Tree of life.

Based on rRNA gene sequences, organisms are divided into 3 domains: Bacteria, Archaea, and Eukarya.

Eukarya and Archaea share a common ancestor, and are more closely related to each other than to Bacteria.

Archaea and Bacteria are "prokaryotes" that lack organelles such as a nucleus.

The lack of organelles is not a shared derived character, thus "prokaryotes" do not constitute a monophyletic clade.