This thing really is weird.
The Chambered Nautilus, Nautilus pompilius, 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. 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 chambered nautilus has more primitive eyes than some 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 have a pair of rhinophores, which detect chemicals, and use olfaction and chemotaxis in order to find their food.