The correct answer is Protozoans.
Protozoans are best described as uni-celled eukaryotic organisms, both free-residing or parasitic, which feed on organic matter together with different microorganisms or organic tissues and particles. back then, the protozoa have been seemed as "one-celled animals," because they regularly possess animal-like behaviors, together with motility and predation, and lack a mobile wall, as discovered in plant life and plenty of algae.