A forced evolution, introducing basic lifeforms like planarian flatworms into an environment and supplying enough food materials to feed them for at least a few dozen generations while they evolve into divergent pathways based on the situation's extreme nature would be feasible. But natural evolution there is unlikely at best.

Though theoretically, a gas giant planet would have balloon like creatures. Similar to Jellyfish but instead of filling with water and filtering nutrients from microscopic sources, they'd inflate with air and absorb material straight from the air.