This is because the spiral shell is compartmentalized into a series of chambers. Only the first one holds the animal's body. The others are all filled with gas. An orifice in the middle of each compartment allows the gas to circulate in order to adjust the animal's buoyancy.
The loss of a few grams of matter from the nautilus's shell is sometimes enough to cause its buoyancy to increase, potentially leading to the animal's death.
To move around, the nautilus rocks back and forth, expelling a stream of water through a sort of tube or hyponome.
Each night, the nautilus rises toward the surface, most likely to escape from predators. During the day, it drops back down to feed on bottom-dwelling invertebrates that it finds by smell and catches using the short tentacles (without suckers) surrounding its mouth. Its diet mainly comprises crustaceans, which it cracks open with its mandibles. Like birds, its digestive system has a crop, where it can store its food for several days.
Unlike other cephalopods (like octopi and cuttlefish), which die after laying their eggs, the nautilus has a relatively long life cycle. It matures at the age of 10 years, then reproduces for a few more, laying a dozen or so eggs each breeding season. Mating can last up to 24 hours, during which time the two animals cover themselves with mucus. The female only lays about a dozen eggs per season. The eggs are 25 to 35 mm long and are deposited one next to the other, stuck to the substrate.
The artist on stage