Question

why Arachaebacteria is called living fossil?

Answer 1

The Archaea comprise a group of single-celled microorganisms that, like bacteria, are prokaryotes that have no cell nucleus or any other organelles within their cells. Consequently, they were once considered to be an unusual group of bacteria and named archaebacteria.

Answer 2

Archaebacteria are single celled organisms with no nucleus and other organelles.
Living fossils are species which exist. Archae have studies to be originated around 4 billions ago.They have escaped all the extintion events due to simplest structure and growth in adverse conditions.Therefore they are known as living fossils.

Hope it helps u.....