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''Neopilina'' is a highly derived genus of modern monoplacophoran.〔Organisms, Genes and Evolution: Evolutionary Theory at the Crossroads ; Proceedings of the 7th International Senckenberg Conference By Dieter Stefan Peters, Michael Weingarten Contributor Dieter Stefan Peters Published by Franz Steiner Verlag, 2000 ISBN 3-515-07659-X, 9783515076593 243 pages〕 Some molecular results show that they fall within the polyplacophoran clade, although these results have been called into question. Fossil and morphological data show that they are rather derived and bear very little resemblance to an 'ancestral mollusc'.〔 == Anatomy == Its anatomy led researchers to believe that the cephalopods evolved from the Monoplacophora.〔 Its pair of preoral tentacles are considered homologous to those of gastropods; like prosobranch gastropod tentacles, their nerves connect to the cerebral ganglia.〔 The post-oral tentacles are equated with bivalves' labial flaps, cephalopods' arms, and scaphopods' captacula.〔 Cuticular hardenings around the mouth of the organism are considered to be jaw-like and very not far removed from the beaks of cephalopods or the jaws of many gastropods.〔 The presence of a single shell prompts comparisons to the cephalopod ''Nautilus'', but besides its bilateral symmetry and direction of coiling, there is not a clear equivalence; ''Nautilus shell is notably different in the possession of septa (and thus a siphuncle).〔 It bears a similar degree of similarity to most other mollusc groups, leading to speculation that it may reflect a relatively unchanged ancestral mollusc.〔 The shell itself is aragonitic, consisting mainly of a prismatic layer,〔 - contains spectacular SEM of prismatic nature of aragonite shell.〕 lined with nacre.〔 The organism bears five pairs of ctenidia (gills), unusually for molluscs; the rear two are homologous to the two pairs in ''Nautilus''. This is unlike the polyplacophora, who have a number of pairs of ctenidia, but this number varies and is not related to the number of their body 'segments'.〔 The foot and pallial groove are very difficult indeed to discriminate from the polyplacophora,〔 supporting its placement in this group by molecular methods〔 Its radula is not unlike that of the polyplacophora; notably, its fifth tooth is modified to be comb-like. 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「Neopilina」の詳細全文を読む スポンサード リンク
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