Chambered nautilus

Appearance

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.

The range of the chambered nautilus encompasses much of the south Pacific; It has been found near reefs and on the seafloor off of the coasts of Australia, Japan, and Micronesia.

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 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 oldest fossils of the species are known from Early Pleistocene sediments deposited off the coast of Luzon in the Philippines.

Although once thought to be a living fossil, the Chambered Nautilus is now considered taxonomically very different from ancient ammonites, and the recent fossil record surrounding the species shows more genetic diversity among Nautiluses now than has been found since the extinction of the dinosaurs. Indeed, the taxon of the Chambered Nautilus, "Nautilus pompilius" is actually a grouping of tens of different species of Nautilus under one name.

Naming

Two subspecies of "N. pompilius" have been described: "N. p. pompilius" and "N. p. suluensis"

"N. p. pompilius" is by far the most common and widespread of all nautiluses. It is sometimes called the emperor nautilus due to its large size. 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 have been recorded from Indonesia and northern Australia. This giant form was described as "Nautilus repertus", but most scientists do not consider it a separate species.

"N. p. suluensis" is a much smaller animal, restricted to the Sulu Sea in the southwestern Philippines, after which it is named. The largest known specimen measured 160 mm in shell diameter.

Food

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.