Protozoon
The protozoa or protozoa are microscopic, unicellular protist organisms; heterotrophs, phagotrophs, predators or detritivores, sometimes mixotrophs (partially autotrophs); that live in humid environments or directly in aquatic environments, whether salt water or fresh water, and as parasites of other living beings.
Reproduction can be asexual by bipartition and also sexual by isogametes or by conjugation exchanging genetic material. Very diverse taxa with a remote kinship relationship fit into this group, which fit into many different phyla of the kingdom Protista, defining a paraphyletic group, with no value in classification according to cladistic criteria.
The protozoologist Thomas Cavalier-Smith has recovered the Latin version of this name to refer to a eukaryotic kingdom, the kingdom Protozoa, whose limits do not coincide with the traditional concept.
Features
Protozoa are usually 10-50 μm, but can grow up to a few millimeters, and can easily be seen through a microscope. They move with whip-like tails called flagella.
About 30,000 species have been found. Protozoa exist in aqueous environments and in soil, occupying a range of trophic levels.
As predators, they prey on algae, bacteria, and unicellular or filamentous microfungi. Protozoa play a role as herbivores and as consumers in coupling the decomposition process of the food chain. Protozoa also play a vital role in controlling biomass and bacterial population.
They can absorb food through their cell membranes. All protozoa digest their food in compartments called vacuoles.
As components of the micro- and meiofauna, protozoa are an important source of food for microinvertebrates. Thus, the ecological role of protozoa in the transfer of bacterial and algal production to successive trophic levels is important.
Protozoa such as malaria parasites (Plasmodium spp.), trypanosomes, and leishmania are also important as parasites and symbionts of multicellular animals.
Some protozoa have life stages that alternate between proliferative stages (e.g. trophozoites) and inactive cysts. Like cysts, protozoa can survive harsh conditions, such as exposure to extreme temperatures and harmful chemicals, or long periods without access to food, water, or oxygen. Being a cyst enables a parasitic species to survive outside of the host, and allows its transmission from one host to another.
When protozoa are in the form of trophozoites (Greek, trophé = to feed), they feed and grow actively. The process by which the protozoa take their form from the cyst is called encystment, while the process of transformation back into the trophozoite is called echystment.
Protozoa can reproduce by binary fission or multiple fission. Some protozoa reproduce sexually, others asexually, while a third group uses a combination of both processes (eg Coccidia). An individual protozoan is a hermaphrodite. Another name for protozoa is Acrita (R. Owen, 1861).
History
The first to observe protozoa was Leeuwenhoek, who discovered them in 1674 using his own made microscopes. When displayed before the Royal Society they were called animalcules. This discovery was made in a lake in his hometown of Delft, where he observed especially ciliates such as Vorticella and unicellular algae such as Euglena and Volvox .
Name
The name Protozoa (protozoa) was coined by Georg Goldfuss in 1818 to group what he considered to be primordial animals. In 1820 he proposed the class Protozoa within the Animal kingdom, which included the infusoria (Ciliophora), the Lithozoa corals, Phytozoa (unicellular pigmented and photosynthetic algae) and Medusinae (jellyfish and other related). Thus, the concept was different from that of Honigberg (1964), where only ciliates are common to both definitions.
The name is composed of the Greek roots πρώτο (proto), first, and ζώο[ν] (zoo[n]), animal, and reveals that, Originally, the concept expressed the tradition of classifying all forms of life in the animal or plant kingdoms. Thus, the very simple forms that were considered animals were called protozoa, just as microorganisms considered plants were called protophytes.
Unicellularity
In 1845 Carl Theodor Ernst von Siebold used the name to designate a phylum of animals divided into two classes, Infusoria, equivalent to the current phylum Ciliophora (Ciliates), and Rhizopoda, more or less equivalent to those of Honigberg. Von Siebold described them as "unicellular animals." It must be taken into account that in those years he was receiving the consecration of the cell theory. Not everyone, in the following decades, agreed with von Siebold's interpretation, many seeing these organisms as a case of acellular organization. The development of electron microscopy was necessary, in the middle of the XX century, for the homology between the entire protozoan organism and each of the cells on which the microscopic organization of complex organisms is based. It was Dujardin who first, in those years, recognized the unicellular character of the protoplasm of foraminifera, thus finding Von Siebold the authority to define members of the phylum as unicellular.
In 1858, R. Owen elevated Protozoa to the category of a kingdom to separate it from animals and plants.
Protists and Protists
Throughout the rest of the 19th century, approaching the diversity of simple forms continued to be based on the desire to find roots for the two classical kingdoms, animals and plants. The difficulty in achieving this led Hogg, in 1860, to propose a new kingdom for the first time, the Regnum Primigenum or Protista, to group the primitive intermediate beings to plants and animals; one of the examples of it was the green freshwater sponge Spongilla, whose photosynthesis, although real, is attributable to symbiotic green algae. Shortly after, Haeckel proposed the kingdom Protista, "the primordials", for all simple unicellular forms, emphasizing their basal and undifferentiated character, but independent in their evolution from plants and animals. The Protozoa do not exist in this vision of diversity, but in a later revision Haeckel recovered the concepts of protozoa (unicellular animal) and protophyta (unicellular plant), as subkingdoms of the kingdom Protista.
Thus, Haeckel proposed the kingdom Protista which he divided into Protozoa, Protophytes and atypical protists. However, many treatises after Haeckel have continued to classify living beings into animals and plants, in such a way that Protozoa has been considered a phylum within the animal kingdom made up of unicellular organisms.
At the turn of the century, Haeckel's concept, which never claimed to be more than a pragmatic concept, was seen as excessively polyphyletic, with authors, such as Otto Butschli, who rejected the third kingdom, while recovering the notion of Protozoa as a set of animal-like and nucleated organisms.
H. In 1938, F. Copeland addressed global diversity by proposing four kingdoms —Monera, Protista, Plantae and Animalia— drawing to bacteria and cyanobacteria, such as kingdom Monera, from Protista, where Haeckel had left them. For those years Chatton had shown the nucleated character of those organisms. In successive revisions he went on specifying the composition of the Protista kingdom, at the same time that he rescued the name of Hogg (Protista), now with a very different meaning. R. H. Whittaker's nominally derives from this Copeland classification, who, separating the fungi (kingdom Fungi) from Protoctista, finally established a classification into five kingdoms that has lasted a long time. However, Whittaker's definition of kingdoms, who was primarily an ecologist, was based excessively on types of metabolism.
Classical classification
- For a modern classification, see Protista and Protozoa (king)
The best-known traditional classification divides Protozoa into four groups, as reported by Bütschli 1880, Delage & Hérouard 1896, Hartog 1906, Jahn & Jahn 1949 and Mackinnon & Hawes 1961, dominant in zoology texts, treats protozoa as a single phylum divided into four classes based primarily on mode of locomotion. Because all of these forms develop by convergent evolution, the classes are actually complex polyphyletic groups:
- Rhizopods or sarcodi (Rhizopoda, Sarcodina). They are the ameboid protozoos (such as amebas), which travel through pseopodes, that is, forming temporary appendices from their surface and as a cytoplasm projection. The pseopodes are deformations of the cytoplasm and of the plasma membrane that occur in the direction the displacement and that drag behind it the rest of the cell. The pseopodes are also used to capture the food, which encompasses in the interior, in the process called fagocitosis. According to the pseopodes are very thick or very thin, they are of two types: with wobopods (gruesos) such as Lobosea (Amoebozoa) and with various phylopods usually accompanied by an exoeskeleton with microtubules and are such as: radiolars, foraminals, nuclear, heliozoos and others. They can generate diseases known as amebiosis.
- Ciliated (Ciliophora, Ciliata, Infusoria). This is the traditional group that is most identified as a natural group in modern classifications with the category of phyll; although the opalinates that are chromatists also fit into this concept. They appear surrounded by cylios and present a complex internal structure but similar to the scourges, which also relate to cytoskeleton and centrioles. Parametium (gender) Paramecium) is a very popular representative of the group. In addition, the cylios are short and very numerous filaments that with their movement cause cell displacement.
- Flag. or mastigóforos (Mastigophora, Flagellata). They are distinguished by the possession of one or more scourges. The scourges are longer filaments than the cylios whose movement drives the cell. They usually show up in a small number. The naked unicellular forms (without cellular wall), with only one or two flagelos, represent the original form of which all eukaryants derive. That's why so many different protists fit into this concept. Plants, for example, derive ancestrally from biflagelated protozoa that acquired the plates by endosymbiosis with a Cyanobacteria. Several protozoos carry plastos and are therefore autotrophic or mixedtrophos such as dinoflagelados and euglenas. Metamonada has two or multiple scourges, are anaerobic and mostly symbiont or animal parasites. Among the uniflagelados are the coanoflagelados, ancestral of the animals and the quitrides, ancestral of the fungi.
- Swords (Sporozoa). Parasites with a sporulation phase (multi-division) and without greater mobility. There are several different groups without greater relationship and they are not all protists, but there are also animals and fungi. The best known example is plasmodium (gender) Plasmodium), cause of malaria and that belongs to the group of apicomplejos, a better known group that usually reserves for itself the name of Sporozoa. The Haplosporidios are considered part of Cercozoa. These two groups have been reunited for a long time under the name of Cnidosporidio. The Ichthiosporea are a more recent group and are within Choanozoa. Microspordiums are now attached to the kingdom Fungi and Mixosporidios or Mixozoos to the Kingdom Animal.
On the other hand, Honigberg & cabbage. (1964), divided Protozoa into four subphyla: Sarcomastigophora, Sporozoa, Cilophora, and Cnidospora; the latter that grouped mixozoans and microsporidia.