Archaea

Archaea are microorganisms often counting one single cell. They look like bacteria, but they are not close relative to them : they are one of the three great groups (called domains) of living beings (with the two others being bacteria and eukaryotes).

Archaea use to live in very hostile environments: hot water springs, acid lakes, polar ices. Some archaea were among the first living beings on Earth, and their descendants are still alive nowadays.