Octopuses, a brain in every arm

Octopuses only live a few years and have no contact with their parents, so they have to learn fast and teach themselves. They are the most intelligent invertebrate organisms, and studies have shown that they can solve mazes and be taught to unscrew jar lids. The nervous system of an octopus is quite decentralised: two-thirds of its neurons are in the tentacles, allowing them to behave semi-independently. The veined octopus will pick up coconut shells and use them to build a protective shelter. This makes it the only invertebrate to use tools. Octopuses also engage in play, catching and releasing objects caught in circular currents.

Octopuses, a brain in every arm

Recent research suggests those arms may have minds of their own. Studies indicate that octopus arms each have their own independent nervous system [source: Mayell]. It turns out the brain may simply delegate orders, while the arm is responsible for deciding exactly how to execute the order. Essentially this means that the brain can give a quick assignment to the arm and then not have to think about it anymore. Scientists tested this by severing the nerves in the arms from other nerves in the body and brain and then tickling the arms. Amazingly, the arms responded to the tickling just as they would in a healthy octopus [source: Pickrell].