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    Nautilida

    Living relics of a bygone era still drifting through today’s oceans

    A fascinating order of marine animals that include the living nautiluses—the only surviving members of an ancient lineage of shelled cephalopods that once ruled prehistoric oceans. These creatures are often called “living fossils” because they have changed very little over the past 500 million years. With their elegant spiral shells, deep-sea lifestyle, and slow pace, nautilids offer a rare glimpse into what ancient oceans might have looked like. Today, they are found in the Indo-Pacific region, especially around coral reefs and deep slopes near places like the Philippines, Papua New Guinea, and Australia.

    What makes Nautilida unique among cephalopods is their external shell, which is divided into chambers. The nautilus lives only in the outermost chamber, while the inner chambers are filled with gas that help control buoyancy. This allows the nautilus to rise or sink in the water without using much energy—like a natural submarine. Unlike their fast-swimming cousins like squids and octopuses, nautiluses are slow-moving and rely on jet propulsion by squirting water through a siphon to navigate the ocean depths, usually staying between 100 and 500 meters deep, though they can go much deeper.

    Anatomically, nautiluses are also distinct for having dozens of small, sucker-less tentacles (up to 90!), which they use to grasp prey like small fish, shrimp, and carrion. Their eyes are relatively primitive compared to modern cephalopods—they function more like a pinhole camera, without a lens—yet they can still navigate well in the dim light of the deep sea. Another cool fact: nautiluses have a protective hood they can close over their soft body when threatened, tucking into their shell much like a turtle does. This defensive ability is something their soft-bodied cousins lost long ago.

    Despite their ancient success, nautiluses are now facing modern threats. Their beautiful shells have made them a target in the shell trade, and overfishing combined with habitat loss has led to population declines. Because they reproduce slowly—laying only a few eggs each year and taking up to 15 years to mature—nautiluses are especially vulnerable to overexploitation.