The Pyroplancton is a kind of protozoan microorganism which is the unique kind of life in the entire Universe if you exclude Earth. Its name means: Pyros (Greek fire) refers to its capacity to resist and to enjoy very hot environments like extraterrestial volcanoes and thermas. Many of them are able to live in the surface of really hot stars. The placton word refers to its alga-like way of life, extracting its energy from the light.
Some time ago, the first extrasolar ship fell in a extrasolar asteroid named Asteros. They survived the hit, but two spacemen (spaceman Spiff and spacelady Diana) had many lacerations. They both were invaded by Esterium, a unique kind of microorganism from Asteria, and they fell unconscious. The other spacemen tried to save them, and they were about to inject them a medicine but suddenly the strange atmosphere entered into the ship and everyone died except Spiff and Diana. After some time Spiff and Diana wook up, and they discovered they were immune to the atmosphere of Asteros. Its lacerations were cured, as a miracle, and they analyze their own blood. They discovered the Esterium had become part of them, in a symbiosis in which Esterium gave them the adaptation to the planet. However their unions was imperfect, and after ten years Spiff and Diana died. However, they had mated and they children were really different beings, totally adapted to the planet, with a total mix of human DNA and Esterium UNA (Unknown Nucleic Acid). Their children reproduced, and they founded an advanced civilization. The mian differences between humans and humans of Asteros are: dark red skin, red eyes, a pair of light-absorbing antennas and reproduction through eggs.
Since that time, the human colonizers of each different extra-solar planet inject themselves local pyroplancton to become adapted to the planet to colonize.