Peter Godfrey-Smith writes Other Minds: The Octopus and the Evolution of Intelligent Life, a book about the body, the mind and the life of Octopi.

Octopi are creatures that are across the tree of life about as different as can be from humans. How different are they? Their blood is not based on iron, as ours, but uses copper to transport Oxygen, and consequently is not red from hemoglobin, but blueish from hemocyanin.

Their brain is not centralized in a single place, but sub-brains control the various arm motor systems. These are way more complex than in humans, because they are creatures of muscle without a skeleton, providing a completely different motor apparatus. On top of that, they contain a highly developed vision system that is similar to ours, but evolved independently, and a number of cells in the skin that allow them to flash complex patterns of colors in rapid succession.

In short, Octopi are basically aliens that co-evolved on our planet.

And despite their very short lifespans they are highly intelligent: They can distinguish humans and remember how different humans treated them differently in the past. They open complicated locking mechanisms, remember schedules and plan escapes, shoot lights out by aiming water spouts at switches and use other convenient tools. They can learn by observation and deduction.

How do their brains work, and what does the world look like to an Octopus? Goes extremely well with Children of Ruin

Other Minds: The Octopus and the Evolution of Intelligent Life”, Peter Godfrey-Smith, EUR 6.77.