The Galileani are all related, descended from the same root stock - Callistans - and evolving after colonizing the other three moons long, long ago. Galileans are about the same level of civilization as Martians, having started at about the same time.
Callistans, and thus all the Galilieani - evolved from something very like our Macrochiroptera, the great fruit bats, and are certainly of the same order. They are large and fragile, having evolved in the very light gravity of the Galilean moons, which is less than half that of Mars.
Galileani stand one and a half times as tall aa Martians, averaging 3 meters tall with a wingspread about the same. They are too weak to fly in Martian or Mercurial gravities, and too fragile to even stand in Earth or Venusian gravities for any meaningful length of time.
As in the Macrochiroptera, Galeliani arms have evolved into wings with thumb hooks. The feet, however, have become foot-hands, nearly as nimble as a human hand. There is a short tail, webbed to the inner legs, to aid in flight. The legs are longer than in Earth fruit bats, and more flexible, allowing the foot-hands to reach up over the head.
Like the Macrochiroptera, Galeliani have good hearing, but do not use echolocation. Their eyesight is excellent and binocular. They have a good sense of smell as well. They eat over-ripe fruit and flower nectar.
Ioans are the smallest and least furry of Galileani. Io being the warmest and heaviest of the Galilean moons, they have lost most of their fur, retaining only a mane about their heads and a strip down their backs, all else bieng naked of fur.
Europans are lightly furred all over, and are specialized for drinking nectar. Their tongues are very long and tubular and their muzzles are longer and narrower than the other Galileani.
Ganymedians are much like Europans, with a shorter, broader muzzle and shorter tongue than their kin. Their tails are longer than other Galileani, with most of its length being free of webbing.
Callistans are bigger and furrier than other Galileani, with a very thick mane, and larger jaws for penetrating the thick-husked Callistan fruit.