How is depth/atmospheric pressure planed to be used in the multicellular? Also if a planet had a very dense atmosphere would it be easier for creatures to fly or something like that?

My extremely rudimentary understanding of physics tell me that it would be easier to glide, but harder to move. So you’d get animals that could stay in the air for longer, but they’d move more slowly.


Its basically more of a “blimpy” or baloon type of flight rather than what we have on earth. This would mean flying jellyfish and the such.