The common octopus (Octopus vulgaris) is a mollusc cephalopod devoid, unlike most molluscs and even its colleagues the cuttlefish and the squid, of any rigid structure – a shell, that is. This is why, besides displaying an impressive chromatic camouflage, it is also capable of behavioral camouflage through a change in shape according to the bottom type.
We often stare at it overwhelmed, especially when out of fear of our gigantic size (in proportion!) it grows wrinkles and spikes on its body.
It comes with 3 hearts and 8 arms (beware, they’re not tentacles, for these have suckers at their end!) run by two lines of suckers, it can survive up to 2 years and weigh as much as 10 kg. It can both crawl on the bottom using its arms and swim through a siphon placed near the head, through which it spits water for propulsion. When scared it uses the siphon as well, namely to splash the so-called ink, a viscous liquid made of melanin (like in this video, shot in Lampione).
It fancies crustaceans (crabs over anything else) as well as some molluscs such as the green ormer (Haliotis tuberculata tuberculata). It indeed loves to decorate its den with the latter’s nacreous shells, making itself recognizable to spearfishermen, though.
Speaking of their taste for molluscs, some octopi are indeed… cannibals. True, they can prey on smaller specimens of their own species, eating them after choking them slowly.
The octopus lives a thoroughly lonely life, seeking for its partner only when the time to mate comes.
Once she hangs the eggs cluster in a well sheltered hole, the female oxygenates it continuously “pumping” with her siphon. She never moves away from the den, so much so that she eventually dies when the eggs hatch, poor girl!
Males and females, by the way, are almost identical from the outside. Well, almost, for the male has a special arm, called ectocotile, that he uses to insert the sperm inside the female. Such an arm is usually shorter and devoid of suckers at its end.
A little curiosity: there is a funny symbiosis between octopus and painted comber (Serranus scriba). When the octopus exits the den for its raids, one or more combers would always follow it, hoping to take advantage of the left-overs. And what about the octopus, does it also gain something? Maybe. It seems in fact that the comber behavior might alert in advance the octopus about the presence of a predator, thus saving time for its escape.
But most of all them octopi are super clever beings, the most clever among the invertebrates!