Archaea (Archaeon ): Single-celled microorganisms without nuclei and with membranes different from all other organisms. Once thought to be bacteria.
Unicellular organism
-A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Unicellular organisms fall into two general categories: prokaryotic organisms and eukaryotic organisms.
