The chambered nautilus lives in tropical waters extending from the Andaman Sea east to Fiji and from southern Japan to the Great Barrier Reef. This animal usually lives where the slopes of coral reefs descend into deep waters. During the day, it resides in dark cool waters at depths from 900 to 2,000 feet and ascends to shallower waters (300 to 500 feet deep) at night to feed.
Chocolatey-brown zebra stripes adorn the nautilus's smooth, white shell. It expands its living space as it grows, adding internal chambers in a perfect logarithmic spiral coated in mother of pearl. The body is situated in the last chamber, and about 90 slim tentacles and a large eye peer out. The tentacles, which bear little anatomical resemblance to the suckered tentacles of squid, function mainly in smelling and manipulating food. When imperiled by predators, the nautilus withdraws into its armor and seals the door with a tough, leathery hood.
The nautilus has an unusually long life span for a cephalopod. It takes several years to reach sexual maturity and may live more than 15 years.
Octopus, sharks, triggerfish, and turtles can penetrate the nautilus shell.
At night, nautiluses ascend to shallower waters to scavenge for hermit crabs, fish, and the exoskeletons of molting crustaceans. They locate food by smelling the ocean currents for traces of dead or dying prey.
Nautiluses will reproduce annually once they've reached sexual maturity. Four modified, fused tentacles form the male sexual organ, the spadix. The spadix passes sperm to the female during mating, which can last up to 24 hours. The female fertilizes about a dozen eggs and deposits them one at a time or in small groups throughout the year. The eggs measure more than an inch in length, making them among the largest of invertebrate eggs. They have an exceptionally long incubation time, ranging from nine months to over a year. No one has ever seen nautilus eggs in the wild so little is known about the environment in which they are laid.
The nautilus's graceful shell has made it an attractive commodity for the commercial shell trade, and Nautilus pompilius is the most commonly sold species. Traders from Indonesia, Fiji, and the Philippines capture nautiluses using baited traps. Conservation concerns have been raised due to nautiluses' slow rate of reproduction. In Indonesia, it is illegal to export nautiluses.
Nautiluses first appeared about 500 million years ago during the Cambrian Explosion—they were jet-propelling themselves through ancient seas 265 million years before dinosaurs inhabited the Earth. Nautiluses are described as living fossils because they have remained virtually unchanged for millions of years. The horseshoe crab, which has been around for 300 million years, is another example of a living fossil.