Answer:
Prokaryotes.
Step-by-step explanation:
Prokaryotes are the unicellular organism that lacks the membrane bound organelle. A well defined nucleus is absent in the prokaryotic organism. Three domain of life are archaea, bacteria and prokarya.
Prokaryotes include the domains archaea and bacteria. Both these domains contain flagella like structure for their locomotion. The organisms are unable to be seen with naked eye and all organism are microscopic organism.
Thus, the correct answer is prokaryotes.