Io is a moon of Jupiter. It is the closest of the main moons, to its parent planet and is the most volcaniccally active body in the solar system. Like the other Jovian bodies, it is affected by the force of 'Tidal Flexing' which continually reshape the planet. An area the size of africa is always changing. It is covered in sulphur geysers and is incredibly zapped with the radiation coming from the Sun, Jupiter and outer space. It is an extremely hostile planet.
Any native is single celled since Io has no constant surface. It may also have had non-native colonies in the past.