Nautilus - Pretty Shell, Aqua-Propelled
The Nautilus is a family of sea creatures which have seemingly made their way into today's oceans from a rift in time. Nautilidae are protected by smooth whorled shells which shield their soft bodies from predators. Like other cephalopods (octopus, squid, etc.), the nautilus have lots of tentacles - sometimes up to 90. They are the only cephalopods currently living that have an outer shell. Their heads are large, and have nine teeth to help crush and shred their scavenged meals, which includes the discarded shells of lobsters and hermit crabs; but nautiluses will also eat just about any discarded carrion they come across. This habit has served them well - scientists use fossil data to estimate that this species has not changed significantly in millions of years.
Nautiluses "swim" in an amazing way, using a complex inner plumbing system, they draw water into and out of their shells, propelling them forward, up or down. While the sea water is inside of the nautilus' living chamber, they take the salt from the water and diffuse it into its blood. In order to adjust their buoyancy, the nautilus uses osmosis, allowing water to pass through their membranes and shells - but this limits the depth at which the nautilus can live, any deeper than 2,600 feet (800m), a hapless nautilus can implode and die instantly.
Though scientists once believed that these ancient creatures had very limited intelligence, studies now show the presence of memory and an ability to improvise and change behavior relative to changing stimuli. Most species of nautilus are about 8 inches in diameter (20cm), but one particular dwarf species has a shell averaging 115mm!