Temporal range: Early Pleistocene to Recent
The chambered nautilus, Nautilus pompilius, 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. The shell exhibits countershading, being light on the bottom and dark on top. This is to help avoid predators, because when seen from above, it blends in with the darkness of the sea, and when seen from below, it blends in with the light coming from above.
The chambered nautilus has more primitive eyes than some other cephalopods; the eye has no lens and thus is comparable to a pinhole camera. The species has about 90 tentacles with no suckers, which is also different from other cephalopods. Chambered nautiluses have a pair of rhinophores, which detect chemicals, and use olfaction and chemotaxis to find their food.[not verified in body]
Recently, scientists have become alarmed at declining populations of nautilus resulting from overfishing, and are studying world populations to determine the need for protection under the United Nations Convention on International Trade in Endangered Species.
Two subspecies of N. pompilius have been described: N. p. pompilius and N. p. suluensis
N. p. pompilius is by far the most common and widespread of all nautiluses. It is sometimes called the emperor nautilus due to its large size. The distribution of N. p. pompilius covers the Andaman Sea east to Fiji and southern Japan south to the Great Barrier Reef. Exceptionally large specimens with shell diameters up to 268 mm (10.6 in) have been recorded from Indonesia and northern Australia. This giant form was described as Nautilus repertus, but most scientists do not consider it a separate species.
In literature and art 
Nautilus shells were popular items in the Renaissance cabinet of curiosities and were often mounted by goldsmiths on a thin stem to make extravagant nautilus shell cups, such as the Burghley Nef, mainly intended as decorations rather than for use. Small natural history collections were common in mid-19th-century Victorian homes, and chambered nautilus shells were popular decorations.
The chambered nautilus is the title and subject of a poem by Oliver Wendell Holmes, in which he admires the "ship of pearl" and the "silent toil/That spread his lustrous coil/Still, as the spiral grew/He left the past year's dwelling for the new." He finds in the mysterious life and death of the nautilus strong inspiration for his own life and spiritual growth. He concludes:
- Build thee more stately mansions, O my soul,
- As the swift seasons roll!
- Leave thy low-vaulted past!
- Let each new temple, nobler than the last,
- Shut thee from heaven with a dome more vast,
- Till thou at length art free,
- Leaving thine outgrown shell by life's unresting sea!
A painting by Andrew Wyeth, entitled "Chambered Nautilus", shows a woman in a canopied bed; the composition and proportions of the bed and the window behind it mirror those of a chambered nautilus lying on a nearby table.
The chambered nautilus is often used as an example of the golden spiral. While nautiluses show logarithmic spirals, their ratios range from about 1.24 to 1.43, with an average ratio of about 1.33 to 1. The golden spiral's ratio is 1.618. This is actually visible when the cut nautilus is inspected.
- Ryoji, W.; et al (2008). "First discovery of fossil Nautilus pompilius (Nautilidae, Cephalopoda) from Pangasinan, northwestern Philippines". Paleontological Research 12 (1): 89–95. doi:10.2517/1342-8144(2008)12[89:FDOFNP]2.0.CO;2.
- Broad, William (24 October 2011). "Loving the Chambered Nautilus to Death". The New York Times. Archived from the original on 24 October 2011. Retrieved 24 October 2011.
- Nautilus repertus ID:118764. Shell Encyclopedia, Conchology, Inc.
- Harasewych, M.G. & F. Moretzsohn (2010). The Book of Shells: A lifesize guide to identifying and classifying six hundred shells. A & C Black Publishers, London.
- Nautilus pompilius suluensis ID:626793. Shell Encyclopedia, Conchology, Inc.
- "Nautilus Cup". The Walters Art Museum.
- Norman, M. 2000. Cephalopods: A World Guide. Hackenheim, ConchBooks, pp. 30–31.
- Pisor, D. L. (2005). Registry of World Record Size Shells (4th edition ed.). Snail's Pace Productions and ConchBooks. p. 93.
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|Wikisource has the text of the 1921 Collier's Encyclopedia article Pearly nautilus.|