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Protozoa (sg.: protozoan or protozoon; alternative plural: protozoans) are a polyphyletic group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic debris.
The characteristics of phylum sarcomastigophora are : (1) Nucleus is of one type except in the stages of certain foraminifera. (2) Locomotory organ either pseudopodia or flagella or both. (3) Reproduction asexual, but when sexually it is essentially by syngamy. Example : Amoeba, Euglena etc.
This article largely follows the efforts of the scientific community and the International Society of Protistologists to revise the taxonomy of protists in a manner that reflects their phylogeny and evolution, striving away from the use of historical paraphyletic taxa and relying exclusively on clades as the basis of the classification.
Its field of study therefore overlaps with the more traditional disciplines of phycology, mycology, and protozoology, just as protists embrace mostly unicellular organisms described as algae, some organisms regarded previously as primitive fungi, and protozoa ("animal" motile protists lacking chloroplasts).
The Apicomplexa comprise the bulk of what used to be called the Sporozoa, a group of parasitic protozoans, in general without flagella, cilia, or pseudopods. Most of the Apicomplexa are motile, however, with a gliding mechanism [ 5 ] that uses adhesions and small static myosin motors. [ 6 ]
The International Society of Protistologists, the recognised body for taxonomy of protozoa, recommended in 2012 that the term Unikont be changed to Amorphea because the name "Unikont" is based on a hypothesized synapomorphy that the ISOP authors and other scientists later rejected. [1] [5] It includes amoebozoa, opisthokonts, [6] [7] and ...
The parasitologist F. E. G. Cox noted that "Humans are hosts to nearly 300 species of parasitic worms and over 70 species of protozoa, some derived from our primate ancestors and some acquired from the animals we have domesticated or come in contact with during our relatively short history on Earth". [3]
Microscopic organisms were increasingly constrained in the plant/animal dichotomy. In 1858, the palaeontolgist Richard Owen was the first to define Protozoa as a separate kingdom of eukaryotic organisms, with "nucleated cells" and the "common organic characters" of plants and animals, although he also included sponges within protozoa. [27]