Sky Jellies

Sky Jellies, in their medusa phase, are colossal "jellyfish"—the size of whales—which have specially adapted to take to the skies.   These cnidarids have a complex life cycle which includes both sexual and asexual phases: with the medusa being the final sexual stage of it's life. When two medusae collide in their air, they exchange sperm to fertilize their eggs; then when they next find themselves above a large body of salt water (preferably coastal regions) they descend and release thousands of eggs which develop into larval planulae, become polyps, bud into ephyrae, and then eventually transform again into adult medusae. If the Jelly cannot find a mate then it will reproduce asexually instead, creating clones of itself using the unfertilised eggs instead. The longest recorded lifespan of a Sky Jelly was 20 years, but they are presumably biologically immortal, so long as they survive the hazards of life.   The medusa phase of the animal has a specialised series of chambers in it's stomach, which form rings around the body, and which can be independently filled or deflated with a flammable gas—lighter than air—that it's stomach lining is somehow able to produce merely from passing through, water, rain, or clouds. This lifts it out of the water and into the air!   The Sky Jellies primarily feed on aeroplankton and insects, but will eat just about anything that get caught in it's stinging arms if they are light enough: including leaves, seeds, and petals blowing in the wind, but also small birds and bats if they're unfortunate enough. They are know to sometimes even pick up or hold on to larger objects—or creatures—to act as ballasts in strong winds if they think they cannot raise themselves up above the cloud layer fast enough. This is when a Sky Jelly is it's most dangerous to the average person, since the creature's arms and tentacles are paralysingly venomous (though not inherently deadly). The Jellies can effuse a small amount of air quickly to push themselves in a certain direction, and they are almost always pulsing and undulating their whole bodies which give them some measure of fine control over their locomotion. They are otherwise very passive though, mostly going where the wind currents take them; descending or rising up as they desire.   And these animals do think. They are perhaps the smartest known cnidarids in the world, and perhaps one of the smartest non-sapient animals in-general: on par with the intelligence of an octopus. This is especially impressive considering they don't technically have brains; just a neural net embedded in their mesoglea. They have eyes all over their bodies, on the ends on most tentacles and one on their bell-shaped bodies too, which gives them a 360* view of everything around them. Scholars think they are related to the Anemone Men (another smart type of cnidarid). Some people even say they are telepathic! And there are all sorts of stories about glowing discs carrying livestock and shepherds off in the night. They can also bioluminesce—it turns out—which seems to be a rudimentary form of communication used at night.   Their epidermis is thick, dry, and rubbery—allowing them to deflect simple projectiles or fast flying birds—and they are almost invisible in strong daylight against the indigo sky, making them sometimes blend in with the clouds. In hot weather they fold their arms up inside themselves, which helps to keep their insides moist. If they dry out and heat up too much they will die but their bodies seal closed around the stomach and they float ever higher into the sky, until they burst. If they get too cold they shrivel up and cannot produce their floating gas anymore and begin to sink. When they are falling they will try to aim for water, but they can't aim themselves very easily until their arms are within reach of some treetops. Their lives are perilous, but by carefully controlling the gasses inside them they can avoid most problems. Lightning is their only true enemy. If a Sky Jelly is struck by lightning it will instantly explode, and this is a very dangerous thing to be standing beneath! (It's tendrils will still sting, for several days after death).   A whole Sky Jelly corpse can be used as a hot air balloon; but the dead ones do not produce the levitating gas. There are legends of people taming live ones, but no one believe them.