Animal swimming styles
Don't know whether it was ever investigated, but I'm pretty sure, that frogs can in principle swim upside down (e.g. when escaping from predator), but they normally do not do it.
One example of alternative swimming styles in animals is provided by some munnopsidid isopod crustaceans. Several genera are pelagic and have very elongated forelegs equipped with rows of setae and paddle-like hindlegs (see Marshall &amp; Diebel 1995 and Giver 1998):


the forelegs are used to "walk" in the water column
the same legs can be stretched out for passive parachuting
the hindlegs are used for backward swimming



Below is a photo of a parachuting specimen. And here is a very nice video of a backward swimming specimen.



Foto by Karen Osborn from here