The Star Balloons are jellyfish-style creatures floating in the galaxy for the last 680 million years.
Star Balloons resemble the Jellyfish on Earth with long tentacles hanging from their undersides and an extremely large head that inflates with helium whenever the creature approaches helium-rich nebulae. They measure 600 meters tall and 100 meters in width and length. Their tentacles allow for touch, the only sense they have. They have no eyes but long tubes tunnel into their inflateable heads that let helium through. Unlike most creatures, the Star Balloons do not breathe; instead, their organs are filled with oxygen to keep them functional.
The Star Balloons evolved and developed roughly 680 million years ago but, of course, on a planet. The planet is Tajia, an ice giant smaller than Jupiter with several moons. They used to be the habitat for hundreds of other species, most of them insects, larger than those found on Earth. On a gas giant, asteroid and comet impacts would be far more frequent which means mass extinctions were also more common. Lightning is 100,000 times more powerful, which allowed for the development of lightning-proof skin to avoid their extreme energy.
Star Balloons measurable lifespans are predicted to last for 20,000 years, far longer than any creature ever discovered. At only 500 years into their life, they can begin floating independently, however, some do group together for merely survival reasons, most importantly, reproduction.
They have developed extremely thick skin that deflects small asteroids from their heads, leaving their undersides and tentacles vulnerable. Young Star Balloons have thin skin but it slowly develops over their life time. Their skin allows them to photosynthesise whenever they encounter stars at less than a light year.