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| name = ''Spirula spirula'' | status = LC | status_system = IUCN3.1 |status_ref =〔Barratt, I. & Allcock, L. (2012). (''Spirula spirula'' ). The IUCN Red List of Threatened Species. Version 2014.2.〕 | image = Spirula spirula1.jpg | image_caption = Dorsal view of female | image2 = Spirula spirula2.jpg | image2_caption = Ventral view of female (chromatophores of mantle missing) | regnum = Animalia | phylum = Mollusca | classis = Cephalopoda | subclassis = Coleoidea | superordo = Decapodiformes | ordo = Spirulida | subordo = Spirulina | familia = Spirulidae | familia_authority = Owen, 1836 | genus = ''Spirula'' | genus_authority = Lamarck, 1799 | species = ''S. spirula'' | binomial = ''Spirula spirula'' | binomial_authority = (Linnaeus, 1758) | synonyms = *''Nautilus spirula'' Linnaeus, 1758 }} ''Spirula spirula'' is a species of deep-water squid-like cephalopod mollusk. It is the only extant member of the genus ''Spirula'', the family Spirulidae, and the order Spirulida. Because of the shape of its internal shell, it is commonly known as the ram's horn squid〔Norman, M. 2000. ''Cephalopods: A World Guide''. Hackenheim, ConchBooks.〕 or the little post horn squid. Because the live animal has a light-emitting organ, it is also sometimes known as the tail-light squid. Live specimens of this cephalopod are very rarely seen, because it is a deep-ocean dweller. The small internal shell of the species is however quite a familiar object to many beachcombers. The shell of ''Spirula'' is extremely light in weight, very buoyant, and surprisingly durable; it very commonly floats ashore onto tropical beaches (and sometimes even temperate beaches) all over the world. This seashell is known to shell collectors as the ram's horn shell or simply as ''Spirula''. == Description == ''S. spirula'' has a squid-like body between 35 mm and 45 mm long. It is a decapod, with eight arms and two longer tentacles, all with suckers. The arms and tentacles can all be withdrawn completely into the mantle. The species lacks a radula (or, at most, has a vestigial radula).〔 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「Spirula」の詳細全文を読む スポンサード リンク
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