I think that after Sky 1 noticed that the alien floating in the water was alive, the submarine part of Sky 1 retrieved him.

"Amphibious" typically refers to both land and water, and the Skydivers don't operate on land. But I haven't found a word specific to air and water. And in this case the difference is that the two parts of Skydiver have rather specifically different functions. The Sky part doesn't function underwater at all, and the Diver part never flies or goes on land.