They are believed to be a part of the microbial world as they are unicellular and microscopic. The group of organisms known as 'protozoa' are defined by a few of their shared characteristics. They live in a wide variety of moist habitats including fresh water, marine environments and the soil. Protozoa are divided into four major groups based on the structure and the part involved in the locomotion: 1. It was first coined in the 1800s. They come in many different shapes and sizes ranging from an Amoeba which can change its shape to Paramecium with its fixed shape and complex structure. See more. Furthermore, the scientist has described more than 50 thousand species of Protozoa. Protozoa is a single cell animal that we can find in every possible habitat on earth. Protozoa [pro″to-zo´ah] a subkingdom (formerly a phylum) comprising the unicellular eukaryotic organisms; most are free-living, but some lead commensalistic, mutualistic, or parasitic existences. Protozoa is a phylum having unicellular heterotrophs. In some newer schemes, however, most algae are classified in the kingdoms Plantae and Chromista , and in such cases the remaining forms may be classified as a kingdom Protozoa. It comes under Kingdom Protista. There is a great deal to know about their classification, characteristics and more. It is a loose assemblage of different groups of unicellular organisms and they do not belong to a monophyletic Unease, probably shares a member of polyphyletic lineases. home >> biology >> definition They belong among the eukaryotes , and are often grouped in the kingdom Protista together with the plant-like algae . They have flagella for locomotion Learn more about it. Protozoa definition, a major grouping or superphylum of the kingdom Protista, comprising the protozoans. Definition: Unicellular or acellular, eukaryotic and commonly motile heterotrophic organisms are called Protozoa. Moreover, they are herbivores, carnivores, and omnivores. Protozoa. Protozoa are single-celled organisms without cell walls. Before then, the microscopic protozoa, defined by their organelles, were unable to be fully appreciated. Mastigophora or Flagellates: They are parasites or free-living. Protozoa are non-phototrophic, unicellular, eukaryotic microorganisms with no … Protozoan, organism, usually single-celled and heterotrophic (using organic carbon as a source of energy), belonging to any of the major lineages of protists and, like most protists, typically microscopic. Protozoa (meaning "first animals") are heterotrophic, single-celled or colonial eukaryotes. Protozoa Classification and Examples. Protozoa are single celled organisms. The word protozoa comes from the word protos, which was Greek for "first," and zoia which meant "animal." All protozoans are eukaryotes and therefore possess a “true,” or membrane-bound, nucleus. Protozoa.