Any prokaryotic organism (e.g. bacteria).
Yes, a single-cell organism is an organism, it contains a nucleus.
Red blood cell
Organisms such as bacterias that has no true nucleus.
An animal cell
paramecium
Eukaryotic cell is a multicellular, or a single-celled organism, that has a distinct membrane-bound nucleus.
archaeabacteria and eubacteria both are single cell organisms without nucleus
An prokaryotic cell organism like bacteria answered by m.buallay
Bacteria are most commonly prokaryotes and have no membrane-bound organelles which includes the nucleus.
help
I assume you meant single "celled" organism. It is an organism (life form) that consists of only a sigle cell as opposed to most all other lifeforms on earth which are comprised of many (billions) of cells.
Eukaryote