Space Amoeba (Star Trek)

The "Space Amoeba" is a huge unicellular lifeform which dwells in space vacuum, surrounded by a negative energy field.

Biology
The giant amorphous creature is thousands of miles large and seems to be made out of some unusual forms of matter and/or antimatter. It is known to exert attraction over spaceships and interfere with their workings, and stays alive by consuming entire planets, asteroids and ships. The negative energy it generates causes disease and exhaustion in humanoid lifeforms and creates a zone of darkness, annihilating regular energy in a similar manner to which antimatter annihilates matter. Within the negative field strange things can happen, for example: activating backward thrust could cause the ship to go forward instead, though the exact mechanism behind this remains unexplained. Although vast, this single-celled organism is biologically simple and reproduces itself by means of binary fission.

History
A large space amoeba originated from some unknown parts of the universe invades the Milky Way galaxy in the year of 2268, causing the destruction of an inhabited planet and a Vulcan starship. Upon meeting it, the crew of the starship USS Enterprise compares the amoeba to a germ infecting the galaxy and preparing to multiply. Foreseeing the enormous threat that it represented, they used an antimatter charge to destroy the invader.

Appearances

 * Star Trek, s02e18, "The Immunity Syndrome" (1968)