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Branchial arch
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<h2 id="function">Function</h2> <p>The branchial system is typically used for respiration and/or feeding. Many fish have modified posterior gill arches into <a href="/facts/Pharyngeal_jaw/LnBMfdh1">pharyngeal jaws</a>, often equipped with specialized <a href="/facts/Pharyngeal_teeth/PhghwJy9">pharyngeal teeth</a> for handling particular prey items (long, sharp teeth in carnivorous moray eels compared to broad, crushing teeth in durophagous black carp). In amphibians and reptiles, the hyoid arch is modified for similar reasons. It is often used in <a href="/facts/Buccal_pumping/mNfT11AU">buccal pumping</a> and often plays a role in tongue protrusion for prey capture. In species with highly specialized <a href="/facts/Projectile_use_by_non-human_organisms/Rckt526K">ballistic tongue movements</a> such as <a href="/facts/Chameleon/rY7XCc30">chameleons</a> or some <a href="/facts/Plethodontidae/oJH5dWQm">plethodontid</a> <a href="/facts/Salamander/5pKurkwV">salamanders</a>, the hyoid system is highly modified for this purpose, while it is often hypertrophied in species which use <a href="/facts/Suction_feeding/Fow990hf">suction feeding</a>. Species such as snakes and monitor lizards, whose tongue has evolved into a purely sensory organ, often have very reduced hyoid systems. </p> <h2 id="components">Components</h2> <p>The primitive arrangement is 7 (possibly 8) arches, each consisting of the same series of paired (left and right) elements. order from dorsal-most (highest) to ventral-most (lowest), these elements are the pharyngobranchial, epibranchial, ceratobranchial, hypobranchial, and basibranchial. The pharyngobranchials may articulate with the <a href="/facts/Neurocranium/dzqkVdLQ">neurocranium</a>, while the left and right basibranchials connect to each other (often fusing into a single bone). When part of the hyoid arch, the names of the bones are altered by replacing "-branchial" with "-hyal", thus "ceratobranchial" becomes "ceratohyal".<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> </p> <ul><li>The Basihyals and Basibranchials lie at the midline of the lower edge of the throat. Almost all modern <a href="/facts/Chondrichthyes/xcW7PJDU">chondrichthyans</a> have a single midline basihyal, as do many <a href="/facts/Teleost/1YULPGW5">teleosts</a>, <a href="/facts/Lungfish/oNNrFFoE">lungfish</a>, and <a href="/facts/Tetrapodomorpha/rxUSNa98">tetrapodomorphs</a>. In <a href="/facts/Tetrapod/vWpAxzAW">tetrapods</a>, the basihyal is modified into a structure known as the <a href="/facts/Hyoid_bone/yAa2Vatb">hyoid bone</a>, which provides muscle attachment for the <a href="/facts/Tongue/oW4tp3a0">tongue</a>, <a href="/facts/Pharynx/51F3eVms">pharynx</a>, and <a href="/facts/Larynx/0bhtXI3Q">larynx</a>. Basibranchials, which are most common in <a href="/facts/Osteichthyes/nXoXEj3a">osteichthyans</a>, have the form of one or more rod-like bones projecting backwards along the midline of the throat.</li> <li>The Ceratohyals and Ceratobranchials lie above their respective basi- components, slanting backwards and upwards. They are often the largest bony components of the gill system, as well as the most essential and abundant components. Small connecting bones known as Hypophyals or Hypobranchials may link the basi- and cerato- components, and hypobranchials in particular are common among all types of fish. Paired hypophyals are characteristic of living osteichthyans. Living chondrichthyans lack hypohyals, though several extinct forms are known to have had them.</li> <li>The Epihyals and Epibranchials lie above their respective cerato- components, slanting forwards, upwards, and often inwards. Along with the ceratohyals and ceratobranchials, they are also essential components of the gill system, found in every fish. In filter-feeding fish, the epibranchials often host <a href="/facts/Gill_raker/aJIws2wV">gill rakers</a>, specialized spines projecting backwards to trap plankton. The epihyal is more commonly known as the <a href="/facts/Hyomandibula/9SV2HWxW">hyomandibula</a>, which is homologous to the sound-sensitive <a href="/facts/Stapes/TbLLQTrw">stapes</a> (sometimes known as the <a href="/facts/Columella_(auditory_system)/50o1Le4K">columnella</a>) of tetrapods.</li> <li>The Pharhyngobranchials are the most dorsal bony elements of the gill system, connecting to the upper extent of the epibranchials. Living chondrichthyans have large pharyngobranchials which lean backwards and upwards. Osteichthyans, on the other hand, have two different types of pharyngobranchials: Suprapharyngobranchials are toothless structures similar to those of chondrichthyans, while Infrapharyngobranchials often possess teeth and lean inwards and forwards, forming the roof of the throat. A hyoid equivalent of the pharyngobranchial, the Pharyngohyal, is only found in living <a href="/facts/Holocephali/9gFKBV35">holocephalans</a>, also known as <a href="/facts/Chimaera/gUmgE3Jl">chimaeras</a>.</li></ul> <h2 id="amniotes">Amniotes</h2> <p><a href="/facts/Amniotes/TeLtDTrJ">Amniotes</a> do not have <a href="/facts/Gills/FWgM3Jp8">gills</a>. The gill arches form as <a href="/facts/Pharyngeal_arch/12PBkJEN">pharyngeal arches</a> during <a href="/facts/Human_embryonic_development/JeVmIcT0">embryogenesis</a>, and lay the basis of essential structures such as <a href="/facts/Jaw/6a11Csjh">jaws</a>, the <a href="/facts/Thyroid_gland/bjovTJVu">thyroid gland</a>, the <a href="/facts/Larynx/0bhtXI3Q">larynx</a>, the <i>columella</i> (corresponding to the <a href="/facts/Stapes/TbLLQTrw">stapes</a> in <a href="/facts/Mammal/phSwTzBo">mammals</a>) and in mammals, the <a href="/facts/Ossicles/HocTMPqc">malleus and incus</a>.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> Studies on <a href="/facts/Placoderm/kknCSuQ7">placoderms</a> also show that the <a href="/facts/Shoulder_girdle/XyWsm4hv">shoulder girdle</a> also originated from gill arches.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> </p> <h2 id="external-links">External links</h2> <ul><li><a href="https://web.archive.org/web/20101220204210/http://palaeos.com/Vertebrates/Bones/Gill_Arches/Gill_Arches.html">The Gill Arches: Overview</a>, <i><a href="/facts/Palaeos/BDA8FEfv">Palaeos</a></i>. Retrieved 30 November 2014.</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Scott, Thomas (1996). Concise encyclopedia biology. Walter de Gruyter. p. 542. ISBN 978-3-11-010661-9. <a href="978-3-11-010661-9" target="_blank">978-3-11-010661-9</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Romer, A.S. (1949): The Vertebrate Body. W.B. Saunders, Philadelphia. (2nd ed. 1955; 3rd ed. 1962; 4th ed. 1970) <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Szarski, Henryk (1957). "The Origin of the Larva and Metamorphosis in Amphibia". The American Naturalist. 91 (860). Essex Institute: 287. doi:10.1086/281990. JSTOR 2458911. S2CID 85231736. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Clack, J. A. (2002): Gaining ground: the origin and evolution of tetrapods. Indiana University Press, Bloomington, Indiana. 369 pp <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Pradel, Alan; Maisey, John G.; Tafforeau, Paul; Mapes, Royal H.; Mallatt, Jon (16 April 2014). "A Palaeozoic shark with osteichthyan-like branchial arches". Nature. 509 (7502): 608–611. Bibcode:2014Natur.509..608P. doi:10.1038/nature13195. ISSN 1476-4687. PMID 24739974. S2CID 3504437. <a href="https://www.nature.com/articles/nature13195" target="_blank">https://www.nature.com/articles/nature13195</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Romer, A.S. (1949): The Vertebrate Body. W.B. Saunders, Philadelphia. (2nd ed. 1955; 3rd ed. 1962; 4th ed. 1970) <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Brazeau et al, Fossil evidence for a pharyngeal origin of the vertebrate pectoral girdle, Nature volume 623, pages550–554 (2023) <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> </ol>