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The chambered nautilus (Nautilus pompilius), also called the pearly nautilus, is the best-known species of nautilus. The shell, when cut away, reveals a lining of lustrous nacre and displays a nearly perfect equiangular spiral , although it is not a golden spiral .
Their structure lacks the gas-filled chambers present in chambered nautilus shells and is not a true cephalopod shell, but rather an evolutionary innovation unique to the genus. [1] It is used as a brood chamber, and to trap surface air to maintain buoyancy .
Though it more specifically refers to the species Nautilus pompilius, the name chambered nautilus is also used for any of the Nautilidae. All are protected under CITES Appendix II. [4] Depending on species, adult shell diameter is between 10 and 25 cm (4 and 10 inches).
A cross-section of a Nautilus pompilius shell, showing the large body chamber, shrinking camerae, concave septa, and septal necks (partial siphuncle supports) All nautiloids have a large external shell, divided into a narrowing chambered region (the phragmocone) and a broad, open body chamber occupied by the animal in life. The outer wall of ...
Nautilus have been noted to exhibit an extensive range of depth, close to 500 metres, however, they were demonstrated to be at risk of implosion when exceeding their depth and pressure limits. Depending on the species, the shells of live Nautilus will collapse at depths of 750 metres or deeper. [18] [4]
Allonautilus perforatus, also known as the Bali chambered nautilus, is a species of nautilus native to the waters around Bali, Indonesia. It is known only from drifted shells and, as such, is the least studied of the six recognized nautilus species. Thus, not much is known about it outside of the shell.