For a long time animals like the one on the left were to be imagined floating in Furaha skies. They all had in common that they used the lighter-than-air principle to fly, something no animal on Earth has mastered. Unfortunately, doing the math properly made me doubt whether such animals are possible, at least with a gravity and atmospheric qualities like those of Earth - and Furaha!
So the animal here is suspended in between my desire to have ballonts (a word I designed to mean ballooning life forms) on the planet and the urge for it all to be possible. At present rationality is winning, so there is no zeppeloon on Furaha, alas...
While it was permissible, the zeppeloon was the largest of Furahan ballonts. It could change the colour of its skin, influencing the amount of light absorbed or reflected. The less light it absorbs, the colder it becomes. As a result, the volume decreases, and the zeppeloon slowly sinks. Darkening the balloon will result in a rise. Zeppeloons were mostly to be found drifting high in the air, almost in a state of suspended animation, their minds as blank as their appearances.

There is a good reason why balloons designed to carry the weight of one or more humans on earth on earth have to be large: each liter of gas in the balloon can only lift a tiny amount of mass. At first I had thought that I could get away with that by giving Furaha an atmosphere somewhat denser then Earth. If this sounds contra-intuitive, that is probably because it is. Then again, there is no rule saying that science has to be intuitive. Read the blog posts on the mathematics of ballonts to find out. This one tells the story why bigger is better for ballonts; another post dealt with how much an increased atmospheric density affects balloon size. I then looked for a home for ballonts far away from Furaha, in the dense atmospheres of gas giants; even there, nature conspired against them, as the gases there are so light that you still need an immense volume to lift anything.

The only place I have not looked yet, or rather, that i have not written a post about, is terrestrial planets with crushingly dense atmospheres. They are apparently the only place where you could get a ballont of a less then gigantic size. Unfortuantely, the circumstances there will be alien in all other aspects as well.
Mind you, humans make balloons, so there is no rule than ballonts cannot exist. They must be large though, and that creates the interesting problem of procreation, as it seems that the life cycle cannot contain a small ballont: it will not fly. So either the animal must start on the ground or in the water, and grow its balloon slowly, or it must bud or in some other way start life, large already.