As Smart as a Cephalopod
Class Cephalopoda consists of all the octopuses, squids, cuttlefish, and nautiluses in the phylum Mollusca. They are easy to tell apart. Octopuses are soft-bodied, and round with eight arms. In contrast, squids are bullet-shaped, possessing a stiff-internal structure known as a pen. They have eight arms and two longer tentacles. Gripping devices can be found on the arms of both squids and octopuses. Nautiluses own hard external shells and approximately ninety grip-free arms.
As with most members of the mollusk phylum, cephalopods possess a gill, a foot, a shell-secreting tissue called the mantle, a toothed, tongue-like radula, and have possessed one or more shells in the past. In fact, the mantles of the coleodian cephalopods overgrew the shell during evolution to produce the first true endoskeloton (Dando and Burchett, 1996). Today, the mantle cavity in squids and octopuses allows them to move by jet propulsion. The cavity fills with water and can only escape via a tube-like siphon. The siphon bends, the mantle compresses, and the water shoots from the siphon sending the animal either forward or backward (Milne, 1995).
All cephalopods are carnivores. Squids feed mainly on the teleost (bony) fishes. The prey is brought within reach of its beak-like jaw, where large pieces of tissue are torn off by the radula and swallowed in the buccal cavity. Octopuses favor crabs, inject them with a toxin released by the jaws or salivary glands. This immobilizes the prey so that it can be flushed with a variety of enzymes. Octopuses will then ingest the partly digested flesh. As for nautiluses, they are scavengers, which roam ocean bottoms in search of decapod crustaceans with their multitude of tentacles. They feed on their prey in a fashion comparable to that of a squid (Dando and Burchett, 1996).
Cephalopods have acquired additional features over the course of their evolutionary history. The most notable include large image forming eyes, which are connected to the largest brains witnessed in any invertebrate. These physical characteristics in combination with their behavior lead some people to believe that cephalopods are the most intelligent invertebrates. Graziano Fiorito and Pietro Scotto showed in a recent study that octopuses learn simple tasks, such as choose the red ball over the white ball, and receive an award, by watching other trained octopuses perform the tasks (Milne, 1995).
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