A large part of the octopus brain lies in it's arms
Creatures that live in the sea, even the Medusozoa (jellyfish) have nervous systems. Two-thirds of the nerve cells in the even more complex nervous system of
the octopus (a mollusk) are located in the nerve cords of its arms which makes the eight tentacles function as an extended brain (see insert). Godfrey-Smith
the author of the best-selling recent book Metazoa writes about how our nervous system developed from our early ancestors the metazoans (organisms with multiple cells), probably from the cells of corals, sponges,
and anemones that live in the sea. Each of these organisms has evolved into a form that is perfectly adapted to its environment. He describes a one-armed shrimp as follows: “Eighteen limbs and protrusions … a body like a Swiss Army knife.”
In spite of missing a claw and being surrounded by bigger, mightier animals such as mollusks and sharks — “in the land of the limbless, the one-armed shrimp is king’. The body of common fishes functions as ‘one great ear’,
catching the smallest sounds propagated in the water enabling some species even to distinguish between different melodies. Knowledge of how 'primitive' biological systems have evolved would, in his view, contribute more to the understanding of the human
brain than that of the modern digital computer.