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''Nautilus macromphalus'', the bellybutton nautilus, is a species of nautilus native to the waters off New Caledonia, the Loyalty Islands, and northeastern Australia. The shell of this species lacks a callus, leaving the umbilicus exposed, in which the inner coils of the shell are visible. This opening constitutes about 15% of the shell diameter at its widest point. Like all ''Nautilus'' species, ''N. macromphalus'' usually lives at depths of several hundred metres. During the night, however, they rise to much shallower waters (2 to 20 m depth) to feed. The tentacles of this species are long and thin, having raised ridges which help provide grip when catching prey. ''N. macromphalus'' is the smallest species of nautilus. The shell is usually up to around 16 cm in diameter, although the largest specimen ever recorded measured 180 mm. More than 35 shells of ''N. macromphalus'' dating to around 6400–7100 years BP were found in a cenote on Lifou, the Loyalty Islands. Based on these radiocarbon dates it is thought the cenote was connected to marine waters for some 700 years before becoming cut off completely. During this time nautiluses were able to enter it through a flooded karst system. Many of these animals apparently became trapped and died there.〔(The ''Nautilus'' death cenote ). 2013 GSA Annual Meeting in Denver: 125th Anniversary of GSA (27-30 October 2013).〕 Image:nautilus_macromphalus_1.jpg|''N. macromphalus'' seen during a night dive in Sandal Wood Bay, Lifou, New Caledonia at a depth of 15 m Image:Nautilus_macromphalus_couple.jpg|Pair of ''N. macromphalus'' in Sandal Wood Bay Image:Nautilus macromphalus.png|''Nautilus macromphalus'' shell Image:Nautilus macromphalus anatomy.jpg|Anatomy of ''N. macromphalus'' from Arthur Willey's monograph, 1912 Image:Gazelle Peninsula.jpg|Map of Gazelle Peninsula, where Arthur Willey attempted to catch ''N. macromphalus'' ==References== * Norman, M. 2000. ''Cephalopods: A World Guide''. Hackenheim, ConchBooks, p. 30. 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「Nautilus macromphalus」の詳細全文を読む スポンサード リンク
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