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An otolith (οτο-, ''oto-'', ear + λιθος, ''lithos'', a stone), also called statoconium or otoconium, is a structure in the saccule or utricle of the inner ear, specifically in the vestibular labyrinth of vertebrates. They have been identified in both extinct and extant vertebrates.〔Sahney, S. and M.V.H. Wilson 2001. Extrinsic labyrinth infillings imply open endolymphatic ducts in Lower Devonian osteostracans, acanthodians, and putative chondrichthyans. Journal of Vertebrate Paleontology 21:660-669.〕 The saccule and utricle, in turn, together make the ''otolith organs''. They are sensitive to gravity and linear acceleration. Because of their orientation in the head, the utricle is sensitive to a change in horizontal movement, and the saccule gives information about vertical acceleration (such as when in an elevator). ==Description== Endolymphatic infillings such as otoliths or statoconia are structures in the saccule and utricle of the inner ear, specifically in the vestibular labyrinth of all vertebrates (fish, amphibians, reptiles, mammals and birds). In vertebrates, the saccule and utricle together make the ''otolith organs''. Both statoconia and otoliths are used as gravity, balance, movement, and directional indicators in all vertebrates and have a secondary function in sound detection in higher aquatic and terrestrial vertebrates. They are sensitive to gravity and linear acceleration. Because of their orientation in the head, the utricle is sensitive to a change in horizontal movement, and the saccule gives information about vertical acceleration (such as when in an elevator). Statoliths can be found in many invertebrate groups but are not contained in the structure of an inner ear. Mollusk statoliths are of a similar morphology to the displacement-sensitive organs of vertebrates;〔Gauldie, R. W. 1993. Polymorphic structure of fish otoliths. Journal of Morphology 218:1–28.〕 however, the function of the mollusk statocyst is restricted to gravity detection and possibly some detection of angular momentum.〔Wolff, H. C. 1973. Multi-directional sensitivity of statocyst receptor cells of the opisthobranch gastropod Aplysia limacina. Marine Behavior and Physiology 1:361–373.〕 These are analogous structures, with similar form and function but not descended from a common structure. Statoconia (also called otoconia) are numerous grains, often spherical in shape, between 1 and 50 µm; collectively. Statoconia are also sometimes termed a statocyst. Otoliths (also called statoliths) are agglutinated crystals or crystals precipitated around a nucleus, with well defined morphology and together all may be termed endolymphatic infillings.〔Sahney, S. and M.V.H. Wilson 2001. Extrinsic labyrinth infillings imply open endolymphatic ducts in Lower Devonian osteostracans, acanthodians, and putative chondrichthyans. Journal of Vertebrate Paleontology 21:660-669.〕〔Nolf, D. 1985. Otolithi Piscium; in H.-P. Schultze (ed.), Handbook of Paleoichthyology, Vol. 10. Gustav Fischer Verlag, Stuttgart, 145pp.〕〔Schultze, H.-P. 1990. A new acanthodian from the Pennsylvanian of Utah, U.S.A. and the distribution of otoliths in gnathostomes. Journal of Vertebrate Paleontology 10:49–58.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「otolith」の詳細全文を読む スポンサード リンク
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