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''Acanthonautilus'' is an extinct genus in the nautilid family Solenochildae (Aipocerataceae) from the Upper Mississippian of North America and equivalent (uL Carb) strata in Europe, first described by Foord in 1896. ''Acanthonautilus'', like ''Solenochilus'', has an involute, globular shell of few volutions that enlargens with fair rapidity, with prominent lateral spines extending from the umbilical area at maturity. The siphuncle in ''Acanthonautilus'' is narrower than in ''Solenochilu''s and not as sinuous. As with ''Solenochilus'', septal necks on the outer, or ventral, side are straight, but those on the inner, or dosal, side rather than being recumbent are simply curved, cytochoanitic. Most of the siphuncle is thin connecting ring which from the outside is slightly ventrally concave and slightly dorsally convex between septa. ''Acanthonautilus'' may have been derived from ''Aipoceras'', or possibly ''Asymptoceras'' and give rise, principally through modification of the siphuncle, to ''Solenochilus''. ==''References''== * Kummel 1964; Nautiloidea-Nautilida, Treatise on Invertebrate Paleontology, Part K Nautiliodea, Geological Society of America and University of Kansas press. * Sepkoski, J.J. Jr. 2002. A compendium of fossil marine animal genera. D.J. Jablonski & M.L. Foote (eds.). ''Bulletins of American Paleontology'' 363: 1–560. (Sepkoski's Online Genus Database (CEPHALOPODA) ) ''See'' List of nautiloids 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「Acanthonautilus」の詳細全文を読む スポンサード リンク
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