This strange snail-like animal, about 8 inches (20 cm), is a relative of the octopus, cuttlefish, and squid. It has changed little over the past 500 million years and is considered by some to be a living fossil. It is a deep living species, capable of migrating from about 1500 feet (450 m) to approximately fairly shallow waters at about 300 feet (90 m) without internal damage or being effected by temperature changes. This seems to occur daily when they feed upon shrimps, crabs and other small invertebrates at higher levels during evening hours.
Its shell is divided into a various number of compartments depending upon its age - about 4 as a newly hatched specimen and about 30 compartments in an adult stage. As it ages, its body moves to the outer compartment areas, leaving the most inner areas/compartments vacant, except for a gas, which serves as means to control its buoyancy. They swim by pulling water into the mantel cavity within the shell and forcing it out a muscular siphon under its tentacles. By controlling the direction of the outflow, it can swim in any direction. Its darker top shell makes it more difficult to see from above, and its lighter bottom shell makes it more difficult to see from below. Nautilus belauensis, N. macromphalus, N. pompilius and N. stenomphalus are among the known existing species.