Moon Crabs have great, big paddles on the end of each of their thick, rather flattened legs.
They can use them to swim if they want, but what they really like to do is use their feet like shovels to bury themselves in sand at the drop of a hat.
Also they use their legs to add a bit of colour to their otherwise drab, sandy appearance. If you got shovels for feet, flaunt it. I guess.