Life forming on a gas giant?

*clears throat*

Essentially, what we begin with is a gas giant, it's obviously got no surface to speak of, but different layers of gas. These gasses obviously have other particulates within them, some of them might just be organic.

What would start a journey of evolution on a gas giant would be either a sudden influx of new organic compounds (perhaps a chunk of a planet that used to have life on it?)striking the planet, or simple spontaneous changes, that prompts the existing organic compounds to start to bond together to make microbes that can float on certain compositions of gas. Enter the player.

A new game would start with a basic microbe, except you're floating amongst a layer of gas that can support you, and you will see other bits and bobs of other compounds that you can digest. As you get bigger though you sink further and further down into heavier gas layers. What is a solution to this?

Vacuoles filled with particles of lighter gasses of course. These allow you to float within a certain gas layer in the same way a hot air balloon or zeppelin uses warmer air/lighter gasses to ascend. These vacuoles could also be emptied for a burst of speed at the cost of maintaining altitude.

As microbes start to bond together, they start creating small net-like networks that share resources gathered amongst the gas, whether they be compounds to digest, or gas gathered in vacuoles. Eventually these start to become specialized, forming the first complex organisms.

An evolving ecosystem within a gas giant would likely become determined by what layer within the gas giant the organisms reside. Higher gas layers might actually become dominated by autotrophs who can get some access to the solar system's sun by climbing higher and higher amongst the layers of gas and photosynthesizing.

"Mid" layers of gas would likely be dominated by filter feeders, which could be stationary or mobile in a sort of active or passive role. Passive filter feeders would simply float along the currents of gas, using their evolved air sacs to stay at least somewhat level within their current area, and use the flows of gasses to float along. Active filter feeders however might move about and around different gas layers by using propulsion from modified air sacs that push out streams of gas, or on wings. The more active filter feeders (and other organisms that use this active method of travel) may be able to see their environment either by sense of smell (they can detect other organisms that are "up flow" of them), thermal sensing (detect another organism as it is likely warmer than the surrounding gas), or even sonar (the gas is a medium for sound to travel in).

It is in these layers that you'd also find predatory species, that likely feed on these filter feeders and use similar methods of propulsion to their prey.

Now, it is at lower levels of gas that it could get interesting. It's no doubt very dark here, but the heavy blankets of gas would also make it extremely warm. The pressures would also become immense no doubt. So, any organisms that develop here could likely be thermovores (or whatever the term would be when absorbing energy from heat sources). Granted, this could be supplemented with filter feeding, but it might also be viable at very low high density levels of gas.

Granted, this would be extremely unlikely (maybe impossible) to gain true sapience with, since there's nothing to really establish a civilization around. But there's nothing stopping social behaviors from forming amongst the clouds.