The nautilus is a marine mollusk belonging to the family Nautilidae. It has a distinctive spiral shell that is divided into chambers, which the animal uses for buoyancy. Nautiluses are often referred to as "living fossils" because they have existed for millions of years, with little change in their form. These creatures primarily inhabit the warm waters of the Pacific Ocean and Indian Ocean. They are nocturnal and tend to live at depths of up to 800 feet, using their tentacles to catch prey like small fish and crustaceans. The nautilus plays a crucial role in the marine ecosystem.