Thushol

The Thushol are a sapient species of shapeshifters from the planet Mars. In addition to shapeshifting, they use their powerful telepathy to probe the minds of other creatures and acquire knowledge that helps them to infiltrate other species' societies.

Biology
The Thushol are incredibly adaptable creatures which can alter their cellular protoplasm to mimic any kind of organic matter, assuming animal or vegetable forms at will. As such, they can survive on any kind of environment by assuming a form that's suitable (e.g. a fish in the sea, a cactus on the desert, etc.). Their natural form is winged, resembling a bat-like creature with menacing eyes.

In addition to their shapeshifting abilities, Thushol are formidable telepaths which can passively probe the minds of other creatures and learn how to imitate their behaviour. Even other telepaths, such as the Martian Centaurs, are unable to identify a Thushol while it's disguised as another being.

Originally, the Thushol reproduced slowly, but eventually learned to reproduce quickly by fragmentation, by which a single Thushol can split into multiple smaller ones.

Appearances

 * "The Brain Stealers of Mars", by John W. Campbell (1936)
 * "The Double Minds", by John W. Campbell (1937)
 * "The Immortality Seekers", by John W. Campbell (1937)
 * "The Tenth World", by John W. Campbell (1937)