Levanian

The Levanians are sapient creatures with a huge serpentine shape and spongy, porous meat. They are native to the Earth's moon, which they refer to as Levania. They spend much time in caves, though they must come out to feed, and also enjoy sunbathing at the entrance of their shelters, ready to get in should the weather become too harmful. Short-lived, their entire life span can last for less than a Lunar day (which is equivalent to an Earth month). By unknown means they are able to travel to the Earth, apparently assuming a human form, and also to "lift" humans over to their own world, although the journey can be dangerous and tiresome. They appear to be a peaceful people, with strong scientific curiosity.

Since Levania is tidally locked, each day there lasts a month, and the flora and fauna need to deal with extended alternated periods of burning day and chilling night. The inhabitants often make use of subterranean refugees, such as cave systems and grottoes, to protect themselves from the extreme weather. They refer to the Earth as Volva and divide their world in two hemispheres, one of which is constantly facing Volva and the other is perpetually opposite from it. For those who live in the midway line or frontier, Volva always appears like a huge bright mountain in the horizon. The Levanians utilize Volva in their understandings of time passage, like the Earthlings use Luna; but also as a geographical delimitation, since its status as a fixed point in the sky allow for its manifestation in the sky alone to be usable to determine one's position on the globe. The Levanians use Volva's phases to mark the passage of time, but since Volva is large, bright and fixed, they can also observe its continents and their rotation, and thus can use Volva to distinguish Earth-days, these being very useful since the sun to them takes an entire month to move from rise to rise, thus being useless for marking relatively short periods of time. Oddly, the Earth-day is referred by them as an hour, and is their only uniform measure of time.

On the Subvolvan region, facing Earth, the climate is much more adequate and the water remains mostly liquid. This happens due to the presence of Earth in the sky reflecting sun rays during the two-weeks-long night, and the fact that they are further away from the sun during day. The creatures of the dark side are enormous, short lived and nomadic, always moving along in search of food on their cold arid habitat. Many of these creatures are amphibious, and retreat deep underwater when possible.

Behind the scenes
Levanians are featured in Somnium (the Dream), a short story written by renowned astronomer Johannes Kepler and released posthumously by his son in 1636. While the ideas on lunar ecology are now obsolete, the astronomical observations from a lunar perspective, as detailed here, are mostly accurate and were considered extremely controversial at the time, since the idea of the Earth orbiting the sun was denied by religious groups. Somnium is often regarded as the first piece of hard science fiction ever written, and its historical significance has been highlighted by enthusiasts of the genre such as Isaac Asimov and Carl Sagan.