Micah Hanks - One unique (though perhaps unlikely) theory proposed a number of times over the years deals with the idea of “atmospheric lifeforms,” as proposed by the likes of Charles Fort, Trevor James Constable, and Ivan Sanderson, among others. Essentially, this approach to various reports of UFOs supposes that some of the sightings might describe strange, atmospheric “beasts” that are essentially self-contained, energetic creatures.
Though the multitude of encounters detailing a more technological origin for UFO craft seems to leave little room for any credence to such ideas as “atmospheric beasts,” perhaps engaging in a sort of “though game” with the subject could provide insights or some merit, by virtue of considering airborne anomalies from a less conventional perspective.
Generally, the idea of an atmospheric beast in the present context would involve a creature which either weighs less than air in a given atmosphere, or which may be capable of flying by some other means of wingless propulsion. ... As strange as such an idea may sound at first, even Carl Sagan had discussed balloon-like aliens that might be capable of existing in the atmospheres of distant gas giants the likes of Jupiter....
via Airborne Anomalies: Rethinking Atmospheric Lifeforms | Mysterious Universe.
The giant mostly invisible air-jelly fish may emit Grey alien shaped protuberances as a defense mechanism when startled by a human.