NAUTILUS

Nautilus in Greek means 'sailor' &
is the common name of these marine creatures.
Having survived relatively unchanged for millions of years,
nautiluses are often considered "living fossils.

They have a prominent head & up to 90 tentacles but with no suckers.
But they are retractable. They also have 9 teeth & two pairs of gills.
Nautilus tentacles differ from those of other cephalopods. Lacking pads, the tentacles stick to prey by virtue of their ridged surface. They have a powerful grip. Attempts to take an object already seized by a nautilus may tear tentacles away from the creature, which remain firmly attached to the surface of the object.

Two pairs of tentacles are separate from the other 90-ish, the pre-ocular and post-ocular, situated before and behind the eye. These are more evidently grooved, with more pronounced ridges. They serve an olfactory purpose for foraging, locating or identifying potential mates.

Unlike many other cephalopods, they do not have good vision; their eye structure is highly developed but lacks a solid lens. They have a simple "pinhole" eye open to the environment.

In order to swim, it uses jet propulsion.
The nautilus draws water into and out of the living chamber.

Nautiluses reproduce by laying eggs. Females attach the fertilized eggs to rocks in shallow waters, whereupon the eggs take eight to twelve months to develop until the (1.2 in) juveniles hatch. Females spawn once per year.

The lifespan of nautiluses may exceed 20 years, which is exceptionally lengthy for a cephalopod.

Nautiluses are predators that feed mainly on shrimp, small fish and crustaceans, which are captured by the tentacles.
Due to the limited energy they expend in swimming, they only need to eat once a month.

Nautiluses are the sole living cephalopods whose bony body structure is externalized as a shell. The animal can withdraw completely into its shell and close the opening with a leathery hood formed from two specially folded tentacles. The shell is coiled and pressure resistant, imploding at a depth of about (2,600 ft). The nautilus shell is composed of 2 layers: a matte white outer layer, and a striking white iridescent inner layer. The innermost portion of the shell is a pearlescent blue-gray. The osmena pearl, contrarily to its name, is not a pearl, but a jewelry product derived from this part of the shell .
Internally, the shell divides into camerae (chambers), the chambered section being called the phragmocone. The divisions are defined by septa, each of which is pierced in the middle by a duct. As the nautilus matures it creates new, larger chambers, and moves its growing body into the larger space, sealing the vacated chamber with a new septum. The chambers increase in number from around four at the moment of hatching to thirty or more in adults.

The shell coloration also keeps the animal cryptic in the water. When seen from above, the shell is darker in color and marked with irregular stripes, which helps it blend into the dark water below. The underside is almost completely white, making the animal indistinguishable from brighter waters near the surface. This mode of camouflage is named countershading.

The nautilus shell presents one of the finest natural examples of a spiral.