Adhesion is achieved through the secretion of a neutral (rather than acidic) mucopolysaccharide from secretory cells in the ridges of the digital cirri.

[13][14][15] Release is triggered through contraction of the tentacle musculature rather than the secretion of a chemical solvent, similar to the adhesion/release system in Euprymna, though it is unclear whether these adhesives are homologous.

The mouth consists of a parrot-like beak made up of two interlocking jaws capable of ripping the animal's food— mostly crustaceans— from the rocks to which they are attached.[19]: p.

From the crop, food passes to the small muscular stomach for crushing, and then goes past a digestive caecum before entering the relatively brief intestine.

[20]: 56  Oxygenated blood arrives at the heart through four ventricles and flows out to the animal's organs through distinct aortas but returns through veins which are too small and varied to be specifically described.

The one exception to this is the vena cava, a single large vein running along the underside of the crop into which nearly all other vessels containing deoxygenated blood empty.

From this ring extend all of the nerves forward to the mouth, tentacles, and funnel; laterally to the eyes and rhinophores; and posteriorly to the remaining organs.

The nerve ring does not constitute what is typically considered a cephalopod "brain": the upper portion of the nerve ring lacks differentiated lobes, and most of the nervous tissue appears to focus on finding and consuming food (i.e., it lacks a "higher learning" center).

Nautili also tend to have rather short memory spans, and the nerve ring is not protected by any form of brain case.

[21] Nautili are the sole living cephalopods whose bony body structure is externalized as a planispiral shell.

The animal can withdraw completely into its shell and close the opening with a leathery hood formed from two specially folded tentacles.

A dwarf population from the Sulu Sea (Nautilus pompilius suluensis) is even smaller, with a mean shell diameter of 11.56 cm (4.55 in).

[26] It is thought that this is related to the use of asymmetrical contractile cycles and may be an adaptation to mitigate metabolic demands and protect against hypoxia when foraging at depth.

This is done in response to sudden changes in buoyancy that can occur with predatory attacks of fish, which can break off parts of the shell.

[29] The nautilus has the extremely rare ability to withstand being brought to the surface from its deep natural habitat without suffering any apparent damage from the experience.

Whereas fish or crustaceans brought up from such depths inevitably arrive dead, a nautilus will be unfazed despite the pressure change of as much as 80 standard atmospheres (1,200 psi).

188 Unlike many other cephalopods, nautiluses do not have what many consider to be good vision; their eye structure is highly developed but lacks a solid lens.

Instead of vision, the animal is thought to use olfaction (smell) as the primary sense for foraging and for locating and identifying potential mates.

[30] The "ear" of the nautilus consists of structures called otocysts located immediately behind the pedal ganglia near the nerve ring.

But the cephalopod nervous system is quite different from that of other animals, and recent experiments have shown not only memory, but a changing response to the same event over time.

The nautiluses completely forgot the earlier training 24 hours later, in contrast to octopuses, for example, which can remember conditioning for weeks afterwards.

[35] Nautiluses are sexually dimorphic, in that males have four tentacles modified into an organ, called the "spadix", which transfers sperm into the female's mantle during mating.

[36] Males have been found to greatly outnumber females in practically all published studies, accounting for 60 to 94% of all recorded individuals at different sites.

It has long been believed that nautiluses rise at night to feed, mate, and lay eggs, but it appears that, in at least some populations, the vertical movement patterns of these animals are far more complex.

[39] While nautiloids were once common worldwide, their numbers declined and their distribution became restricted to their current habitats during the Pleistocene, largely due to the diversification of pinnipeds.

The other cephalopod subclass, Coleoidea, diverged from the nautiloids long ago and the nautilus has remained relatively unchanged since.

[43][44] The family Nautilidae has its origin in the Trigonocerataceae (Centroceratina), specifically in the Syringonautilidae of the Late Triassic[5] and continues to this day with Nautilus, the type genus, and its close relative, Allonautilus.

Pseudocenoceras is compressed, smooth, with subrectangular whorl sections, flattened venter, and a deep umbilicus.

Carinonautilus is a very involute form with high whorl section and flanks that converge on a narrow venter that bears a prominent rounded keel.

[57][58] Palauans see nautili (Palauan: kedarm) as a symbol of vulnerable or fragile character from a belief that they easily die even from slight bumps on ocean rocks; hence someone who gets quickly angry after being pranked is compared to one (ng ko er a kedarm, el di metirem e metord).