They are not big, powerful, or fast, yet nautiluses have been around for at least 500 million years. Back in the Cambrian Period (542–488 million years ago), these magnificent mollusks were some of the most successful predators in the ancient oceans. Nautiluses first appeared in the fossil record 500 million years ago. Although they have not changed much since then, their ancient ancestors grew much larger: up to 8.2 feet (2.5 meters) in size.
Today, only six known species survive, of which the emperor nautilus (Nautilus pompilius pompilius) is the largest, growing up to 8 inches (20 centimeters) long. These beautiful creatures resemble other cephalopods, in that they have a large head and a “foot” that has been modified into tentacles. However, their defining characteristic is that gloriously coiled shell, which the authors Oliver Wendell Holmes and Jules Verne immortalized in verse.
Inside the coiled shell (of a nautilus) are chambers containing air and seawater, which can be adjusted to change the nautiluses’ buoyancy. As nautiluses grow, more chambers are added (up to 30), although the mollusk lives in the outermost segment only. The shell is thin and light, but its shape and the air chambers inside make it surprisingly strong: able to resist pressure up to 2,600 feet (792 meters).
Nautiluses have an incredibly powerful grip. Once the creature attaches itself to an object, its tentacles can be literally torn off and it still won’t release its vice-like grip. The radula is a little like a toothy-rough tongue, which mollusks use to grind food. When danger strikes, the nautilus simply retreats inside its shell, using two specially adapted tentacles, called a hood, to cover up the entrance. As its vision is poor, the nautilus is thought to rely on its sense of smell to find food. Two tentacles, near the eyes, are covered in sensitive cilia, which may help them to “sniff out” prey.
Nautiluses can be found in the Indian and Pacific oceans, from the Philippines to Australia. They prefer the deeper waters around coral reefs, but usually enter shallower waters to spawn. Radiometric dating helped scientists confirm the Cambrian origins of the nautilus. Presidents Teddy Roosevelt and Woodrow Wilson believed in Darwinian evolution. This is an excerpt from the non-fiction scholastic book Sharks & Underwater Monsters by Paula Hammond. THE END