''Nautilus macromphalus'', the bellybutton nautilus, is a species of nautilus native to the waters off

New Caledonia ) , anthem = "" , image_map = New Caledonia on the globe (small islands magnified) (Polynesia centered).svg , map_alt = Location of New Caledonia , map_caption = Location of New Caledonia , mapsize = 290px , subdivision_type = Sovereign st ...

, the Loyalty Islands, and northeastern

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

. 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

tentacle In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work main ...

s 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 A cenote ( or ; ) is a natural pit, or sinkhole, resulting from the collapse of limestone bedrock that exposes groundwater. The regional term is specifically associated with the Yucatán Peninsula of Mexico, where cenotes were commonly used for ...

Lifou Lifou is a communes of France, commune of France in the Loyalty Islands Province of New Caledonia in the Pacific Ocean. Geography Lifou is made up of Lifou Island, the largest and most heavily populated of the Loyalty Islands, its smaller neig ...

, 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 Karst is a topography formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. It has also been documented for more weathering-resistant ro ...

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 The Gazelle Peninsula is a large peninsula in northeastern East New Britain, Papua New Guinea located on the island of New Britain within the Bismarck Archipelago, situated in the southwestern Pacific Ocean. The Rabaul caldera is located on the ...

, where Arthur Willey attempted to catch ''N. macromphalus''

References

* Norman, M. 2000. ''Cephalopods: A World Guide''. Hackenheim, ConchBooks, p. 30.

External links

{{Taxonbar, from=Q940450 Nautiluses Cephalopods of Australia Molluscs described in 1848