chambered 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 range of the chambered nautilus encompasses much of the south Pacific; It has been found near reefs and on the seafloor off 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 (referred to as "tentacles"; see Nautilus § 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...