![]() ![]() Nautiluses are predators and feed mainly on shrimp, small fish and crustaceans, which are captured by the tentacles. The shell of the nautilus cannot withstand depths greater than approximately 800 m. In the wild, nautiluses usually inhabit depths of about 300 m, rising to around 100 m at night for feeding, mating and egg laying. The control of buoyancy in this manner limits the nautilus they cannot operate under extreme hydrostatic pressures. Buoyancy can be controlled by the osmotical pumping of gas and fluid into or from the camerae along the siphuncles. When water is pumped out, the animal adjusts its buoyancy with the gas contained in the chamber. When water is inside the chamber, the siphuncle extracts salt from it and diffuses it into the blood. In order to swim, the nautilus draws water into and out of the living chamber with the hyponome, which makes use of jet propulsion. Nautilus macromphalus is the smallest species, usually measuring only 16 cm. However, most other nautilus species never exceed 20 cm. One form from western Australia may reach 26.8 cm in diameter. Nautilus pompilius is the largest species in the genus. The radula is wide and distinctively has nine teeth. These tentacles are arranged into two circles and, unlike the tentacles of other cephalopods, they have no suckers, are undifferentiated and retractable. Nautiluses typically have more tentacles than other cephalopods, up to ninety. ![]() The nautilus is similar in general form to other cephalopods, with a prominent head and tentacles. (It is sometimes incorrectly claimed to be a golden spiral as well.) ~~The Nautilus~~ The nautilus shell presents one of the finest natural examples of a logarithmic spiral. This mode of camouflage is named countershading. On the contrary, the underside is almost completely white, making the animal indistinguishable from brighter waters near the ocean surface. When seen from the top, the shell is darker in color and marked with irregular stripes, which makes it blend into the darkness of the water below. The shell coloration also keeps the animal cryptic in the water. The number of camerae increases from around four at the moment of hatching to thirty or more in adults. The last fully open chamber, also the largest one, is used as the living chamber. As the nautilus matures its body moves forward, sealing the camerae behind it with a new septum. The phragmocone is divided into camerae by septa, all of which are pierced in the middle by a duct, the siphuncle. The shell is internally divided into chambers, the chambered section being called the phragmocone. The osmena pearl, contrarily to its name, is not a pearl, but a jewelry product derived from this part of the shell. The innermost portion of the shell is a pearlescent blue-gray. The nautilus shell is composed of 2 layers: the outer layer is a matte white, while the inner layer is a striking white with iridescence. The shell is coiled, calcareous, nacreous and pressure resistant (imploding at a depth of about 800 m). The animal can withdraw completely into its shell, closing the opening with a leathery hood formed from two specially folded tentacles. Nautiluses are the sole cephalopods whose bony structure of the body is externalized as a shell. ![]()
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