Atmospheric beasts are cryptids that are said to reside in the Earth's upper atmosphere that seem like living creatures; however they go against all the usual rules that are applied to living things.
They fly without the need for wings and their bodies are semi-solid, often partially invisible. Many atmospheric jellyfish sightings were originally classified as unusual UFO reports, however they may be an offshoot of other potential creatures that might as well possibly reside on other planets within our own solar system or in giant gas clouds that reside in extra-terrestrial space.
Noted Bigfoot cryptozoologist author Ivan T. Sanderson devoted an entire book to the theory that many UFO sightings that have occurred, are in actuality extremely low density animals native to the atmosphere of specific planets, including that of Jupiter or Saturn. Other researchers theorize that these creatures originally came from space and decided to take up residence in our upper atmosphere.
For cryptozoologists who believe in them, they are very fragile and lightweight creatures who are either native to Earth or are aliens that came from elsewhere. If the latter theories are relevant, then atmospheric jellyfish are sometimes thought to have originated in the atmosphere of some other Solar system planet and have migrated to Earth, but they can also be thought of as originating in interstellar gas clouds of space, so that they are, in effect, alien life forms without a native planet, with the ability to "swim" through space itself.
The first known incident of where perhaps atmospheric jellyfish were reported was by noted cryptozoologist researcher Robert Gardner, and that it occurred back in the summer of 1939, when a US Army Air Force plane with 12 passengers and a crew of two aboard took off from an Army base in San Diego, California. The plane, had been flying for just about an hour before sending out a distress call. After sending out that distress signal to the base, the plane with its passengers and crew returned to the base in San Diego. Upon arrival, Army servicemen opened the hatch to the interior of the plane and were horrified when they saw that all 12 passengers and one of the pilots were dead. The other pilot, the commander of the flight, was the only person, who stayed alive, but he died in several minutes after landing the plane. Investigators from the army examined the dead military men, to discover that all of the men on board that had died had strange burn marks on their skin, but it did not become possible to find out their origin point, and what really happened on board the plane during the flight. Investigators further determined that all of the passengers onboard the plane had used their personal firearms as the hull paneling of the plane was riddled with gunshots exit points, as if the people inside the plane were trying to kill a very fast yet unseen enemy.
Also according to American researcher Charles Fort, who wrote in his work The Book of the Damned, that there were weird, jelly-like beings that live in the Earth's atmosphere. Medusa-like creatures, which had stingers and tentacles, which they used to hunt for birds. The existence of such creatures seemed to be unbelievable for a very long time, until American scientists developed a special substance known as aerogel. The lighter-than-air gelatin is a substance, the state of which is represents both solid and gaseous conditions. Researchers proposed in theory that the flesh of these atmospheric jellyfish could be made of a similar substance. The theory can be partly proven with another incident, which occurred on December 28th, 1958, in Florida. in the report, police detective Faustin Galegos found a strange soccer ball sized object outside his house. The detective took the object in his hands, but could not feel that he was holding it. It was a translucent purplish ball, and it was practically weightless. Galegos did not manage to preserve it, because it virtually melted in the air within several hours of finding it. Galegos later stated that he had an impression of holding an unknown dead or dying creature in his hands.
In a third case, a British policeman described an encounter with one of these creatures that had supposedly happened while bicycling. The thing felt like a soft blanket and smelled like mildew. After it rubbed against him, it silently floated away. It was one of the most terrifying experiences that policeman had ever had in his life.
In other various eyewitness accounts that have occurred since 1958, atmospheric jellyfish can change their density, becoming smaller, harder masses that are usually metallic in color, or they can become larger and cloudlike, even to the point of invisibility. In some reports, they may even glow. The normal habitat of these creatures are high in the atmosphere, near the very edges of space or possibly as low as the top of the tropopause, and they might die if they ever came in contact with the ground. Atmospheric jellyfish resemble clouds and may engage in behavior that is thought to be impossible for a real cloud, such as squirting a stream of horizontal water at people through "lips" or being far too mobile and animate for witnesses to believe it was just a patch of fog.