Octopus

In 2009, a veined octopus was observed carrying coconut shells and using them as shelter—the first documented tool use by an invertebrate. Octopuses can also solve puzzles, open jars, escape aquariums, and learn by watching other octopuses.

An octopus has roughly 500 million neurons, and more than two-thirds of them are distributed across its eight arms rather than its central brain. The brain issues high-level commands while each arm independently handles the details—a decentralized nervous system.