What is "chambered nautilus"

n. 1 A marine mollusc, of the family ''(taxlink Nautilidae family noshow=1)'' native to the Pacific Ocean and Indian Ocean, which has tentacles and a spiral shell with a series of air-filled chambers. 2 A nautilus, (taxlink Nautilus pompilius species noshow=1).

n. cephalopod of the Indian and Pacific oceans having a spiral shell with pale pearly partitions [syn: pearly nautilus, nautilus]

The chambered nautilus, Nautilus pompilius also called the pearly nautilus, is the best-known species of nautilus. 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.

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 tentacles with no suckers, which is also different from other cephalopods. 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.

, scientists have become alarmed at declining populations of nautilus resulting from overfishing, and are studying world populations to determine the need for protection under the United Nations Convention on International Trade in Endangered Species.