nautil

Nautil, more commonly known as the nautilus, is a term used for the cephalopod mollusks in the subclass Nautiloidea, especially the living genera Nautilus and Allonautilus. Extant species inhabit the Indo-Pacific, primarily on shallow continental slopes and reef habitats at depths ranging from about 100 to 500 meters, though they can move to greater depths at times. They are characterized by an external, planispirally coiled shell divided into gas-filled chambers; the animal resides in the outermost chamber and uses the siphuncle to regulate buoyancy by adjusting gas and fluid within the chambers.

The body is reduced with a cluster of large, retractable tentacles—typically around 80 to 90—that lack suction cups and are used to seize prey. The eyes are simple and lack the complexity of more derived cephalopods. The shell interior is nacreous, a characteristic feature of nautiloids.

Nautils are slow, nocturnal predators and scavengers feeding on crustaceans, carrion, and small fish. They move by gentle jet propulsion and vertical migrations.

The nautilus has a lengthy fossil record dating back more than 500 million years, making it one of the few surviving lineages of ancient cephalopods; living nautilids are often described as "living fossils." They reproduce by laying eggs; growth and maturation are slow, contributing to vulnerability to overfishing.

Nautilids are harvested for their shells and meat; populations have declined in some areas due to collection and habitat disturbance. Protection and management vary by region, and some species are considered at risk.