<P> All protozoans reproduce asexually by binary fission or multiple fission . Many protozoan species exchange genetic material by sexual means (typically, through conjugation); however, sexuality is generally decoupled from the process of reproduction, and does not immediately result in increased population . </P> <P> Although meiotic sex is widespread among present day eukaryotes, it has, until recently, been unclear whether or not eukaryotes were sexual early in their evolution . Due to recent advances in gene detection and other techniques, evidence has been found for some form of meiotic sex in an increasing number of protozoans of ancient lineage that diverged early in eukaryotic evolution . (See eukaryote reproduction .) Thus, such findings suggest that meiotic sex arose early in eukaryotic evolution . Examples of protozoan meiotic sexuality are described in the articles Amoebozoa, Giardia lamblia, Leishmania, Plasmodium falciparum biology, Paramecium, Toxoplasma gondii, Trichomonas vaginalis and Trypanosoma brucei . </P> <P> Historically, the Protozoa were classified as "unicellular animals", as distinct from the Protophyta, single - celled photosynthetic organisms (algae) which were considered primitive plants . Both groups were commonly given the rank of phylum, under the kingdom Protista . In older systems of classification, the phylum Protozoa was commonly divided into several sub-groups, reflecting the means of locomotion: Classification schemes differed, but throughout much of the 20th century the major groups of Protozoa included: </P> <Ul> <Li> Flagellates, or Mastigophora (motile cells equipped with whiplike organelles of locomotion, e.g., Giardia lamblia) </Li> <Li> Amoebae or Sarcodina (cells that move by extending pseudopodia or lamellipodia, e.g., Entamoeba histolytica) </Li> <Li> Sporozoans, or Sporozoa (parasitic, spore - producing cells, whose adult form lacks organs of motility, e.g., Plasmodium knowlesi) <Ul> <Li> Apicomplexa (now in Alveolata) </Li> <Li> Microsporidia (now in Fungi) </Li> <Li> Ascetosporea (now in Rhizaria) </Li> <Li> Myxosporidia (now in Cnidaria) </Li> </Ul> </Li> <Li> Ciliates, or Ciliophora (cells equipped with large numbers of short hairlike organs of locomotion, e.g., Balantidium coli </Li> </Ul>

Protozoan classification used to be based on their means of