''Nautilus macromphalus'', the bellybutton nautilus, is a species of

nautilus The nautilus (, ) is a pelagic marine mollusc of the cephalopod family Nautilidae. The nautilus is the sole extant family of the superfamily Nautilaceae and of its smaller but near equal suborder, Nautilina. It comprises six living species ...

native to the waters off New Caledonia, the

Loyalty Islands The Loyalty Islands Province (French ''Province des îles Loyauté'') is one of three administrative subdivisions of New Caledonia encompassing the Loyalty Island (french: Îles Loyauté) archipelago in the Pacific, which are located northeast o ...

, and northeastern Australia. The shell of this species lacks a

callus A callus is an area of thickened and sometimes hardened skin that forms as a response to repeated friction, pressure, or other irritation. Since repeated contact is required, calluses are most often found on the feet and hands, but they may o ...

, leaving the

umbilicus Umbilicus may refer to: *The navel or belly button *Umbilicus (mollusc), a feature of gastropod, Nautilus and Ammonite shell anatomy * ''Umbilicus'' (plant), a genus of over ninety species of perennial flowering plants *Umbilicus urbis Romae The ...

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 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 neighbour Tiga Island, a ...

, the

. Based on these

radiocarbon date Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for Chronological dating, determining the age of an object containing organic material by using the properties of carbon-14, radiocarbon, a radioactive Isotope ...

s 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 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