The Loonies (Lunae Jovis Magnicapites; which means "Bigheads of Jupiter's Moon") are the native sapient inhabitants of Io, a satellite of Jupiter.
Their appearance is considered quite comical by Human standards, as they have large spherical heads resting atop a five-foot long neck, about as thin as a man's wrist. They enjoy candy and produce a sound that resembles giggling. They have skinny fingers. It seems their skin can be either blue or purple.
Although barely sapient, it's clear that modern Loonies represent the degenerate descendants of what was once a greatly civilized people, for at least some abandoned cities remain to prove it.
- "The Mad Moon", by Stanley G. Weinbaum (1935)