were transferred to Erinaceusyllis under these distinguishing characteristics. At the same time, Prosphaerosyllis is close to Erinaceusyllis, but its species' pharyngeal teeth are rhomboidal to oval and located near the middle of their pharynges; also their antennae are short, tentacular and their dorsal cirri have a bulbous cirrophore and retractile cirrostyle.
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The septa of such species also enable them to change the shapes of individual segments, which facilitates movement by peristalsis ("ripples" that pass along the body) or by undulations that improve the effectiveness of the parapodia. In species with incomplete septa or none, the blood circulates through the main body cavity without any kind of pump, and there is a wide range of locomotory techniques – according to Rout Radhamohan some burrowing species turn their pharynges inside out to drag themselves through the sediment. Earthworms are oligochaetes that support terrestrial food chains both as prey and in some regions are important in aeration and enriching of soil. The burrowing of marine polychaetes, which may constitute up to a third of all species in near-shore environments, encourages the development of ecosystems by enabling water and oxygen to penetrate the sea floor.
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