Chambered Nautilus
The pearly nautilus: a living cephalopod with a spiral shell, not a living fossil.
The chambered nautilus (Nautilus pompilius), also called the pearly nautilus, is the best-known species of nautilus. Its shell, when cut away, reveals a lining of lustrous nacre and displays a nearly perfect equiangular spiral, though it is not a golden spiral. The shell exhibits countershading, being light on the bottom and dark on top, which helps avoid predators. The species has about 90 cirri (tentacles) without suckers, and a pair of rhinophores near each eye for chemotaxis.
The oldest fossils are from Early Pleistocene sediments off Luzon in the Philippines. Although once thought a living fossil, it is now considered taxonomically very different from ancient ammonites, and recent fossil records show more genetic diversity among nautiluses now than since the extinction of the dinosaurs. The taxon Nautilus pompilius is actually a grouping of tens of different species under one name. All nautilus species are threatened due to overfishing for their shells; in 2016 they were moved to CITES Appendix II, and later the chambered nautilus was recognized as threatened under the Endangered Species Act.
Quick Facts
- Class
- Cephalopoda
- Order
- Nautilida
- Shell type
- External, chambered spiral
- Primary habitat
- Deep tropical reefs and continental slopes
- Locomotion
- Jet propulsion via siphon
Lore & Background
The chambered nautilus is the title and subject of a poem by Oliver Wendell Holmes, in which he admires the 'ship of pearl' and finds inspiration for spiritual growth. A painting by Andrew Wyeth, entitled Chambered Nautilus, shows a woman in a canopied bed whose composition mirrors that of a chambered nautilus on a nearby table. The Russian rock band Nautilus Pompilius is named after the species. American composer Deems Taylor wrote a cantata called The Chambered Nautilus in 1916. Nautilus shells were popular in Renaissance cabinets of curiosity and were often mounted by goldsmiths to make extravagant cups, such as the Burghley Nef, mainly for display or ceremonial drinking.
Reader's Guide
The chambered nautilus is a carnivore that feeds on underwater carrion, detritus, living shellfish, and crab, mainly as a scavenger eating 'anything that smells'. Food is stored in a crop. The species lacks a larval stage; eggs are laid in crevices or between corals and hatch after 9 to 15 months depending on water temperature. The nautilus shell of the young develops inside the egg and breaches the top before full emergence.
Chambered nautiluses are relatively long-lived and reach maturity at about 5 years old. The shell functions for buoyancy: the nautilus controls the density and volume of liquid within its shell chambers to dive or ascend. They generally inhabit depths around 1000 feet but can dive deeper, though shells slowly fill with water at extreme depths and implode at depths beyond 2000 feet. As the nautilus grows, it continuously moves into new, larger chambers, leaving smaller chambers for depth regulation.
Two subspecies are described: N. p. pompilius (the most common and widespread, sometimes called emperor nautilus) and N. p. suluensis (restricted to the Sulu Sea, much smaller). The shell's logarithmic spiral ratio ranges from about 1.24 to 1.43, averaging about 1.33 to 1, not the golden spiral ratio of 1.618.
Did You Know?
- The chambered nautilus has about 90 tentacles (cirri) that lack suckers, unlike other cephalopods.
- Its eye has no lens and works like a pinhole camera.
- The species was first bred in captivity at the Waikiki Aquarium in 1995.
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