These aliens are a mysterious and unknown species reported to inhabit a small planet at the edge of the Milky Way Galaxy, orbiting a giant red sun. Although the planet has five moons, these are all negligibly small; unfit to cast light upon the pitch-black nights of this otherwise barren world.
These creatures have never been seen directly, and thus cannot be described in therms of physical appearance. Likewise, their intelligence level is also completely unknown. What is known is that they're strictly nocturnal beings, which live in tunnels to avoid the scorching red sun that emits deadly radiation during the day.
At night, they move around silently over the rocks, except for an omnipresent chitinous clicking sound, similar to that of a crab's pincers; and use the rocky walls of their volcanic tunnels as whetstones to sharpen their claws.
Since the planet seems to have no vegetation or other forms of life, it is speculated that these aliens may have an autotrophic metabolism, although their exact source of energy is not known, and it's heavily implied that they prey upon other creatures opportunistically.
- "A Walk in the Dark", by Arthur C. Clarke (1950)