Nautilus pompilius - Chambered or Pearly Nautilus
Nautilus scrobiculatus - King Nautilus
The Chambered Nautilus is a living fossil, virtually unchanged for the last 500 million years. There were Nautilus before there were fish, before the dinosaurs, long before mammals, not to speak of humans. 500 million years ago, Nautilus and its larger relatives (which were up to six meters long) were the dominant predators in the ancient seas.
Nautilus are beautiful and impressive creatures. Their main feature is a large shell similar to the one of a snail, which can grow to up to twenty centimeters in diameter. It is coiled upwards. Many small tentacles come out of the entrance of the shell, as well as a funnel used for propulsion. A leathery hood on top of the tentacles can move down to cover the shell entrance completely when the animal retracts its tentacles. Just under the hood, near the center of the shell, are the eyes of the Nautilus. They are very simple eyes, as they do not have a lens but rather work like a pinhole camera.
The shell is subdivided into up to 30 chambers, with the Nautilus itself living only in the largest, foremost chamber. As it grows, its body moves forward in the enlarging shell and produces a wall to seal off older chambers. The empty chambers are filled with gas and used to regulate buoyancy. The shell is a precise golden spiral, which is the reason it looks so beautiful.
The Nautilus is white with brown patterns on the top for countershading.
Nautilus mostly live on the slopes of deep reefs in the Indian and Pacific oceans, at depths of 180 to 360 meters. During the day, some species migrate into shallower and warmer water, up to about 90 meters of depth. However, they may be found at depths of down to 500 meters. They have an unusual ability to live at different depths and temperatures, which can certainly be attributed in part to their special gas chambers. Nautilus move very slowly, at a rate of 0.45 to 0.8 kilometers per day.
Nautilus are very opportunistic eaters, preying on crabs and shrimp and scavenging on the remains of other animals. They catch their prey with their tentacles and pass it to the mouth (located within the circle of tentacles) where a beaked jaw tears it into bites. A file-like feeding structure, the radula, further shreds the food before it is swallowed.
Little is known about the mating habits of these creatures, since it is very hard to induce them to reproduce in captivity. During mating, the male holds on to the female's shell and deposits a packet of sperm into her mantle cavity with a special tentacle, which then breaks off to be regrown later.
Protected by several layers of membranes, about a dozen eggs are laid one at a time, the female attaching them to a hard surface. After a development time of twelve months, the young Nautilus will hatch. At that time it has a diameter of about 3 centimeters and its shell already consists of four chambers. Nautilus mature slowly and live for up to at least sixteen years, unlike many other cephalopods.
Threats and Protection
Nothing is known about the natural enemies of Nautilus. They do not seem to have any defenses except for their shell and camouflage, and move but slowly, yet they still have survived for 500 million years despite their comparatively slow rate of reproduction. It can therefore be assumed that they do not have many predators.
Danger from humans however is entirely another matter. The beauty of their shells has become very dangerous to the Nautilus, as they are now extensively hunted for their shells. The situation in New Caledonia is said to be catastrophic, with 10'000 live Nautilus being killed over the period of only two years! Some are also captured for aquaria. (There they may live for a long time, but they usually have problems with buoyancy and their shells become discolored.)
The Nautilus are currently not listed as a threatened species because there is no way to measure their population. Yet it should be clear that the extreme demand for their shells will greatly decimate the population if nothing is done to prevent their being caught and slaughtered. I personally believe that the living Nautilus is a far more beautiful thing than the dead and hollow shell.