The Ozoa are a peculiar race. They are native to a large gas giant similar to Saturn and physically look similar to what we would call "jellyfish". Within their "head" the Ozoa contain a lifting gas their body naturally produces and regulates to keep the Ozoa afloat. The tentacles are used for propulsion and grasping. "Swimming" similar to how a squid moves through the water.
But these traits are similar to many examples of gas giant species across the galaxy. The Ozoa are truly remarkable for being "naturally" spacefarring with elderly Ozoa able to escspe the atmosphere of their homeworld.
Ozoa are born rather miniscule but throughout their lifespan the Ozoa grow to rather monstrous size with some reaching the sizes of zeplins. When Ozoa reach peak "ship size" their outer layer of skin begins to harden into a tough exoskeleton that's also airtight and to keep themselves afloat the Ozoa begin to process the hydrogen atmosphere into fuel. Which they use to eventually escape their planet.
What I'm wondering is how they would make hydrogen into fuel. The two things I'm interested in is: how do they "process" hydrogen into a fuel they can store and second how do they effectively "burn" or "light" the hydrogen without, you know, exploding?
Evolution of the species isn't overly important for the question they just did.
They have a similar life cycle to a jellyfish, but past physical appearance are very different internally.