Since 1970 the Aerofauna have been classified as a separate biological kingdom. While there are superficial resemblances to terrestrial and marine animal forms, these creatures represent a completely isolated evolutionary chain. Unfortunately there is no fossil record to confirm their exact relationships; specimens are crushed or disintegrate at low altitude, their cells imploding under pressure. Genetic typing shows that they are more closely related to each other than to any other living organism; the closest similarity is found in some marine protozoans, but even there the resemblance is not great. The most distinctive feature is the presence of a blue-grey photosynthetic pigment in all cells, even in animal-like species; this pigment is most efficient in the higher UV frequencies, and has not been found in any terrestrial or aquatic species. Uniquely, a by-product of this process is hydrogen, used for buoyancy.

Today approximately 250 species are known, ranging from microscopic aeroplankton to the mighty Aeromomedusa Leviathan of the East African aerial jungle. Nineteen species are commonly found over Britain and Europe. All are superficially similar to protozoans or invertebrates; none have developed bones, although some remarkably strong lightweight structures have taken their place. There are generally considered to be four main phyla, all named after the nearest marine or terrestrial equivalent; aeroplankton, aeromedusae, aeromesozoa, and aeromollusca.

The larger species retain photosynthetic pigments in their cells, but cannot generate enough hydrogen to stay aloft. The aeromedusae and aeromesozoa feed on aeroplankton for extra energy and hydrogen, and are in turn prey to the aeromollusca. In ecological terms, their distribution represents a typical pyramid of biomass; roughly twenty tons of aeroplankton per ton of primary consumer (aeromedusae and aeromesozoa), and about the same proportion of primary consumers to predators (aeromollusca).