The environment on gaseous planets like Jupiter and Saturn is so inhospitable that the possibility of life is slim. Still, at certain altitudes in their atmospheres, there do exist chemicals that are necessary for some sort of exotic life form.
The atmospheres of gas giants consist mostly of hydrogen and helium, but also contain elements necessary for life to survive, such as oxygen, carbon and nitrogen. The temperatures are warm enough and flashes of lightning provide energy that drives the chemical reactions needed. Life can only survive in the upper atmospheres, as pressures and temperatures rise swiftly with depth.
Under such conditions, life evolves to float using gas-filled buoyancy structures. The giant jellyfish-like organisms feed on organic debris, or other life forms like aerial plankton, using tentacles or by ingesting through scoop-like openings. They themselves are being hunted upon by jet-driven manta-like gliders.
Some examples of the aerial plankton featuring gas balloons as buoyancy:
JumpGate to Part IX of the galactic Zoo: