The musical selection could not have been more perfect. As for the swimming, according to the Florida Fish and Wildlife Conservation Commission:
Some crabs swim. Most crabs, like stone crabs and spider crabs, walk or run across the bottom. However, crabs in the family Portunidae have specially modified back legs called swimmerettes. These paddle-shaped legs rotate at 20 to 40 revolutions per minute, allowing the crab to quickly swim through the water. [source]
