The arrow below shows where protozoa lie on the phylogenetic tree. They are eukaryotes, but they are still closely related to archaea and bacteria.
Protozoans are single-celled eukaryotes which have a membrane bound nucleus. There are 4 main types of protozoa: ameba, flagellates, ciliates, and sporozoa. The difference between each of these lies in their method of motility. They generally are found in moist environments, but they are very diverse and difference species have different niches.