Squids have 8 arms, and have a blueish skin. They have teeth that are under the head. Although the are called Squid in game, compared to real life Squids look like Octopuses.
When Squids move, they flap their tentacles behind them. They even do this on land. Squids like to go toward light, and are most commonly found in small lakes. In the lakes you can easily kill them with a sword in 3 hits. Squids can also go against currents, unlike other mobs.