From the nutritional point of view, the octopus can be considered a noble animal, thanks to its richness in proteins and low fat content.
But it's not just his proteins that are noble: we are indeed talking about a blue-blooded animal, in the literal sense of the word.
In fact, the octopus, like most molluscs, has a blood rich in hemocyanin . It is a respiratory pigment similar to our hemoglobin, but which contains copper instead of iron. When hemocyanin binds to oxygen it becomes blue, giving the octopus blood the typical color.
By the way, the origin of the expression "having blue blood" could depend on the typical pallor of aristocratic skin, a characteristic that in certain historical periods has been particularly sought after by the nobility. The paleness of the skin, in fact, was opposed to the tan of the peasants forced to work under the sun.
At the level of the wrists, the veins are so superficial that they appear under the skin, showing themselves as bluish veins. While the tan camouflages this sign, the pallor exalts it. Hence the expression "having blue blood" could derive precisely from the bluish-violet aspect that the veins of the wrists and forearms of subjects of light complexion assume.
