Nautilus, Emperor Nautilus
These animals live on the sheer faces of the continental shelf and sea mounts near coral reefs in the tropical Pacific and Indian Oceans from Andaman Islands and Philippines to northern Australia and Fiji (WA, NT, QLD).Features:
As in all chambered nautiluses, this species lives in a permanent shell. Shell diameter reaches around 18 cm. The strong hard shell has a pattern of red brown stripes over a cream background. The shell is internally divided into numerous gas chambers, each joined by flesh tube known as the siphuncle. The shell has a pearly finish on the inside surface of the outer chamber. The animal lives in the outer open chamber of the shell. It has around one hundred long thin tentacles that form a ring around the central mouth. The tentacles lack suckers, instead gripping their prey with numerous regular ridges along the tentacle length. Each tentacle retracts into a protective sleeve known as the tentacle sheath. The eyes are simple sockets with a pinhole opening. They have no lens. Nautiluses swim by squirting jets of water through the tube-like funnel. The animal can retract into the shell, protecting itself with a thick leathery trapdoor known as the hood.Ecology/Way of Life:
The six living species of chambered nautiluses are the last remnants of a group that once dominated our oceans up to 450 million years ago. There were thousands of different species, some reaching the size of cars (3.5 metres in diameter). Animals like these (the belemnites were the primitive ancestors to the cuttlefishes, squids and octopuses. Today chambered nautiluses only occur in areas where shallow coral reefs are close to deeper water. They hide during the day at depths of around 400-500 metres, rising at night to shallower waters to feed under the cover of darkness. They are generally scavengers feeding on any animal remains as well as smaller live prey such as hermit crabs.
Their strong complex shell is used as both protection and as a tool for buoyancy control. The gas inside the shell is at very low pressure and the nautilus adjusts the amount of water in the chambers so that it exactly cancels its body weight. This way it can hang midwater without having to constantly swim.
Nautiluses mate by joining face-to-face, staying joined for up to 24 hours. The male passes sperm packets to the female with a special modified arm known as a spadex. The female lays single eggs on the seafloor that look like dim sims. The eggs take one year to develop with the shell of the youngster sticking out of the egg case in the last stages of development. The young are immediately independent heading off to scavenge.Interaction with Humans/Threats:
In some countries, particularly the Philippines and Indonesia, nautiluses are harvested using baited bamboo traps for the shell trade and for human consumption. Some shell traders use acid to dissolve the outer pattern layer making the whole shell pearly in appearance. There are conservation concerns about heavy fishing pressures on these slow-growing animals through the shell trade.Further Reading:
Saunders, W.B. and N.H. Landman. 1986. Nautilus: the biology and palaeobiology of a living fossil. Plenum Press, New York.
Ward, P.D. 1987. The natural history of Nautilus. Allen and Unwin, Boston.
Norman, M.D. 2000. Cephalopods: A world guide. ConchBooks, Hackenheim, Germany.
Text & map by Mark Norman; photographs by Mark Norman and David Paul.Sponsorship welcomed:
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