Gall-ant

Gall-ants are tiny creatures native to Jupiter's moon of Ganymede. They breed in moss-like Cree and lay their eggs in it. They need to breathe ammonia-filled air, and thus cannot survive on Io (where the atmosphere is mostly methane instead), even though there exists Cree on Io as well.

Appearances

 * "Tidal Moon", by Stanley G. Weinbaum and Helen Weinbaum (1938)