The eight sinuous tentacles, the fleshy body, the bulb-shaped head: making the octopus one of the most interesting animals of all the seas would simply be enough for the external appearance. But it is the internal organs that reserve many surprises. For example, not everyone knows that cephalopods have not one, but three hearts: two to pump blood to the gills and one that sends richly oxygenated blood circulating in the rest of the body. The blood of octopuses, like that of other molluscs, consists mainly of copper (and not iron). In contact with oxygen, therefore, it becomes blue and not red.

If followed, the octopus is able to move very quickly, expelling water from a funnel-shaped siphon on the side of the head. Found a shelter, it easily slips into it and, if things go wrong, it is able to lose the tentacle to which the predator is clinging (usually a shark, a dolphin or an eel). That limb will then be automatically regenerated.

In some cases, the octopuses under attack emit a cloud of dark ink from the siphon to confuse the enemies and gain the time needed to escape. While the intruder follows the dark splashes that move in the water like tentacles, convinced that the black indicates the presence of the cephalopod, the octopus changes color, is tinged with white and is given to the stain. According to ethologists, the ink would contain some substances that inhibit the sense of smell of the predator, making it more difficult to identify the fugitive.

Thanks to particular pigmented cells, the octopus can quickly take on the appearance of any element nearby, be it a rock, a sandy bottom, a coral reef or even another animal (see the video of the mimetic octopus). In the picture, a specimen of octopus with southern blue rings (Hapalochlaena maculosa), among the most poisonous creatures of all the seas. In his case, bright coloring has a purpose that is anything but mimetic. When the mollusc is agitated, the blue spots become even more visible, as if to warn the enemies of its ability to inject deadly neurotoxins.

From still the octopuses of the species Macrotritopus defilippi are perfectly camouflaged with the sand of the Atlantic seabed. But when they move, in order not to risk being attacked by predators, they put into practice an excellent technique of "acting". Standing well on the ground, they join the tentacles behind them and move forward imitating the movements of a species of tropical sole that lives in their same habitat: the Bothus lunatus. Seeing them, the enemies think it is a real fish, with lots of bones, therefore more difficult to bite. And let it go. See also the imitation video:

The suckers of the octopus (here under the electron microscope) are arranged in rows of two on each tentacle. Each of them is coated with chemoreceptors - nerve endings responding to precise stimuli - which allow the cephalopod to explore the surrounding environment and perceive the taste of the food it eats.

Tentacles and suction cups are also used during coupling. The males have a modified arm, called ectocotyl, which they use to transfer the sperm into the cavity of the female's mantle. In some species, this arm detaches during mating, remaining in the female's body. The first naturalists who found it, in the nineteenth century, in the body of some female octopus, mistook it for a parasitic worm.

Although it is difficult to choose between eight tentacles, octopuses also seem to have a favorite limb. Although all their appendages are more or less equivalent and do not have particular specializations, cephalopods seem to prefer one or a combination of two or three tentacles when it comes to exploring a new cavity or manipulating objects. In the photo, the favorite tentacle (perhaps!) Of an octopus of the Octopus tetricus species, widespread in the Indo-Pacific seabed.

Tires, cans and bottles are among the waste of human origin chosen by the octopus as a refuge. But this mollusk also has an excellent relationship with closed bottles. If placed in front of a container with a cap, containing a shrimp, the cephalopod is able to open it to reach the booty with the tentacles (see photo).

The ability to use tools appropriately is one of the features that make octopus unique among all molluscs. A group of researchers from the Museum Victoria in Melbourne, Australia, observed about 500 octopuses of the species Amphioctopus marginatus for 500 hours while collecting the coconut shells thrown into the sea by the natives near the coasts of the islands of Sulawesi and Bali. The shells, recovered from the sand, were transported by the animals and used to repair the shelters from the predators.

Watch a video of an octopus grappling with the transport of a coconut:

What is surprising about the eye of the octopus is that, although it has evolved separately from that of man, it has incredible affinities with our organ of sight. So much so that some scholars quote it as an example of how evolution sometimes chooses the same path even in two species with completely distinct origins, only because it is the most practical way. The octopus eye is provided with cornea, crystalline, vitreous humor, iris and retina. Unlike our crystalline lens, which changes shape to bring the image into focus but remains at a fixed distance from the retina, the cephalopods one always maintains the same conformation, but depending on the necessity it approaches and moves away from the retina.

It also appears that these molluscs have an excellent color vision. The particular sensitivity to color tones was also one of the hypotheses put forward - but also disputed - to explain the alleged ability of the octopus Paul to "predict" the football victories at the 2010 World Cup.

While the male can boast several partners, the female giant octopus octopus (Enteroctopus dofleini) only mates once in life. The care of unborn children, in fact, will require a total energy expenditure, indeed … lethal. Once a shelter has been chosen, it puts an average of 50, 000 eggs per brood, arranging them in "bunches" of 200-300 items at a time. The hatching will last from 150 days to a year, depending on the temperature of the water (cold bottoms prolong the process). All this time the mother will guard the brood, defending it from predators and even forgetting to feed. He will die during or just after the birth of his young.

It will also be small but do not doubt its sense of orientation. This octopus from New Zealand will have no problem finding its way home: after all it has been shown that cephalopods are able to move their tentacles inside ad hoc mazes in order to reach a succulent booty. It was already known that these invertebrates manage to arrive with their tentacles at food hidden in very narrow cracks between the rocks. Laboratory experiments have shown that they can orient the movement of the tentacles in coordination with the vision: a sign that their ability to get out of a labyrinth does not depend solely on sensory faculties but is a further sign of their intelligence.

Beauty is not everything, but this scorpion fish (Scorpaena scrofa) does not even shine in sympathy. Like the other members of the family to which it belongs, that of the Scorpionids, it is in fact endowed with one of the most powerful poisons in the marine world, which injects into its prey through one of its dorsal spines. But no matter how hard he tries, the scorpion fish will never be able to equal the danger of the Australian blue-ringed octopus, the most poisonous animal in the world. It is better not to make him angry, because when he bites, this octopus injects the tetrodoxin into the victim's flesh, a poison that can paralyze and kill a man in a matter of minutes.

We talked about the power contained in the arms of the octopus a few days ago . But the small suckers they scatter around do not only serve to hunt prey and to manipulate small stones to build their nests. These cups are also chemoreceptors, or chemical receptors that allow the octopus to feel the taste of what they touch.

Thanks to a double row of suction cups on the tentacles, the octopus (Octopus vulgaris) is perfectly capable of opening a bottle of water. And when some scholars have tried to lock up a prey in a jar of which he is greedy, he opened it without hesitation, devouring all its contents.

But it is not only brute force, the octopus proves to also have considerable intelligence. It seems, in fact, that he has successfully passed some learning tests, based on visual and tactile signals. Very strange fact for a mollusk.

And even stranger, if we think that the octopus is a solitary animal. A certain ability to learn is recorded above all among the more sociable animals, which are observed and imitate each other. But this does not seem to apply to the hermit octopus …

You should have strong arms to be able to open a shell like the one in the photo held together by the force of the suction cups placed on the octopus legs.

In short, the octopus of coconuts (Octopus marginatus) is not surprising, as it has developed a curious escape strategy, in addition to the habit of occupying empty shells or coconut shells to protect itself from possible predators. He literally learned to run, the first form of submarine bipedal locomotion known, as we explain in our news (related by video).

The giant Pacific octopus (Enteroctopus dolfeini), which lives at the bottom of the northern Pacific Ocean, at a depth of over 750 meters, has a powerful weapon in the face of dangers: the gigantic splash of an ink-like substance surrounding enemies preventing them from seeing clearly on the escape route of the prey.

Despite its size (from 10 to 50 kilograms of weight distributed over 3-6 meters in length), the mollusc is very agile and moves safely on the ocean floor thanks to its long arms equipped with powerful suction cups.

You might also like: The octopus ballet Dumbo The camouflage and transformist octopus Smart as an octopus The nose … in the arms With that face a little like this The eight sinuous tentacles, the fleshy body, the head in the shape of a bulb: to make the octopus one of the most interesting animals of all the seas would simply suffice the outward appearance. But it is the internal organs that reserve many surprises. For example, not everyone knows that cephalopods have not one, but three hearts: two to pump blood to the gills and one that sends richly oxygenated blood circulating in the rest of the body. The blood of octopuses, like that of other molluscs, consists mainly of copper (and not iron). In contact with oxygen, therefore, it becomes blue and not red.