The nautilus is the only cephalopod mollusk that has a true exterior shell, divided by a large number of compartments. The animal lives in the exterior compartment. The animal regulates its floating by bringing in air or releasing water. It is recognized by its spiral shell with bright drawings, and there are 5 or 6 different species. Its usual size is some 20 cm.
The nautilus is usually solitary. It is a carnivorous animal that eats other mollusks. During the day they hide at around 400 m in depth and rest on the bed. At night they come to the surface and the lower shelf of coral reefs in search of mollusks to eat. It has up to 38 tentacles, set out in two crowns, internal and external, which do not have suckers, but segregate sticky mucous to fix the prey better. The parrot’s beak jaws are sufficiently strong to break the shell of a bivalve.
Its reproduction is oviparous and like all cephalopods, it has internal fertilization.
Jules Verne used the name Nautilus to baptize the submarine in his novel 20,000 leagues under the sea because submarines, like the nautilus, flood some chambers with water to control their floating.