Most of the animals have limbs that help them to move around by walking.
But in case of snakes limbs are absent and they move with the help of their body muscles and scales present on their skin by pushing them on irregular surface which gave them a forward thrust, they move in a zig zag manner.
Same is the case with fishes, Insted of legs they have fins and body tructure which allows them to swin under water.
I hope this answer helps