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Impressive in both looks and brains, Octopus vulgaris (the common octopus) is best known as the Houdini of the tropical and temperate waters of the world’s oceans for the wide array of strategies it employs to thwart attackers and bag a meal. It can hide in plain sight, using a network of pigment cells and specialized muscles in its skin to nearly instantaneously match the colors, patterns, and textures of its surroundings. It can release an inky cloud produced by accessory glands of the gut to disorient both predators and victims alike and dull their sense of smell. Although crawling on its eight tentacles is a preferred means to ambulate, it can expel water through its ventral siphon to swiftly escape through jet propulsion. Its soft body can squeeze through impossibly small cracks (any hole not smaller than its hard beak) where predators can’t follow. If it loses an arm in a struggle, it will regrow without permanent damage, and that beak-like jaw can deliver a sharp bite powerful enough to crack hard shells and release venomous saliva to subdue prey such as molluscs and crustaceans.
Octopus vulgaris have three hearts. Two small branchial hearts pump oxygenated blood to the gills, while a systemic heart circulates it to the rest of the body. The nervous system includes a central brain and a large ganglion at the base of each arm, which controls movement. That makes a total of nine “brains.” Their blueish-colored blood contains the copper-rich protein hemocyanin, which is more efficient than hemoglobin for oxygen transport at very low temperatures and low oxygen concentrations.
Octopus vulgaris are normally solitary and territorial, settling into dens at some distance from other octopuses. This loner behavior is only interrupted during mating and spawning, as females return to isolation to brood their eggs. You can tell a male octopus from a female by looking at the tip of its third arm on the right (starting between the eyes and going clockwise). Males have a special tip on this arm that has no suckers on the last few inches. This specialized tip is visible even in immature octopus. To mate, the male inserts this special arm into the female’s body cavity. A captured male will try to protect this arm. During the entire period of spawning and brooding (which can last as long as five months at low temperatures), the female rarely leaves her mass of 100,000 – 500,000 eggs and does not eat. Instead she cares for the eggs by cleaning them with her tentacle tips, by directing jets of water through the mass, and by defending against predators. Females die shortly after the hatching of the final embryos, having lost up to one-third of their pre-spawning weight.
As the most intelligent invertebrate animal, Octopus vulgaris can compete even with mammals in solving problems, making discriminations based on visual, tactile, and chemical cues. It also remains one of the most common octopus species commercially fished for food and for the aquarium trade. Between 10,000 and 20,000 metric tons of Octopus vulgaris are caught by commercial fisheries yearly using unbaited octopus pots to attract unsuspecting octopuses searching for seemingly safe havens. It is thought that this species has a number of subspecies, but they have not yet been taxonomically classified. Research is underway to assess its genetic structure in order to correctly manage the resource and to avoid overfishing and collapsing of local stocks.