Emperor Nautilus

Nautilus pompilius is the best-known species of nautilus.

Other names: Chambered Nautilus or Pearly Nautilus.

Description

The shell, when cut away, reveals a lining of lustrous nacre and displays a nearly perfect equiangular spiral, although it is not a golden spiral. The shell exhibits countershading, being light on the bottom and dark on top. This is to help avoid predators, because when seen from above, it blends in with the darkness of the sea, and when seen from below, it blends in with the light coming from above. It has a pattern of brown and white. 

The eyes of the chambered nautilus, like those of all Nautilus species, are more primitive than those of most other cephalopods; the eye has no lens and thus is comparable to a pinhole camera. The species has about 90 cirri (referred to as "tentacles") that do not have suckers, differing significantly from the limbs of coleoids. Chambered nautiluses, again like all members of the genus, have a pair of rhinophores located near each eye which detect chemicals, and use olfaction and chemotaxis to find their food.

The shell of the chambered nautilus fulfills the function of buoyancy, which allows the nautilus to dive or ascend at will, by controlling the density and volume of the liquid within its shell chambers.

The chambered nautilus inhabits different segments of the shell as it grows, continuously growing new, larger "cells" into which it moves its internal organs as it grows in maturity.

Distribution

The distribution of N. p. pompilius covers the Andaman Sea east to Fiji and southern Japan south to the Great Barrier Reef. Exceptionally large specimens with shell diameters up to 254 mm (10.0 in) have been recorded from Indonesia and northern Australia.

Diet

As a carnivore, it feeds on both underwater carrion and detritus, as well as living shellfish and crab. Mainly scavengers, chambered nautiluses have been described as eating "anything that smells". This food is stored in a stomach-like organ known as a crop, which can store food for a great deal of time without it denaturing.

Other

All nautilus species are threatened due to overfishing for their shell, which primarily is used for jewelry and other ornamental artifacts. In 2016, they were moved to CITES Appendix II, which restricts international trade, and later the chambered nautilus was recognized as a threatened species under the Endangered Species Act.