Squirtle is a short, tailed bipedal Pokémon. However, it has also been shown to be able to walk on all fours. They resemble a light blue turtle with their most notable feature being the hard shell on their back. This shell forms and hardens on its back after birth. They could perhaps be distantly related to some other turtle-like Pokémon, such as Torkoal and Turtwig, but Squirtle seems to only be closely related to their evolutions. Three digits are located on each hand and foot.
Squirtle's shell is an extremely helpful defensive tool. They can withdraw into the shell to block physical attacks. Their smooth, hard shell and head also aid them in other ways, such as minimizing their resistance in water to increase their swimming speed, and allowing them to launch attacks like Rapid Spin and Skull Bash.
Squirtle is a natural-born swimmer. However, due to their size, it's easier for them to transport something small (like a Pikachu) than to carry their Trainer.
Their jaws may not look like much, but they are strong enough that a Squirtle can learn to use a Bite attack.
Squirtle's tail seems to resemble that of a squirrel's tail, which allows them to use moves such as Tail Whip and Aqua Tail.