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

nautilus A nautilus (; ) is any of the various species within the cephalopod family Nautilidae. This is the sole extant family of the superfamily Nautilaceae and the suborder Nautilina. It comprises nine living species in two genera, the type genus, ty ...

native to the waters off

New Caledonia New Caledonia ( ; ) is a group of islands in the southwest Pacific Ocean, southwest of Vanuatu and east of Australia. Located from Metropolitan France, it forms a Overseas France#Sui generis collectivity, ''sui generis'' collectivity of t ...

and northeastern

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

. The shell of this species lacks a

callus A callus (: calluses) 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, b ...

, 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 when a collapse of limestone bedrock exposes groundwater. The term originated on the Yucatán Peninsula of Mexico, where the ancient Maya commonly used cenotes for water supplies, and ...

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

, the

Loyalty Islands Loyalty Islands Province (, ) is one of the three top-level administrative subdivisions of New Caledonia. It encompasses the Loyalty Islands () archipelago in the Pacific Ocean, located northeast of the New Caledonian mainland of Grande Terre. ...

. Based on these

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

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 Karst () is a topography formed from the dissolution of soluble carbonate rocks such as limestone and Dolomite (rock), dolomite. It is characterized by features like poljes above and drainage systems with sinkholes and caves underground. Ther ...

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 t ...

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

References

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

External links

{{Authority control Nautiluses Cephalopods of Australia Cephalopods described in 1848 Fauna of the Central Indo-Pacific