- You may be looking for Neptune, the Sea-God.
Neptune was settled by Humans from Earth in the 23rd century. At first, these Neptunians relied on special pressurized habitats to survive in the gaseous atmosphere. Over the following generations, the descendants of these colonists gradually adapted to the atmosphere until they had gained limited control of their bodies. These people were able to become as flat as a sheet of paper to lessen the effect of the dense atmosphere.
In the 30th century, because of its' heavy atmosphere, there were very few visitors to Neptune. Those who did come to this planet were forced to remain in special pressurized habitats or risk being crushed to death. If a member of an oxygen-breathing race remained unprotected on Neptune's surface, he would begin to die.
- Neptune first appeared in Mystery In Space # 1 (May 1951).