A photo release this week by the Wildlife Conservation Society shows the New York Aquarium’s nautilus specimen, an animal that has remained unchanged for over 400 million years and which is considered a living fossil.
The Nautilida started their evolutionary history in the Lower Devonian around 420 million years ago in the Paleozoic era and were not affected by the wave of the large-scale mass extinctions of animals and plants that ended around 65 million years ago in the Mesozoic era, which wiped out their closest relatives, the ammonites and was considered the beginning of the Cenozoic era.
During prehistoric times, there were about 10,000 different species of nautilus, but only a small handful are known to survive today. Nautilus can nowadays only be found in the Indo-Pacific, where they inhabit the slopes of the coral reefs. They are the only cephalopods with an external smooth thin shell, matte white on the outside and mother of pearl inside, that is pressure resistant to a depth of about 2600 feet (800 m), although they live in a depth of only 1000 feet.
They are usually found within a range of 350 feet (100 m) to 1000 feet (300 m), living in the deeper waters and rising at night for feeding, mating and egg laying. Their development in the egg takes over a year and reaching maturity about four more years. They can spawn several times in their about 20 years of life. Their maximum size doesn’t quite reach 10 inches (20 cm) of diameter.
They have 38 arms which form a circle around the head. Above the head and arms is a leathery hood that protects the animal when it withdraws completely into the shell closing it. They feed on fish and invertebrates, as well as some carrion.
The animal creates chambers that increase in size from the inside out as it moves to occupy the outermost and biggest chamber. An adult animal can have thirty or more such chambers. A tube, the siphuncle, runs down the center of the chambers releasing a gas with which it maintains buoyancy and keeps itself in an upright position.
They use jet propulsion to swim by drawing water into the living chamber and can reach speeds of over two knots. They steer mostly by sensing obstacles and sometimes bump into them before changing course.
The nautilus is closely related to other cephalopods such as the squid, cuttlefish, and octopus as well as the extinct ammonites.
Researchers are very interested in two fundamentals of the nautilus: the incredibly strong nacre coating the inside of the shell and the highly developed pinhole eye that lacks a cornea and lenses.
Copyright © 2009 by Marine Science Today, a publication of OceanLines LLC