Kingdom Protista: what is it, characteristics, classification and examples

We begin by explaining what the Protista kingdom is , before going into details about its characteristics, classification and other aspects. The Protista or protoctist kingdom appeared as the third of the five great kingdoms of living beings in nature ( Animalia or animal kingdom, Plantae or vegetable kingdom, Protista or Protista kingdom, Fungi kingdom or fungi kingdom. and kingdom Monera or monera). But what exactly does the Protista kingdom include ? This kingdom includes all those unicellular and multicellular eukaryotic organisms with intermediate anatomical and functional characteristics between plants and animals..

Going unnoticed and being great unknown of the incredible biodiversity that nature hides, protists fill many corners of the planet with micro and macroscopic life , from fresh and salt water ecosystems, as well as on humid land and even as animal parasites. In the next sections we will learn more about these mysterious and fascinating organisms, the protists .

Among the main characteristics of the Protistas kingdom are:

• They are eukaryotic organisms (with a nucleus delimited by a membrane), lacking differentiated vegetative tissues, except in those structures destined for the reproduction process.
• The size of the protists is highly variable, from microscopic unicellular forms to multicellular organisms several meters long.
• They are found in a wide variety of places: soil, fresh water, ocean floor, decomposing organic matter, etc.
• In the kingdom of the protists all possible nutrition models are exhibited: autotrophic (phototrophic) and heterotrophic , through phagotrophic, saprobiotic or parasitic strategies.
• They present a great variety of types of locomotion, by means of flagella, cilia and pseudopods; although there are also numerous species that lack mobility. Many organisms are free-living, while others have symbiotic relationships (mutualistic, commensal, or parasite ).
• Some species of the Protista kingdom have developed the amazing ability to form, during their life cycles, resistance structures (called cysts) in periods of unfavorable conditions such as lack of water and food, thus surviving in a dormant state (stopping their metabolic functions), until more favorable conditions for their reproduction and survival arrive. In addition, they are capable of forming spores in those stages of the life cycle that guarantee their multiplication and propagation.
• The reproduction protists is governed by different reproductive such strategies as asexual reproduction through mitosis, bipartition, budding or division multiple; as well as sexual reproductive activity with mitotic and meiotic processes. Learn more about these reproductive processes with this other article on the Difference between mitosis and meiosis .

The complex and diverse characteristics of protists or protoctists make their classification one of the most difficult and convoluted in the evolution of living beings. Many have been the scientists who throughout history have tried to determine a classification for the Protista kingdom as accurate as possible. At present, the different protists are classified into the following supergroups:

• Amebozoa: amoebas, slime molds and myxomycetes.
• Archaeplastida: red algae (Rhodophyta)
• Excavata: flagellated organisms of the Euglenozoa and Percolozoa groups.
• Stramenopiles: brown algae, diatoms, chrysophyceae and xanthophyceae.
• Alveolata: ciliated organisms, dinoflagellates and apicomplexes.
• Rhizaria: foraminiferous, radiolarian and cercozoan microorganisms.
• Opisthokonta: metazoans with differentiated tissues, fungi, choanoflagellates and Mesomycetozoa.

In the next section we will see some examples of protist species to better understand what name and appearance these mysterious living beings have.

After knowing all this, we still wonder what are the organisms that belong to the protist kingdom , so here we summarize that some of the main genera and most representative species to give examples of the Protista kingdom or examples of the protoctists are:

• Laminaria digitata (large laminar brown algae, reaches two meters in length)
• Genus Sargassum (“Sargasso”, brown macroalgae several meters long)
• Genus Chlamydomonas (freshwater unicellular green algae)
• Genus Ulva (“sea lettuce” alga)
• Trypanosoma cruzi (produces chagas disease)
• Entamoeba histolytica (intestinal parasite)
• Balantidium coli (produces Balantidian dysentery)
• Paramecium caudatum (free-living protozoan)
• Plasmodium vivax ( causes malaria)
• Giardia lamblia (intestinal parasite)
• Trichomonas vaginalis (vaginal parasite)

Here you can see images of the kingdom Protista (these are some of the species in this list of examples of protists )

The diverse kingdom of the protists had, from its origin, a great importance within the world of scientific taxonomy and biology, among other branches of science. Although at present, articles and studies mention it as the Protista kingdom (“primordial”), the scientist Margulis tried to give them the importance they deserved by choosing the name of “Protoctista kingdom” (from the Greek “first creatures” ), highlighting thus its relevance in the knowledge of the evolution of living beings .

As we have been discovering in the previous sections of this article, protists play a really important role in the functioning of different ecosystems, as well as in the world of medicine, since many of these organisms are the cause of some of the most dangerous diseases that affect humans.