If you were to describe an alien life form you could not do better than to describe a Flying Gurnard. It walks on the bottom with it's ventral fins and uses its smaller frontal fins as hands to look for food. When it is ready to swim it unfolds it's pectoral fins and uses them to glide through the water.
Our first encounter with Flying Gurnards was on a night dive in Dominica. We had entered the water, on a moonless night, over a bed of boulders that dropped off into a sandy bottom. As we cleared the boulders our lights caught the silhouette of these alien life forms, dozens of them, suspended as if frozen in place. They appeared to be aberrations and as we slowly moved toward them they moved only enough to let us through. They covered the bottom as far as we could see in all directions and we took great delight in being accepted as we swam through and around them until our dive had to come to an end.