We live in the midst of a fluid environment; on water, land, or even in space

It may definitely sound "insane". However, most of the cosmos is a fluid environment. Essentially, everything that exists in the cosmos lives inside of a fluid. In other words, the cosmos is an "ocean", for the most part. An atmosphere is just not dense enough of an ocean for us to swim in it. In fact, there are just about no lifeforms that can sustain themselves in the air just as we could do in the water; at least, not in an atmosphere that's as thin as Earth's. The best that life on Earth can ever wish for is to fly, or hover, just like the light butterflies, birds, etc. And, of course, there is also microscopic life which exists at elevations exceeding a phenomenal 120,000 feet. These kinds of lifeforms can actually stay up there for prolonged periods of time. We ourselves have to depend on things such as airplanes, weather balloons, and blimps to help us achieve these dreams. Now, let's think about something more tantalizing. Suppose we have a planet, on which the air is phenomenally dense, as compared to that of Earth's atmosphere. Let's further suppose that advanced life forms would, for whatever reason, need to stay above ground constantly. One reason for this, for example, would that perhaps the planet's surface has become toxic. There are probably other reasons that one could come up with for why life would evolve on this type of planet, to develop these, what I like to call "skills". These lifeforms might even need to rely on structures inside of them, which would be massive, as compared to themselves. These structures would probably be necessary, because of the fact that these organisms would rely on massive amounts of gasses to be inhaled, and later stored, inside. These structures would probably best be described as lungs. And who knows what type of gasses they would contain? It could be light gasses, such as Helium, or even Hydrogen, which have a density that's significantly less than our surrounding atmosphere. After, all, think about what weather balloons can do. When you fill them up with such gasses, they can travel incredibly high. The case with exotic lifeforms could be that, these lifeforms are made up of extremely thin membranes. And, as a result, they are likely bound to have very intricate bodies. As a matter of fact, their bodies would almost certainly be transparent, as is the case in very rare occasions on Earth, such as when we study life forms such as jellyfish, or glass frogs of South America. Now, what if we were to put the light gasses of Helium and Hydrogen aside for now? If so, then it's still really possible for lifeforms, or "jellyfish" to live in the air. So, what would it take? It has to do with the difference between air temperatures. And, the higher the temperature difference between the inside of the organism is to its outside environment, the higher the density differences are. And the organism could still float. Well, that would be, if the density of the outside environment is higher than the density of the jellyfish itself. Now. Think about ships. Ships are made to stay afloat. Yet they may sometimes weigh many tons. So, how do they stay afloat?Well, just keep that in mind for now. The density of the jellyfish would need to not just account for the inside of itself. It would also need to account for the outside as well. The density of it's whole entire self would need to be less than the surrounding atmosphere. Space itself can be thought of as an ocean. How? Well, think about when astronauts go out and explore space. They are essentially in the ocean. They are surrounded by a deadly environment, deprived of oxygen, which stretches over vastly immense distances! Their is virtually no difference when you compare the cosmic environment to that of being underwater. And, of course, you also have to contend with the fact that you can float about freely. And this is perhaps, just the same way as to how life exists on other planets...and that's just how I would like to redefine the term "extraterrestrial". Out of this world, that is.