Subkingdom (biology)
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In
biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary i ...
, a kingdom is the second highest
taxonomic rank In biological classification, taxonomic rank is the relative level of a group of organisms (a taxon) in an ancestral or hereditary hierarchy. A common system consists of species, genus, family, order, class, phylum, kingdom, domain. While ...
, just below domain. Kingdoms are divided into smaller groups called phyla. Traditionally, some textbooks from the United States and Canada used a system of six kingdoms (
Animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
ia,
Plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclu ...
ae,
Fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
,
Protist A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the exc ...
a, Archaea/Archaebacteria, and
Bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
/Eubacteria) while textbooks in Great Britain, India, Greece, Brazil and other countries use five kingdoms only (Animalia, Plantae, Fungi, Protista and
Monera Monera (/məˈnɪərə/) (Greek - μονήρης (monḗrēs), "single", "solitary") is a biological kingdom that is made up of prokaryotes. As such, it is composed of single-celled organisms that lack a nucleus. The taxon Monera was first p ...
). Some recent classifications based on modern
cladistics Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups (" clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived cha ...
have explicitly abandoned the term ''kingdom'', noting that some traditional kingdoms are not monophyletic, meaning that they do not consist of all the descendants of a common ancestor. The terms ''
flora Flora is all the plant life present in a particular region or time, generally the naturally occurring (indigenous (ecology), indigenous) native plant, native plants. Sometimes bacteria and fungi are also referred to as flora, as in the terms '' ...
'' (for plants), ''
fauna Fauna is all of the animal life present in a particular region or time. The corresponding term for plants is ''flora'', and for fungi, it is ''funga''. Flora, fauna, funga and other forms of life are collectively referred to as ''Biota (ecology ...
'' (for animals), and, in the 21st century, '' funga'' (for fungi) are also used for life present in a particular region or time.


Definition and associated terms

When
Carl Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his Nobility#Ennoblement, ennoblement in 1761 as Carl von Linné#Blunt, Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalise ...
introduced the rank-based system of
nomenclature Nomenclature (, ) is a system of names or terms, or the rules for forming these terms in a particular field of arts or sciences. The principles of naming vary from the relatively informal conventions of everyday speech to the internationally ag ...
into biology in 1735, the highest rank was given the name "kingdom" and was followed by four other main or principal ranks:
class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differentl ...
, order,
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
and
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
. Later two further main ranks were introduced, making the sequence kingdom, phylum or division,
class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differentl ...
, order,
family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
,
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
and
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
. In 1990, the rank of domain was introduced above kingdom. Prefixes can be added so ''subkingdom'' (''subregnum'') and ''infrakingdom'' (also known as ''infraregnum'') are the two ranks immediately below kingdom. Superkingdom may be considered as an equivalent of domain or empire or as an independent rank between kingdom and domain or subdomain. In some classification systems the additional rank ''branch'' (Latin: ''ramus'') can be inserted between subkingdom and infrakingdom, e.g., Protostomia and
Deuterostomia Deuterostomia (; in Greek) are animals typically characterized by their anus forming before their mouth during embryonic development. The group's sister clade is Protostomia, animals whose digestive tract development is more varied. Some ex ...
in the classification of Cavalier-Smith.


History


Two kingdoms of life

The classification of living things into animals and plants is an ancient one.
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of ph ...
(384–322 BC) classified animal species in his ''
History of Animals ''History of Animals'' ( grc-gre, Τῶν περὶ τὰ ζῷα ἱστοριῶν, ''Ton peri ta zoia historion'', "Inquiries on Animals"; la, Historia Animalium, "History of Animals") is one of the major texts on biology by the ancient Gr ...
'', while his pupil
Theophrastus Theophrastus (; grc-gre, Θεόφραστος ; c. 371c. 287 BC), a Greek philosopher and the successor to Aristotle in the Peripatetic school. He was a native of Eresos in Lesbos.Gavin Hardy and Laurence Totelin, ''Ancient Botany'', Routle ...
(–) wrote a parallel work, the '' Historia Plantarum'', on plants.
Carl Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his Nobility#Ennoblement, ennoblement in 1761 as Carl von Linné#Blunt, Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalise ...
(1707–1778) laid the foundations for modern
biological nomenclature Nomenclature codes or codes of nomenclature are the various rulebooks that govern biological taxonomic nomenclature, each in their own broad field of organisms. To an end-user who only deals with names of species, with some awareness that species ...
, now regulated by the
Nomenclature Codes Nomenclature codes or codes of nomenclature are the various rulebooks that govern biological taxonomic nomenclature, each in their own broad field of organisms. To an end-user who only deals with names of species, with some awareness that specie ...
, in 1735. He distinguished two kingdoms of living things: ''Regnum Animale'' ('
animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
kingdom') and ''Regnum Vegetabile'' ('vegetable kingdom', for
plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclu ...
s). Linnaeus also included
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...
s in his
classification system Classification is a process related to categorization, the process in which ideas and objects are recognized, differentiated and understood. Classification is the grouping of related facts into classes. It may also refer to: Business, organizat ...
, placing them in a third kingdom, '' Regnum Lapideum''.


Three kingdoms of life

In 1674, Antonie van Leeuwenhoek, often called the "father of microscopy", sent the
Royal Society The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, re ...
of London a copy of his first observations of microscopic single-celled organisms. Until then, the existence of such microscopic organisms was entirely unknown. Despite this, Linnaeus did not include any microscopic creatures in his original taxonomy. At first, microscopic organisms were classified within the animal and plant kingdoms. However, by the mid–19th century, it had become clear to many that "the existing dichotomy of the plant and animal kingdoms
ad become Advertising is the practice and techniques employed to bring attention to a product or service. Advertising aims to put a product or service in the spotlight in hopes of drawing it attention from consumers. It is typically used to promote a ...
rapidly blurred at its boundaries and outmoded". In 1860 John Hogg proposed the ''Protoctista'', a third kingdom of life composed of "all the lower creatures, or the primary organic beings"; he retained Regnum Lapideum as a fourth kingdom of minerals. In 1866, Ernst Haeckel also proposed a third kingdom of life, the ''
Protista A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the exc ...
'', for "neutral organisms" or "the kingdom of primitive forms", which were neither animal nor plant; he did not include the Regnum Lapideum in his scheme. Haeckel revised the content of this kingdom a number of times before settling on a division based on whether organisms were unicellular (Protista) or multicellular (animals and plants).


Four kingdoms

The development of microscopy revealed important distinctions between those organisms whose cells do not have a distinct
nucleus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom * Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucl ...
(
prokaryote A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Conne ...
s) and organisms whose cells do have a distinct nucleus ( eukaryotes). In 1937
Édouard Chatton Édouard Chatton (; 11 October 1883 – 23 April 1947) was a French biologist who first characterized the distinction between the prokaryotic and eukaryotic cellular types. Chatton coined the terms and published them first in his 1937 paper ' ...
introduced the terms "prokaryote" and "eukaryote" to differentiate these organisms. In 1938, Herbert F. Copeland proposed a four-kingdom classification by creating the novel Kingdom
Monera Monera (/məˈnɪərə/) (Greek - μονήρης (monḗrēs), "single", "solitary") is a biological kingdom that is made up of prokaryotes. As such, it is composed of single-celled organisms that lack a nucleus. The taxon Monera was first p ...
of prokaryotic organisms; as a revised phylum Monera of the Protista, it included organisms now classified as
Bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
and Archaea. Ernst Haeckel, in his 1904 book ''The Wonders of Life'', had placed the blue-green algae (or Phycochromacea) in Monera; this would gradually gain acceptance, and the blue-green algae would become classified as bacteria in the phylum Cyanobacteria. In the 1960s,
Roger Stanier Roger Yate Stanier (22 October 1916 – 29 January 1982) was a Canadian microbiologist who was influential in the development of modern microbiology. As a member of the Delft School and former student of C. B. van Niel, he made important contribu ...
and
C. B. van Niel Cornelis Bernardus van Niel (also known as Kees van Niel) (November 4, 1897 – March 10, 1985) was a Dutch-American microbiologist. He introduced the study of general microbiology to the United States and made key discoveries explaining t ...
promoted and popularized Édouard Chatton's earlier work, particularly in their paper of 1962, "The Concept of a Bacterium"; this created, for the first time, a rank above kingdom—a ''superkingdom'' or ''empire''—with the
two-empire system The two-empire system (two-superkingdom system) was the top-level biological classification system in general use before the establishment of the three-domain system. It classified cellular life into Prokaryota and Eukaryota as either "empires" or ...
of prokaryotes and eukaryotes. The two-empire system would later be expanded to the
three-domain system The three-domain system is a biological classification introduced by Carl Woese, Otto Kandler, and Mark Wheelis in 1990 that divides cellular life forms into three domains, namely Archaea, Bacteria, and Eukaryota or Eukarya. The key difference ...
of Archaea, Bacteria, and Eukaryota.


Five kingdoms

The differences between
fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
and other organisms regarded as plants had long been recognised by some; Haeckel had moved the fungi out of Plantae into Protista after his original classification, but was largely ignored in this separation by scientists of his time. Robert Whittaker recognized an additional kingdom for the
Fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
. The resulting five-kingdom system, proposed in 1969 by Whittaker, has become a popular standard and with some refinement is still used in many works and forms the basis for new multi-kingdom systems. It is based mainly upon differences in
nutrition Nutrition is the biochemical and physiological process by which an organism uses food to support its life. It provides organisms with nutrients, which can be metabolized to create energy and chemical structures. Failure to obtain sufficient ...
; his Plantae were mostly multicellular
autotroph An autotroph or primary producer is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) using carbon from simple substances such as carbon dioxide,Morris, J. et al. (2019). "Biology: How Life Wo ...
s, his Animalia multicellular
heterotroph A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...
s, and his Fungi multicellular
saprotroph Saprotrophic nutrition or lysotrophic nutrition is a process of chemoheterotrophic extracellular digestion involved in the processing of decayed (dead or waste) organic matter. It occurs in saprotrophs, and is most often associated with fungi ( ...
s. The remaining two kingdoms, Protista and Monera, included unicellular and simple cellular colonies. The five kingdom system may be combined with the two empire system. In the Whittaker system, Plantae included some algae. In other systems, such as
Lynn Margulis Lynn Margulis (born Lynn Petra Alexander; March 5, 1938 – November 22, 2011) was an American evolutionary biologist, and was the primary modern proponent for the significance of symbiosis in evolution. Historian Jan Sapp has said that "Lynn Ma ...
's system of five kingdoms, the plants included just the land plants (
Embryophyta The Embryophyta (), or land plants, are the most familiar group of green plants that comprise vegetation on Earth. Embryophytes () have a common ancestor with green algae, having emerged within the Phragmoplastophyta clade of green algae as siste ...
), and Protoctista has a broader definition. Following publication of Whittaker's system, the five-kingdom model began to be commonly used in high school biology textbooks. But despite the development from two kingdoms to five among most scientists, some authors as late as 1975 continued to employ a traditional two-kingdom system of animals and plants, dividing the plant kingdom into subkingdoms Prokaryota (bacteria and cyanobacteria), Mycota (fungi and supposed relatives), and Chlorota (algae and land plants). {, role="presentation" class="wikitable mw-collapsible" , + {{nowrap, Whittaker's five kingdom system (1969) , -style="font-size: 87%;vertical-align: top;background: white" , , Kingdom
Monera Monera (/məˈnɪərə/) (Greek - μονήρης (monḗrēs), "single", "solitary") is a biological kingdom that is made up of prokaryotes. As such, it is composed of single-celled organisms that lack a nucleus. The taxon Monera was first p ...
*Branch Myxomonera **Phylum
Cyanophyta Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...
**Phylum Myxobacteriae *Branch Mastigomonera **Phylum Eubacteriae **Phylum Actinomycota **Phylum Spirochaetae , , Kingdom
Protista A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the exc ...
*Phylum
Euglenophyta Euglenids (euglenoids, or euglenophytes, formally Euglenida/Euglenoida, ICZN, or Euglenophyceae, ICBN) are one of the best-known groups of flagellates, which are excavate eukaryotes of the phylum Euglenophyta and their cell structure is typic ...
*Phylum Chrysophyta *Phylum Pyrrophyta *Phylum Hyphochytridiomycota *Phylum
Plasmodiophoromycota The plasmodiophores (also known as plasmophorids or plasmodiophorids) are a group of obligate endoparasitic protists belonging to the subphylum Endomyxa in Cercozoa. Taxonomically, they are united under a single family Plasmodiophoridae, order ...
*Phylum
Sporozoa The Apicomplexa (also called Apicomplexia) are a large phylum of parasitic alveolates. Most of them possess a unique form of organelle that comprises a type of non-photosynthetic plastid called an apicoplast, and an apical complex structure. The ...
*Phylum Cnidosporidia *Phylum
Zoomastigina A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes and their ...
*Phylum Sarcodina *Phylum
Ciliophora The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to eukaryotic flagella, but are in general shorter and present in much larger numbers, with a different ...
, , Kingdom
Plantae Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclude ...
*Subkingdom Rhodophycophyta **Phylum Rhodophyta *Subkingdom Phaeophycophyta **Phylum Phaeophyta *Subkingdom Euchlorophyta **Branch Chlorophycophyta ***Phylum
Chlorophyta Chlorophyta or Prasinophyta is a taxon of green algae informally called chlorophytes. The name is used in two very different senses, so care is needed to determine the use by a particular author. In older classification systems, it refers to a ...
***Phylum
Charophyta Charophyta () is a group of freshwater green algae, called charophytes (), sometimes treated as a division, yet also as a superdivision or an unranked clade. The terrestrial plants, the Embryophyta emerged within Charophyta, possibly from terre ...
**Branch Metaphyta ***Phylum Bryophyta ***Phylum
Tracheophyta Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They a ...
, , Kingdom
Fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
*Subkingdom Gymnomycota **Phylum Myxomycota **Phylum
Acrasiomycota The family Acrasidae (ICZN, or Acrasiomycota, ICBN) is a family of slime molds which belongs to the excavate group Percolozoa. The name element - comes from the Greek ''akrasia'', meaning "acting against one's judgement". This group consists ...
**Phylum
Labyrinthulomycota The Labyrinthulomycetes (ICBN) or Labyrinthulea ( ICZN) are a class of protists that produce a network of filaments or tubes, which serve as tracks for the cells to glide along and absorb nutrients for them. The two main groups are the laby ...
*Subkingdom Dimastigomycota **Phylum
Oomycota Oomycota forms a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms, called oomycetes (). They are filamentous and heterotrophic, and can reproduce both sexually and asexually. Sexual reproduction of an oospore is the result ...
*Subkingdom
Eumycota A fungus (plural, : fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified ...
**Branch Opisthomastigomycota ***Phylum
Chytridiomycota Chytridiomycota are a division of zoosporic organisms in the kingdom Fungi, informally known as chytrids. The name is derived from the Ancient Greek ('), meaning "little pot", describing the structure containing unreleased zoöspores. Chytri ...
**Branch Amastigomycota ***Phylum
Zygomycota Zygomycota, or zygote fungi, is a former division or phylum of the kingdom Fungi. The members are now part of two phyla: the Mucoromycota and Zoopagomycota. Approximately 1060 species are known. They are mostly terrestrial in habitat, living ...
***Phylum Ascomycota ***Phylum Basidiomycota , , Kingdom Animalia *Subkingdom Agnotozoa **Phylum
Mesozoa The Mesozoa are minuscule, worm-like parasites of marine invertebrates. Generally, these tiny, elusive creatures consist of a somatoderm (outer layer) of ciliated cells surrounding one or more reproductive cells. A recent study recovered Mesoz ...
*Subkingdom Parazoa **Phylum Porifera **Phylum
Archaeocyatha Archaeocyatha (or archaeocyathids 'ancient cups') is a taxon of extinct, sessile, reef-building marine sponges that lived in warm tropical and subtropical waters during the Cambrian Period. It is believed that the centre of the Archaeocyatha or ...
{{extinct *Subkingdom Eumetazoa **Branch
Radiata Radiata or Radiates is a historical taxonomic rank that was used to classify animals with radially symmetric body plans. The term Radiata is no longer accepted, as it united several different groupings of animals that do not form a monophyletic ...
***Phylum
Cnidaria Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter. Their distinguishing feature is cnidocytes, specialized cells that ...
***Phylum
Ctenophora Ctenophora (; ctenophore ; ) comprise a phylum of marine invertebrates, commonly known as comb jellies, that inhabit sea waters worldwide. They are notable for the groups of cilia they use for swimming (commonly referred to as "combs"), and ...
**Branch Bilateria ***Grade Acoelomata ****Phylum
Platyhelminthes The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") are a phylum of relatively simple bilaterian, unsegme ...
****Phylum
Nemertea Nemertea is a phylum of animals also known as ribbon worms or proboscis worms, consisting of 1300 known species. Most ribbon worms are very slim, usually only a few millimeters wide, although a few have relatively short but wide bodies. Many h ...
or Rhynchocoela ***Grade
Pseudocoelomata The Aschelminthes (also known as Aeschelminthes, Nemathelminthes, Nematodes), closely associated with the Platyhelminthes, are an obsolete phylum of pseudocoelomate and other similar animals that are no longer considered closely related and have be ...
****Phylum
Acanthocephala Acanthocephala (Greek , ', thorn + , ', head) is a phylum of parasitic worms known as acanthocephalans, thorny-headed worms, or spiny-headed worms, characterized by the presence of an eversible proboscis, armed with spines, which it uses to p ...
****Phylum Aschelminthes ****Phylum
Entoprocta Entoprocta (), or Kamptozoa , is a phylum of mostly sessile aquatic animals, ranging from long. Mature individuals are goblet-shaped, on relatively long stalks. They have a "crown" of solid tentacles whose cilia generate water currents that ...
or Kamptozoa ***Grade
Coelomata The coelom (or celom) is the main body cavity in most animals and is positioned inside the Body (biology), body to surround and contain the digestive tract and other Organ (biology), organs. In some animals, it is lined with mesothelium. In other ...
****Subgrade Schizocoela *****Phylum
Bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies. Typically about long, they have a special feeding structure called a ...
or
Ectoprocta Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies. Typically about long, they have a special feeding structure called ...
*****Phylum Brachiopoda *****Phylum Phoronida *****Phylum Mollusca *****Phylum Sipunculoidea *****Phylum Echiuroidea *****Phylum Annelida *****Phylum
Arthropoda Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chitin, ...
****Subgrade Enterocoela *****Phylum Brachiata or Pogonophora *****Phylum
Chaetognatha The Chaetognatha or chaetognaths (meaning ''bristle-jaws'') are a phylum of predatory marine worms that are a major component of plankton worldwide. Commonly known as arrow worms, about 20% of the known Chaetognatha species are benthic, and ca ...
*****Phylum
Echinodermata An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the s ...
*****Phylum Hemichordata *****Phylum Chordata


Six kingdoms

In 1977,
Carl Woese Carl Richard Woese (; July 15, 1928 – December 30, 2012) was an American microbiologist and biophysicist. Woese is famous for defining the Archaea (a new domain of life) in 1977 through a pioneering phylogenetic taxonomy of 16S ribosomal RNA, ...
and colleagues proposed the fundamental subdivision of the prokaryotes into the Eubacteria (later called the Bacteria) and Archaebacteria (later called the Archaea), based on
ribosomal RNA Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes. Ribosomal RNA is transcribed from ribosom ...
structure; this would later lead to the proposal of three "domains" of life, of Bacteria, Archaea, and Eukaryota. Combined with the five-kingdom model, this created a six-kingdom model, where the kingdom Monera is replaced by the kingdoms Bacteria and Archaea. This six-kingdom model is commonly used in recent US high school biology textbooks, but has received criticism for compromising the current scientific consensus.{{Cite journal , last=Case , first=Emily , date=2008-10-01 , title=Teaching Taxonomy: How Many Kingdoms? , url=https://eric.ed.gov/?id=EJ813862 , access-date=2020-07-28 , journal= American Biology Teacher , volume=70 , issue=8 , pages=472–477 , doi=10.2307/30163328 , jstor=30163328 , language=en But the division of prokaryotes into two kingdoms remains in use with the recent seven kingdoms scheme of Thomas Cavalier-Smith, although it primarily differs in that Protista is replaced by Protozoa and
Chromista Chromista is a biological kingdom consisting of single-celled and multicellular eukaryotic species that share similar features in their photosynthetic organelles ( plastids). It includes all protists whose plastids contain chlorophyll ''c'', ...
. {{clade , label1=  Life   , 1={{clade , 1={{clade , label1=Empire
Prokaryota A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Connec ...
, 1={{clade , 1=Kingdom
Eubacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were amon ...
(Bacteria) , 2=Kingdom
Archaebacteria Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebact ...
(Archaea) , 2={{clade , label1=Empire Eukaryota , 1={{clade , 1=Kingdom
Protista A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the exc ...
or Protoctista , 2=Kingdom
Plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclu ...
ae , 3=Kingdom
Fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
, 4=Kingdom
Animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
ia


Eight kingdoms

Thomas Cavalier-Smith Thomas (Tom) Cavalier-Smith, FRS, FRSC, NERC Professorial Fellow (21 October 1942 – 19 March 2021), was a professor of evolutionary biology in the Department of Zoology, at the University of Oxford. His research has led to discov ...
supported the consensus at that time, that the difference between
Eubacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were amon ...
and
Archaebacteria Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebact ...
was so great (particularly considering the genetic distance of ribosomal genes) that the prokaryotes needed to be separated into two different kingdoms. He then divided
Eubacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were amon ...
into two subkingdoms: Negibacteria (
Gram negative The gram (originally gramme; SI unit symbol g) is a unit of mass in the International System of Units (SI) equal to one one thousandth of a kilogram. Originally defined as of 1795 as "the absolute weight of a volume of pure water equal to th ...
bacteria) and Posibacteria (
Gram positive In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. Gram-positive bact ...
bacteria). Technological advances in electron microscopy allowed the separation of the
Chromista Chromista is a biological kingdom consisting of single-celled and multicellular eukaryotic species that share similar features in their photosynthetic organelles ( plastids). It includes all protists whose plastids contain chlorophyll ''c'', ...
from the
Plantae Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclude ...
kingdom. Indeed, the chloroplast of the chromists is located in the lumen of the endoplasmic reticulum instead of in the
cytosol The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells ( intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondri ...
. Moreover, only chromists contain
chlorophyll c Chlorophyll ''c'' is a form of chlorophyll found in certain marine algae, including the photosynthetic Chromista (e.g. diatoms and brown algae) and dinoflagellates. It has a blue-green color and is an accessory pigment, particularly significant i ...
. Since then, many non-photosynthetic phyla of protists, thought to have secondarily lost their chloroplasts, were integrated into the kingdom Chromista. Finally, some protists lacking mitochondria were discovered. As mitochondria were known to be the result of the
endosymbiosis An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship. (The term endosymbiosis is from the Greek: ἔνδον ''endon'' "within ...
of a
proteobacterium Pseudomonadota (synonym Proteobacteria) is a major phylum of Gram-negative bacteria. The renaming of phyla in 2021 remains controversial among microbiologists, many of whom continue to use the earlier names of long standing in the literature. The ...
, it was thought that these amitochondriate eukaryotes were primitively so, marking an important step in
eukaryogenesis Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bact ...
. As a result, these amitochondriate protists were separated from the protist kingdom, giving rise to the, at the same time, superkingdom and kingdom
Archezoa Archezoa was a kingdom proposed in the 20th century by Thomas Cavalier-Smith (1942–2021), and was believed to encompass eukaryotes which did not have mitochondria (and are therefore ''amitochondriate'') or peroxisomes (e.g. '' Giardia''). The c ...
. This superkingdom was opposed to the Metakaryota superkingdom, grouping together the five other eukaryotic kingdoms ( Animalia, Protozoa,
Fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
,
Plantae Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclude ...
and
Chromista Chromista is a biological kingdom consisting of single-celled and multicellular eukaryotic species that share similar features in their photosynthetic organelles ( plastids). It includes all protists whose plastids contain chlorophyll ''c'', ...
). This was known as the Archezoa hypothesis, which has since been abandoned; later schemes did not include the Archezoa–Metakaryota divide. {{clade , label1=  Life   , 1={{clade , 1={{clade , label1=Superkingdom
Prokaryota A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Connec ...
, 1={{clade , 1=Kingdom
Eubacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were amon ...
, 2=Kingdom
Archaebacteria Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebact ...
, 2={{clade , label1=Superkingdom
Archezoa Archezoa was a kingdom proposed in the 20th century by Thomas Cavalier-Smith (1942–2021), and was believed to encompass eukaryotes which did not have mitochondria (and are therefore ''amitochondriate'') or peroxisomes (e.g. '' Giardia''). The c ...
‡ , 1={{clade , 1=Kingdom
Archezoa Archezoa was a kingdom proposed in the 20th century by Thomas Cavalier-Smith (1942–2021), and was believed to encompass eukaryotes which did not have mitochondria (and are therefore ''amitochondriate'') or peroxisomes (e.g. '' Giardia''). The c ...
‡ , 3={{clade , label1=Superkingdom Metakaryota‡ , 1={{clade , 1=Kingdom Protozoa , 2=Kingdom
Chromista Chromista is a biological kingdom consisting of single-celled and multicellular eukaryotic species that share similar features in their photosynthetic organelles ( plastids). It includes all protists whose plastids contain chlorophyll ''c'', ...
, 3=Kingdom
Plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclu ...
ae , 4=Kingdom
Fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
, 5=Kingdom
Animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
ia ‡ No longer recognized by
taxonomists In biology, taxonomy () is the scientific study of naming, defining ( circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grouped into taxa (singular: taxon) and these groups are given ...
.


Six kingdoms (1998)

In 1998, Cavalier-Smith published a six-kingdom model, which has been revised in subsequent papers. The version published in 2009 is shown below.{{cite journal , last=Cavalier-Smith , first=Thomas , author-link=Thomas Cavalier-Smith , year=2009 , title=Kingdoms Protozoa and Chromista and the eozoan root of the eukaryotic tree , journal=Biology Letters , volume=6 , issue=3 , pages=342–345 , doi=10.1098/rsbl.2009.0948 , pmc=2880060 , pmid=20031978Compared to the version Cavalier-Smith published in 2004, the
alveolates The alveolates (meaning "pitted like a honeycomb") are a group of protists, considered a major clade and superphylum within Eukarya. They are currently grouped with the stramenopiles and Rhizaria among the protists with tubulocristate mitochond ...
and the
rhizaria The Rhizaria are an ill-defined but species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are all non-photosynthethic, but many forami ...
ns have been moved from Kingdom Protozoa to Kingdom Chromista. Cavalier-Smith no longer accepted the importance of the fundamental Eubacteria–Archaebacteria divide put forward by Woese and others and supported by recent research. The kingdom
Bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
(sole kingdom of empire
Prokaryota A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Connec ...
) was subdivided into two sub-kingdoms according to their membrane topologies: Unibacteria and Negibacteria. Unibacteria was divided into phyla
Archaebacteria Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebact ...
and Posibacteria; the bimembranous-unimembranous transition was thought to be far more fundamental than the long branch of genetic distance of Archaebacteria, viewed as having no particular biological significance. Cavalier-Smith does not accept the requirement for taxa to be monophyletic ("holophyletic" in his terminology) to be valid. He defines Prokaryota, Bacteria, Negibacteria, Unibacteria, and Posibacteria as valid paraphyla (therefore "monophyletic" in the sense he uses this term) taxa, marking important innovations of biological significance (in regard of the concept of biological
niche Niche may refer to: Science *Developmental niche, a concept for understanding the cultural context of child development *Ecological niche, a term describing the relational position of an organism's species *Niche differentiation, in ecology, the ...
). In the same way, his paraphyletic kingdom Protozoa includes the ancestors of Animalia, Fungi, Plantae, and Chromista. The advances of phylogenetic studies allowed Cavalier-Smith to realize that all the phyla thought to be
archezoa Archezoa was a kingdom proposed in the 20th century by Thomas Cavalier-Smith (1942–2021), and was believed to encompass eukaryotes which did not have mitochondria (and are therefore ''amitochondriate'') or peroxisomes (e.g. '' Giardia''). The c ...
ns (i.e. primitively amitochondriate eukaryotes) had in fact secondarily lost their mitochondria, typically by transforming them into new organelles:
Hydrogenosome A hydrogenosome is a membrane-enclosed organelle found in some anaerobic ciliates, flagellates, and fungi. Hydrogenosomes are highly variable organelles that have presumably evolved from protomitochondria to produce molecular hydrogen and ATP i ...
s. This means that all living eukaryotes are in fact metakaryotes, according to the significance of the term given by Cavalier-Smith. Some of the members of the defunct kingdom
Archezoa Archezoa was a kingdom proposed in the 20th century by Thomas Cavalier-Smith (1942–2021), and was believed to encompass eukaryotes which did not have mitochondria (and are therefore ''amitochondriate'') or peroxisomes (e.g. '' Giardia''). The c ...
, like the phylum
Microsporidia Microsporidia are a group of spore-forming unicellular parasites. These spores contain an extrusion apparatus that has a coiled polar tube ending in an anchoring disc at the apical part of the spore. They were once considered protozoans or pr ...
, were reclassified into kingdom
Fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
. Others were reclassified in kingdom Protozoa, like Metamonada which is now part of infrakingdom
Excavata Excavata is a major supergroup of unicellular organisms belonging to the domain Eukaryota. It was first suggested by Simpson and Patterson in 1999 and introduced by Thomas Cavalier-Smith in 2002 as a formal taxon. It contains a variety of free- ...
. Because Cavalier-Smith allows paraphyly, the diagram below is an 'organization chart', not an 'ancestor chart', and does not represent an evolutionary tree. {{clade , label1=  Life   , 1={{clade , 1={{clade , label1=Empire
Prokaryota A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Connec ...
, 1={{clade , 1=Kingdom
Bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
— includes
Archaebacteria Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebact ...
as part of a subkingdom , 2={{clade , label1=Empire Eukaryota , 1={{clade , 1=Kingdom Protozoa — e.g. Amoebozoa, Choanozoa,
Excavata Excavata is a major supergroup of unicellular organisms belonging to the domain Eukaryota. It was first suggested by Simpson and Patterson in 1999 and introduced by Thomas Cavalier-Smith in 2002 as a formal taxon. It contains a variety of free- ...
, 2=Kingdom
Chromista Chromista is a biological kingdom consisting of single-celled and multicellular eukaryotic species that share similar features in their photosynthetic organelles ( plastids). It includes all protists whose plastids contain chlorophyll ''c'', ...
— e.g. Alveolata, cryptophytes,
Heterokonta Heterokonts are a group of protists (formally referred to as Heterokonta, Heterokontae or Heterokontophyta). The group is a major line of eukaryotes. Most are algae, ranging from the giant multicellular kelp to the unicellular diatoms, which a ...
(
Brown Algae Brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Northern Hemisphere. Brown algae are the major seaweeds of the temperate and p ...
,
Diatoms A diatom (New Latin, Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group com ...
etc.),
Haptophyta The haptophytes, classified either as the Haptophyta, Haptophytina or Prymnesiophyta (named for '' Prymnesium''), are a clade of algae. The names Haptophyceae or Prymnesiophyceae are sometimes used instead. This ending implies classification at ...
,
Rhizaria The Rhizaria are an ill-defined but species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are all non-photosynthethic, but many forami ...
, 3=Kingdom
Plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclu ...
ae — e.g.
glaucophyte The glaucophytes, also known as glaucocystophytes or glaucocystids, are a small group of unicellular algae found in freshwater and moist terrestrial environments, less common today than they were during the Proterozoic. The stated number of speci ...
s,
red Red is the color at the long wavelength end of the visible spectrum of light, next to orange and opposite violet. It has a dominant wavelength of approximately 625–740 nanometres. It is a primary color in the RGB color model and a secondar ...
and
green alga The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...
e,
land plants The Embryophyta (), or land plants, are the most familiar group of green plants that comprise vegetation on Earth. Embryophytes () have a common ancestor with green algae, having emerged within the Phragmoplastophyta clade of green algae as sist ...
, 4=Kingdom
Fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
, 5=Kingdom
Animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
ia {, role="presentation" class="wikitable mw-collapsible mw-collapsed" , + {{nowrap, Cavalier-Smith's six kingdom system (1998) , -style="font-size: 80%;vertical-align: top;background: white" , , {{nowrap, Kingdom
Bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
{{br     Subkingdom Negibacteria{{br         Infrakingdom Lipobacteria{{br             Superphylum Eobacteria{{br         Phylum Heliobacteria{{br         Phylum Hadobacteria{{br           Subphylum Chlorobacteria{{br           Subphylum Deinobacteria{{br       Superphylum Endoflagellata{{br         Phylum Spirochaetae{{br           Subphylum Euspirochaetae{{br           Subphylum Leptospirae{{br     Infrakingdom Glycobacteria{{br       Superphylum Pimelobacteria{{br         Phylum Sphingobacteria{{br           Subphylum Chlorobibacteria{{br           Subphylum Flavobacteria{{br         Phylum Eurybacteria{{br           Subphylum Sclenobacteria{{br           Subphylum Fusobacteria{{br           Subphylum Fibrobacteria{{br         Phylum Cyanobacteria{{br           Subphylum Gloeobacteria{{br           Subphylum Phycobacteria{{br         Phylum Proteobacteria{{br           Subphylum Rhodobacteria{{br             Infraphylum Alphabacteria{{br             Infraphylum Chromatibacteria{{br           Subphylum Thiobacteria{{br       Superphylum Planctobacteria{{br         Phylum Planctobacteria{{br   Subkingdom Unibacteria{{br     Infrakingdom Posibacteria{{br       Phylum Posibacteria{{br         Subphylum Teichobacteria{{br           Infraphylum Endobacteria{{br           Infraphylum Actinobacteria{{br         Subphylum Togobacteria{{br     Infrakingdom
Archaebacteria Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebact ...
{{br       Phylum Mendosicutes{{br         Subphylum Euryarcheota{{br           Infraphylum Halomebacteria{{br           Infraphylum Eurytherma{{br         Subphylum Sulfobacteria{{br , , {{nowrap, Kingdom Protozoa{{br   Subkingdom
Archezoa Archezoa was a kingdom proposed in the 20th century by Thomas Cavalier-Smith (1942–2021), and was believed to encompass eukaryotes which did not have mitochondria (and are therefore ''amitochondriate'') or peroxisomes (e.g. '' Giardia''). The c ...
{{br     Phylum Metamonada{{br       Subphylum Eopharyngia{{br       Subphylum Axostylaria{{br     Phylum Trichozoa{{br       Subphylum Anaeromonada{{br       Subphylum Parabasala{{br   Subkingdom Neozoa{{br     Infrakingdom Sarcomastigota{{br       Phylum Neomonada{{br         Subphylum Apusozoa{{br         Subphylum Isomita{{br         Subphylum Choanozoa{{br       Phylum Cercozoa{{br         Subphylum Phytomyxa{{br         Subphylum Reticulofilosa{{br         Subphylum Monadofilosa{{br       Phylum Foraminifera{{br       Phylum Amoebozoa{{br         Subphylum Lobosa{{br         Subphylum Conosa{{br           Infraphylum Archamoebae{{br           Infraphylum Mycetozoa{{br             Superclass Eumyxa{{br             Superclass Dictyostelia{{br     Infrakingdom Discicristata{{br       Phylum Percolozoa{{br         Subphylum Tetramitia{{br         Subphylum Pseudociliata{{br       Phylum Euglenozoa{{br         Subphylum Plicostoma{{br         Subphylum Saccostoma{{br     Infrakingdom Alveolata{{br       Superphylum Miozoa{{br         Phylum Dinozoa{{br           Subphylum Protalveolata{{br           Subphylum Dinoflagellata{{br         Phylum
Sporozoa The Apicomplexa (also called Apicomplexia) are a large phylum of parasitic alveolates. Most of them possess a unique form of organelle that comprises a type of non-photosynthetic plastid called an apicoplast, and an apical complex structure. The ...
{{br           Subphylum Gregarinae{{br           Subphylum Coccidiomorpha{{br           Subphylum Manubrispora{{br       Superphylum Heterokaryota{{br         Phylum
Ciliophora The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to eukaryotic flagella, but are in general shorter and present in much larger numbers, with a different ...
{{br           Subphylum Tubulicorticata{{br           Subphylum Epiplasmata{{br           Subphylum Filocorticata{{br     Infrakingdom Actinopod, Actinopoda{{br       Phylum Heliozoa{{br       Phylum Radiozoa{{br         Subphylum Spasmaria{{br         Subphylum Radiolaria{{br , , {{nowrap, Kingdom
Fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
{{br   Subkingdom Eomycota{{br     Phylum Archemycota{{br       Subphylum Dictyomycotina{{br         Class Chytridiomycetes{{br           Subclass Rumpomycetidae{{br           Subclass Spizomycetidae{{br         Class Enteromycetes{{br       Subphylum Melanomycotina{{br         Infraphylum Allomycotina{{br           Class Allomycetes{{br         Infraphylum Zygomycotina{{br           Superclass Eozygomycetia{{br             Class Bolomycetes{{br             Class Glomomycetes{{br           Superclass Neozygomycetia{{br             Class Zygomycetes{{br               Subclass Mucoromycetidae{{br               Subclass Meromycetidae{{br             Class Zoomycetes{{br               Subclass Entomycetidae{{br               Subclass Pedomycetidae{{br                 Superorder Trichomycetalia{{br                 Superorder Pyxomycetalia{{br     Phylum
Microsporidia Microsporidia are a group of spore-forming unicellular parasites. These spores contain an extrusion apparatus that has a coiled polar tube ending in an anchoring disc at the apical part of the spore. They were once considered protozoans or pr ...
{{br       Class Minisporea{{br       Class Microsporea{{br         Subclass Pleistophorea{{br         Subclas Disporea{{br   Subkingdom Neomycota{{br     Phylum Ascomycota{{br       Subphylum Hemiascomycotina{{br         Class Taphrinomycetes{{br         Class Geomycetes{{br         Class Endomycetes{{br           Subclass Dipomycetidae{{br           Subclass Saccharomycetidae{{br       Subphylum Euascomycotina{{br         Class Discomycetes{{br           Subclass Calycomycetidae{{br           Subclass Lecomycetidae{{br           Subclass Pezomycetidae{{br         Class Pyrenomycetes{{br           Subclass Verrucomycetidae{{br           Subclass Ostiomycetidae{{br         Class Loculomycetes{{br           Subclass Dendromycetidae{{br           Subclass Loculoascomycetidae{{br         Class Plectomycetes{{br     Phylum Basidiomycota{{br       Subphylum Septomycotina{{br         Class Septomycetes{{br           Subclass Sporidiomycetidae{{br           Subclass Uredomycetidae{{br       Subphylum Orthomycotina{{br         Superclass Hemibasidiomycetia{{br           Class Ustomycetes{{br         Superclass Hymenomycetia{{br           Class Gelimycetes{{br             Subclass Tremellomycetidae{{br             Subclass Dacrymycetidae{{br             Subclass Auromycetidae{{br           Class Homobasidiomycetes{{br             Subclass Clavomycetidae{{br             Subclass Pileomycetidae , , {{nowrap, Kingdom Animalia{{br   Subkingdom
Radiata Radiata or Radiates is a historical taxonomic rank that was used to classify animals with radially symmetric body plans. The term Radiata is no longer accepted, as it united several different groupings of animals that do not form a monophyletic ...
{{br     Infrakingdom Spongiaria{{br       Phylum Porifera{{br         Subphylum Hyalospongiae{{br         Subphylum Calcispongiae{{br         Subphylum
Archaeocyatha Archaeocyatha (or archaeocyathids 'ancient cups') is a taxon of extinct, sessile, reef-building marine sponges that lived in warm tropical and subtropical waters during the Cambrian Period. It is believed that the centre of the Archaeocyatha or ...
{{extinct{{br     Infrakingdom Coelenterata{{br       Phylum
Cnidaria Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter. Their distinguishing feature is cnidocytes, specialized cells that ...
{{br         Subphylum Anthozoa{{br         Subphylum Medusozoa{{br     Infrakingdom Placozoa{{br       Phylum Placozoa{{br   Subkingdom Myxozoa{{br     Phylum Myxosporidia{{br   Subkingdom Bilateria{{br     Branch Protostomia{{br       Infrakingdom Lophozoa{{br         Superphylum Polyzoa{{br           Phylum
Bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies. Typically about long, they have a special feeding structure called a ...
{{br             Subphylum Gymnolaemata{{br             Subphylum Lophopoda{{br           Phylum Kamptozoa{{br             Subphylum
Entoprocta Entoprocta (), or Kamptozoa , is a phylum of mostly sessile aquatic animals, ranging from long. Mature individuals are goblet-shaped, on relatively long stalks. They have a "crown" of solid tentacles whose cilia generate water currents that ...
{{br             Subphylum Cycliophora{{br         Superphylum Conchozoa{{br           Phylum Mollusca{{br             Subphylum Bivalvia{{br             Subphylum Glossophora{{br               Infraphylum Univalvia{{br               Infraphylum Spiculata{{br               Infraphylum Cephalopoda{{br           Phylum Brachiozoa{{br             Subphylum Brachiopoda{{br             Subphylum Phoronida{{br         Superphylum Sipuncula{{br           Phylum Sipuncula{{br         Superphylum Vermizoa{{br           Phylum Annelida{{br             Subphylum Polychaeta{{br               Infraphylum Operculata{{br               Infraphylum Pharyngata{{br             Subphylum Clitellata{{br             Subphylum Echiura{{br             Subphylum Pogonophora{{br           Phylum Nemertina{{br       Infrakingdom Chaetognathi{{br         Phylum
Chaetognatha The Chaetognatha or chaetognaths (meaning ''bristle-jaws'') are a phylum of predatory marine worms that are a major component of plankton worldwide. Commonly known as arrow worms, about 20% of the known Chaetognatha species are benthic, and ca ...
{{br       Infrakingdom Ecdysozoa{{br         Superphylum Haemopoda{{br           Phylum
Arthropoda Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chitin, ...
{{br             Subphylum Cheliceromorpha{{br               Infraphylum Pycnogonida{{br               Infraphylum Chelicerata{{br             Subphylum Trilobitomorpha {{extinct{{br             Subphylum Mandibulata{{br               Infraphylum Crustacea{{br               Infraphylum Myriapoda{{br               Infraphylum Insecta{{br           Phylum Lobopoda{{br             Subphylum Onychophora{{br             Subphylum Tardigrada{{br         Superphylum Nemathelminthes{{br           Phylum Nemathelminthes{{br             Subphylum Scalidorhyncha{{br               Infraphylum Priapozoa{{br               Infraphylum Kinorhyncha{{br             Subphylum Nematoida{{br               Infraphylum Nematoda{{br               Infraphylum Nematomorpha{{br       Infrakingdom Platyzoa{{br         Phylum Acanthognatha{{br           Subphylum Trochata{{br             Infraphylum Rotifera{{br             Infraphylum
Acanthocephala Acanthocephala (Greek , ', thorn + , ', head) is a phylum of parasitic worms known as acanthocephalans, thorny-headed worms, or spiny-headed worms, characterized by the presence of an eversible proboscis, armed with spines, which it uses to p ...
{{br           Subphylum Monokonta{{br         Phylum
Platyhelminthes The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") are a phylum of relatively simple bilaterian, unsegme ...
{{br           Subphylum Turbellaria{{br             Infraphylum Mucorhabda{{br             Infraphylum Rhabditophora{{br           Subphylum Neodermata{{br             Infraphylum Trematoda{{br             Infraphylum Cercomeromorpha{{br     Branch
Deuterostomia Deuterostomia (; in Greek) are animals typically characterized by their anus forming before their mouth during embryonic development. The group's sister clade is Protostomia, animals whose digestive tract development is more varied. Some ex ...
{{br       Infrakingdom Coelomopora{{br         Phylum Hemichordata{{br           Subphylum Pterobranchia{{br           Subphylum Enteropneusta{{br         Phylum
Echinodermata An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the s ...
{{br           Subphylum Homalozoa{{br           Subphylum Pelmatozoa{{br             Infraphylum Blastozoa{{br             Infraphylum Crinozoa{{br           Subphylum Eleutherozoa{{br             Infraphylum Asterozoa{{br             Infraphylum Echinozoa{{br       Infrakingdom Chordonia{{br         Phylum Urochorda{{br           Subphylum Tunicata{{br             Infraphylum Ascidiae{{br             Infraphylum Thaliae{{br           Subphylum Appendicularia{{br         Phylum Chordata{{br           Subphylum Acraniata{{br             Infraphylum Cephalochordata{{br             Infraphylum Conodonta {{extinct{{br           Subphylum Vertebrata{{br             Infraphylum Agnatha{{br             Infraphylum Gnathostomata{{br   Subkingdom
Mesozoa The Mesozoa are minuscule, worm-like parasites of marine invertebrates. Generally, these tiny, elusive creatures consist of a somatoderm (outer layer) of ciliated cells surrounding one or more reproductive cells. A recent study recovered Mesoz ...
{{br     Phylum
Mesozoa The Mesozoa are minuscule, worm-like parasites of marine invertebrates. Generally, these tiny, elusive creatures consist of a somatoderm (outer layer) of ciliated cells surrounding one or more reproductive cells. A recent study recovered Mesoz ...
, , {{nowrap, Kingdom
Plantae Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclude ...
{{br   Subkingdom Biliphyta{{br     Infrakingdom Glaucophyta{{br       Phylum Glaucophyta{{br     Infrakingdom Rhodophyta{{br       Phylum Rhodophyta{{br         Subphylum Rhodellophytina{{br         Subphylum Macrorhodophytina{{br   Subkingdom Viridiplantae{{br     Infrakingdom
Chlorophyta Chlorophyta or Prasinophyta is a taxon of green algae informally called chlorophytes. The name is used in two very different senses, so care is needed to determine the use by a particular author. In older classification systems, it refers to a ...
{{br       Phylum
Chlorophyta Chlorophyta or Prasinophyta is a taxon of green algae informally called chlorophytes. The name is used in two very different senses, so care is needed to determine the use by a particular author. In older classification systems, it refers to a ...
{{br         Subphylum Chlorophytina{{br           Infraphylum Prasinophytae{{br           Infraphylum Tetraphytae{{br         Subphylum Phragmophytina{{br           Infraphylum Charophytae{{br           Infraphylum Rudophytae{{br     Infrakingdom Cormophyta{{br       Phylum Bryophyta{{br         Subphylum Hepaticae{{br         Subphylum Anthocerotae{{br         Subphylum Musci{{br           Infraphylum Sphagneae{{br           Infraphylum Bryatae{{br       Phylum
Tracheophyta Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They a ...
{{br         Subphylum Pteridophytina{{br           Infraphylum Psilophytae{{br           Infraphylum Lycophytae{{br           Infraphylum Sphenophytae{{br           Infraphylum Filices{{br         Subphylum Spermatophytina{{br           Infraphylum Gymnospermae{{br           Infraphylum Angiospermae , , {{nowrap, Kingdom
Chromista Chromista is a biological kingdom consisting of single-celled and multicellular eukaryotic species that share similar features in their photosynthetic organelles ( plastids). It includes all protists whose plastids contain chlorophyll ''c'', ...
{{br   Subkingdom Cryptista{{br     Phylum Cryptophyta{{br   Subkingdom Chromobiota{{br     Infrakingdom
Heterokonta Heterokonts are a group of protists (formally referred to as Heterokonta, Heterokontae or Heterokontophyta). The group is a major line of eukaryotes. Most are algae, ranging from the giant multicellular kelp to the unicellular diatoms, which a ...
{{br       Superphylum Sagenista{{br         Phylum Sagenista{{br           Subphylum Bicoecia{{br           Subphylum Labyrinthista{{br         Phylum Ochrophyta{{br           Subphylum Phaeista{{br             Infraphylum Hypogyrista{{br             Infraphylum Chrysista{{br           Subphylum Diatomeae{{br         Phylum Bigyra{{br           Subphylum Bigyromonada{{br           Subphylum Pseudofungi{{br           Subphylum Opalinata{{br     Infrakingdom
Haptophyta The haptophytes, classified either as the Haptophyta, Haptophytina or Prymnesiophyta (named for '' Prymnesium''), are a clade of algae. The names Haptophyceae or Prymnesiophyceae are sometimes used instead. This ending implies classification at ...
{{br       Phylum
Haptophyta The haptophytes, classified either as the Haptophyta, Haptophytina or Prymnesiophyta (named for '' Prymnesium''), are a clade of algae. The names Haptophyceae or Prymnesiophyceae are sometimes used instead. This ending implies classification at ...


Seven kingdoms

Cavalier-Smith and his collaborators revised their classification in 2015. In this scheme they introduced two superkingdoms of Prokaryota and Eukaryota and seven kingdoms. Prokaryota have two kingdoms:
Bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
and Archaea. (This was based on the consensus in the Bacterial taxonomy, Taxonomic Outline of Bacteria and Archaea, and the Catalogue of Life). The Eukaryota have five kingdoms: Protozoa, Chromista, Plantae, Fungi, and Animalia. In this classification a protist is any of the eukaryotic unicellular organisms.{{cite journal , last1=Ruggiero , first1=Michael A. , last2=Gordon , first2=Dennis P. , last3=Orrell , first3=Thomas M. , last4=Bailly , first4=Nicolas , last5=Bourgoin , first5=Thierry , last6=Brusca , first6=Richard C. , last7=Cavalier-Smith , first7=Thomas , last8=Guiry , first8=Michael D. , last9=Kirk , first9=Paul M. , last10=Thuesen , first10=Erik V. , title=A higher level classification of all living organisms , journal=PLOS ONE , date=2015 , volume=10 , issue=4 , pages=e0119248 , doi=10.1371/journal.pone.0119248 , pmid=25923521 , pmc=4418965 , bibcode=2015PLoSO..1019248R , doi-access=free {{clade , label1=  Life   , 1={{clade , 1={{clade , label1=Superkingdom
Prokaryota A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Connec ...
, 1={{clade , 1=Kingdom
Bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
, 2=Kingdom Archaea , 2={{clade , label1=Superkingdom Eukaryota , 1={{clade , 1=Kingdom Protozoa — e.g. Amoebozoa, Choanozoa,
Excavata Excavata is a major supergroup of unicellular organisms belonging to the domain Eukaryota. It was first suggested by Simpson and Patterson in 1999 and introduced by Thomas Cavalier-Smith in 2002 as a formal taxon. It contains a variety of free- ...
, 2=Kingdom
Chromista Chromista is a biological kingdom consisting of single-celled and multicellular eukaryotic species that share similar features in their photosynthetic organelles ( plastids). It includes all protists whose plastids contain chlorophyll ''c'', ...
— e.g. Alveolata, cryptophytes,
Heterokonta Heterokonts are a group of protists (formally referred to as Heterokonta, Heterokontae or Heterokontophyta). The group is a major line of eukaryotes. Most are algae, ranging from the giant multicellular kelp to the unicellular diatoms, which a ...
(
Brown Algae Brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Northern Hemisphere. Brown algae are the major seaweeds of the temperate and p ...
,
Diatoms A diatom (New Latin, Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group com ...
etc.),
Haptophyta The haptophytes, classified either as the Haptophyta, Haptophytina or Prymnesiophyta (named for '' Prymnesium''), are a clade of algae. The names Haptophyceae or Prymnesiophyceae are sometimes used instead. This ending implies classification at ...
,
Rhizaria The Rhizaria are an ill-defined but species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are all non-photosynthethic, but many forami ...
, 3=Kingdom
Plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclu ...
ae — e.g.
glaucophyte The glaucophytes, also known as glaucocystophytes or glaucocystids, are a small group of unicellular algae found in freshwater and moist terrestrial environments, less common today than they were during the Proterozoic. The stated number of speci ...
s,
red Red is the color at the long wavelength end of the visible spectrum of light, next to orange and opposite violet. It has a dominant wavelength of approximately 625–740 nanometres. It is a primary color in the RGB color model and a secondar ...
and
green alga The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...
e,
land plants The Embryophyta (), or land plants, are the most familiar group of green plants that comprise vegetation on Earth. Embryophytes () have a common ancestor with green algae, having emerged within the Phragmoplastophyta clade of green algae as sist ...
, 4=Kingdom
Fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
, 5=Kingdom
Animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
ia


Summary

{{Full biological kingdom classification The kingdom-level classification of life is still widely employed as a useful way of grouping organisms, notwithstanding some problems with this approach: * Kingdoms such as Protozoa represent evolutionary grade, grades rather than clades, and so are rejected by cladistics, phylogenetic classification systems. * The most recent research does not support the classification of the eukaryotes into any of the standard systems. {{As of, 2010, April, no set of kingdoms is sufficiently supported by research to attain widespread acceptance. In 2009, Andrew Roger and Alastair Simpson emphasized the need for diligence in analyzing new discoveries: "With the current pace of change in our understanding of the eukaryote tree of life, we should proceed with caution."


Beyond traditional kingdoms

{{anchor, Modern view While the concept of kingdoms continues to be used by some taxonomists, there has been a movement away from traditional kingdoms, as they are no longer seen as providing a Cladistics, cladistic classification, where there is emphasis in arranging organisms into Clade, natural groups.


Three domains of life

{{main, Three-domain system, Domain (biology) {{PhylomapB, , caption=A phylogenetic tree based on rRNA data showing Woese's three-domain system. All smaller branches can be considered kingdoms., size = 440px From around the mid-1970s onwards, there was an increasing emphasis on comparisons of genes at the molecular level (initially ribosome, ribosomal ribonucleic acid, RNA genes) as the primary factor in classification; genetic similarity was stressed over outward appearances and behavior. Taxonomic ranks, including kingdoms, were to be groups of organisms with a common ancestor, whether monophyletic (''all'' descendants of a common ancestor) or paraphyletic (''only some'' descendants of a common ancestor).{{citation needed, date=January 2017 Based on such RNA studies,
Carl Woese Carl Richard Woese (; July 15, 1928 – December 30, 2012) was an American microbiologist and biophysicist. Woese is famous for defining the Archaea (a new domain of life) in 1977 through a pioneering phylogenetic taxonomy of 16S ribosomal RNA, ...
thought life could be divided into three large divisions and referred to them as the "three primary kingdom" model or "urkingdom" model.{{cite journal , last1=Balch , first1=W.E. , last2=Magrum , first2=L.J. , last3=Fox , first3=G.E. , last4=Wolfe , first4=C.R. , last5=Woese , first5=C.R. , name-list-style=amp , date=August 1977 , title=An ancient divergence among the bacteria , journal=Journal of Molecular Evolution , volume=9 , issue=4 , pages=305–311 , doi=10.1007/BF01796092 , pmid=408502 , bibcode=1977JMolE...9..305B , s2cid=27788891 In 1990, the name "domain" was proposed for the highest rank. This term represents a synonym for the category of dominion (lat. dominium), introduced by Moore in 1974.{{cite journal , last=Moore , first=R.T. , year=1974 , title=Proposal for the recognition of super ranks , journal=Taxon , volume=23 , issue=4 , pages=650–652 , doi=10.2307/1218807 , jstor=1218807 , url=http://www.iapt-taxon.org/historic/Congress/IBC_1975/Prop034bis-037.pdf Unlike Moore, Woese et al. (1990) did not suggest a Latin term for this category, which represents a further argument supporting the accurately introduced term dominion.{{cite journal , last=Luketa , first=S. , year=2012 , title = New views on the megaclassification of life , journal=Protistology , volume=7 , issue=4 , pages=218–237 , url=http://protistology.ifmo.ru/num7_4/luketa_protistology_7-4.pdf Woese divided the prokaryotes (previously classified as the Kingdom Monera) into two groups, called bacteria, Eubacteria and Archaea, Archaebacteria, stressing that there was as much genetic difference between these two groups as between either of them and all eukaryotes. {{clade , label1=  Life   , 1={{clade , 1=Domain
Bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
(
Eubacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were amon ...
) , 2=Domain Archaea (
Archaebacteria Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebact ...
) , 3=Domain Eukaryote, Eukarya (Eukaryota) According to genetic data, although eukaryote groups such as plants, fungi, and animals may look different, they are more closely related to each other than they are to either the Eubacteria or Archaea. It was also found that the eukaryotes are more closely related to the Archaea than they are to the Eubacteria. Although the primacy of the Eubacteria-Archaea divide has been questioned, it has been upheld by subsequent research.{{cite journal , last1=Dagan , first1=T. , last2=Roettger , first2=M. , last3=Bryant , last4=Martin , first4=W. , year=2010 , title=Genome Networks Root the Tree of Life between Prokaryotic Domains , journal=Genome Biology and Evolution , volume=2 , pages=379–92 , doi=10.1093/gbe/evq025 , pmid=20624742 , pmc=2997548 , name-list-style=amp There is no consensus on how many kingdoms exist in the classification scheme proposed by Woese.


Eukaryotic supergroups

{{anchor, Kingdoms of the Eukaryota {{Main, Supergroup (biology) In 2004, a review article by Simpson and Roger noted that the Protista were "a Wastebasket taxon, grab-bag for all eukaryotes that are not animals, plants or fungi". They held that only monophyletic groups should be accepted as formal ranks in a classification and that – while this approach had been impractical previously (necessitating "literally dozens of eukaryotic 'kingdoms{{'") – it had now become possible to divide the eukaryotes into "just a few major groups that are probably all monophyletic".{{cite journal , title=The real 'kingdoms' of eukaryotes , last1=Simpson , first1=Alastair G.B. , last2=Roger , first2=Andrew J. , journal=Current Biology , volume=14 , issue=17 , pages=R693–R696 , doi=10.1016/j.cub.2004.08.038 , pmid=15341755, year=2004 , s2cid=207051421 , doi-access=free On this basis, the diagram opposite (redrawn from their article) showed the real "kingdoms" (their quotation marks) of the eukaryotes. A classification which followed this approach was produced in 2005 for the International Society of Protistologists, by a committee which "worked in collaboration with specialists from many societies". It divided the eukaryotes into the same six "supergroups".{{cite journal , vauthors=Adl SM, ((Simpson AGB)), Farmer MA, Andersen RA, Anderson OR, Barta JR, Bowser SS, Brugerolle G, Fensome RA, Fredericq S, James TY, Karpov S, Kugrens P, Krug J, Lane CE, Lewis LA, Lodge J, Lynn DH, Mann DG, Mccourt RM, Mendoza L, Moestrup Ø, Mozley-Standridge SE, Nerad TA, Shearer CA, Smirnov AV, Spiegel FW, Taylor MF , display-authors=6 , title=The new higher-level classification of eukaryotes with emphasis on the taxonomy of protists , journal=Journal of Eukaryotic Microbiology , year=2005 , volume=52 , issue=5 , pages=399–451 , doi=10.1111/j.1550-7408.2005.00053.x , pmid=16248873 , s2cid=8060916 , doi-access=free The published classification deliberately did not use formal taxonomic ranks, including that of "kingdom". {{clade , label1=  Life   , 1={{clade , 1={{clade , label1=Domain
Bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
  , 1={{clade , 1= prokaryotic
Bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
, 2={{clade , label1=Domain Archaea   , 1={{clade , 1= prokaryotic Archaeans , 3={{clade , label1=Domain Eukaryota   , 1={{clade , label1=
Excavata Excavata is a major supergroup of unicellular organisms belonging to the domain Eukaryota. It was first suggested by Simpson and Patterson in 1999 and introduced by Thomas Cavalier-Smith in 2002 as a formal taxon. It contains a variety of free- ...
  , 1= various flagellate protozoa , label2=   Amoebozoa   , 2= most lobose amoeboids and slime moulds , label3=   Opisthokonta   , 3=
animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
s, fungus, fungi, choanoflagellates, etc. , label4=  
Rhizaria The Rhizaria are an ill-defined but species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are all non-photosynthethic, but many forami ...
  , 4= Foraminifera, Radiolaria, and various other amoeboid protozoa , label5=   Chromalveolate, Chromalveolata   , 5= Heterokont, Stramenopiles (Brown Algae, Brown Algae, Diatoms etc.), haptophyte, Haptophyta, cryptomonad, Cryptophyta (or cryptomonads), and alveolate, Alveolata , label6=   Archaeplastida (or Primoplantae)  , 6= Embryophyte, Land plants,
green alga The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...
e, red algae, and
glaucophyte The glaucophytes, also known as glaucocystophytes or glaucocystids, are a small group of unicellular algae found in freshwater and moist terrestrial environments, less common today than they were during the Proterozoic. The stated number of speci ...
s In this system the multicellular animals (Metazoa) are descended from the same ancestor as both the unicellular choanoflagellates and the fungi which form the Opisthokonta. Plants are thought to be more distantly related to animals and fungi. However, in the same year as the International Society of Protistologists' classification was published (2005), doubts were being expressed as to whether some of these supergroups were monophyletic, particularly the Chromalveolata, and a review in 2006 noted the lack of evidence for several of the six proposed supergroups.{{cite journal , last1=Parfrey , first1=Laura W. , last2=Barbero , first2=Erika , last3=Lasser , first3=Elyse , last4=Dunthorn , first4=Micah , year=2006 , last5=Bhattacharya , first5=Debashish , last6=Patterson , first6=David J. , last7=Katz , first7=Laura A. , name-list-style=amp , title=Evaluating support for the current classification of eukaryotic diversity , journal=PLOS Genetics , volume=2 , issue=12 , pages=e220 , doi=10.1371/journal.pgen.0020220 , pmid=17194223 , pmc=1713255 {{As of, 2010, there is widespread agreement that the Rhizaria belong with the Stramenopiles and the Alveolata, in a clade dubbed the SAR supergroup,{{Harvnb, Burki, Shalchian-Tabrizi, Minge, Skjæveland , 2007, p=4 so that Rhizaria is not one of the main eukaryote groups.{{cite journal , last1=Burki , first1=Fabien , last2=Shalchian-Tabrizi , first2=Kamran , last3=Pawlowski , first3=Jan , year=2008 , title=Phylogenomics reveals a new 'megagroup' including most photosynthetic eukaryotes , journal=Biology Letters , pmid=18522922 , volume=4 , issue=4 , pmc=2610160 , pages=366–369 , doi=10.1098/rsbl.2008.0224 , name-list-style=amp{{cite journal , last1=Burki , first1=F. , last2=Inagaki , year=2009 , first2=Y. , last3=Brate , first3=J. , last4=Archibald , first4=J. M. , last5=Keeling , first5=P. J. , last6=Cavalier-Smith , first6=T. , last7=Sakaguchi , first7=M. , last8=Hashimoto , first8=T. , last9=Horak , first9=A. , last10=Kumar , first10=S. , last11=Klaveness , first11=D., author-link11=Dag Klaveness (limnologist) , last12=Jakobsen , first12=K. S. , last13=Pawlowski , first13=J. , last14=Shalchian-Tabrizi , first14=K. , title=Large-scale phylogenomic analyses reveal that two enigmatic protist lineages, Telonemia and Centroheliozoa, are related to photosynthetic Chromalveolates , journal=Genome Biology and Evolution , volume=1 , pages=231–238 , doi=10.1093/gbe/evp022 , pmc=2817417 , pmid=20333193 , display-authors=8{{cite journal , last1=Hackett , first1=J.D. , last2=Yoon , first2=H.S. , last3=Li , first3=S. , last4=Reyes-Prieto , first4=A., last5=Rummele , first5=S.E. , last6=Bhattacharya , first6=D. , name-list-style=amp , year=2007 , title=Phylogenomic analysis supports the monophyly of cryptophytes and haptophytes and the association of Rhizaria with chromalveolates , journal=Molecular Biology and Evolution , volume=24 , issue=8 , pages=1702–1713 , doi=10.1093/molbev/msm089 , pmid=17488740 , doi-access=free Beyond this, there does not appear to be a consensus. Rogozin ''et al.'' in 2009 noted that "The deep phylogeny of eukaryotes is an extremely difficult and controversial problem."{{cite journal , last1=Rogozin , first1=I.B. , last2=Basu , first2=M.K. , last3=Csürös , first3=M., last4=Koonin , first4=E.V. , year=2009 , title=Analysis of rare genomic changes does not support the unikont–bikont phylogeny, and suggests cyanobacterial symbiosis as the point of primary radiation of eukaryotes , journal=Genome Biology and Evolution , volume=1 , pages=99–113 , doi=10.1093/gbe/evp011 , pmc=2817406 , name-list-style=amp , pmid=20333181 {{As of, 2010, December, there appears to be a consensus that the six supergroup model proposed in 2005 does not reflect the true phylogeny of the eukaryotes and hence how they should be classified, although there is no agreement as to the model which should replace it.{{cite journal , last1=Burki , first1=Fabien , last2=Shalchian-Tabrizi , first2=Kamran , last3=Minge , first3=Marianne , last4=Skjæveland , first4=Åsmund , last5=Nikolaev , first5=Sergey I. , last6=Jakobsen , first6=Kjetill S. , last7=Pawlowski , first7=Jan , name-list-style=amp , editor1-last=Butler , year=2007 , editor1-first=Geraldine , title=Phylogenomics reshuffles the eukaryotic supergroups , journal=PLOS ONE , volume=2 , issue=8 , pages=e790 , doi=10.1371/journal.pone.0000790 , pmid=17726520 , pmc=1949142 , bibcode=2007PLoSO...2..790B , doi-access=free{{cite journal , last1=Kim , first1=E. , last2=Graham , first2=L. E. , year=2008 , title=EEF2 analysis challenges the monophyly of Archaeplastida and Chromalveolata , journal=PLOS ONE , volume=3 , issue=7 , pages=e2621 , editor1-last=Redfield , editor1-first=Rosemary Jeanne , doi=10.1371/journal.pone.0002621 , pmid=18612431 , pmc=2440802 , name-list-style=amp , last3=Redfield , first3=Rosemary Jeanne , bibcode=2008PLoSO...3.2621K , author3-link=Rosemary Redfield , doi-access=free{{clear


Comparison of top level classification

{{further, Tree of life (biology)#Proposals for top levels Some authors have added non-cellular life to their classifications. This can create a "superdomain" called "Acytota", also called "Aphanobionta", of non-cellular life; with the other superdomain being "cytota" or cellular life.{{cite journal , author=Trifonov EN, Kejnovsky E , title=Acytota - associated kingdom of neglected life. , journal=J Biomol Struct Dyn , year=2016 , volume= 34 , issue= 8 , pages=1641–8 , pmid=26305806 , doi=10.1080/07391102.2015.1086959 , pmc= , s2cid=38178747 , url=https://pubmed.ncbi.nlm.nih.gov/26305806/{{cite book , title=Biological systematics: The state of the art , publication-place=London , isbn=0-412-36440-9 , oclc=27895507 , page= , last1=Minelli , first1=Alessandro , year=1993 The eocyte hypothesis proposes that the eukaryotes emerged from a phylum within the archaea called the Thermoproteota (formerly known as eocytes or Crenarchaeota).{{cite journal , first1=John M. , last1=Archibald , title=The eocyte hypothesis and the origin of eukaryotic cells , journal=PNAS , volume=105 , issue=51 , pages=20049–20050 , date=23 December 2008 , doi=10.1073/pnas.0811118106, pmid=19091952 , bibcode=2008PNAS..10520049A , pmc=2629348 , doi-access=free {{cite journal , first1=James A. , last1= Lake , first2=Eric , last2=Henderson , first3=Melanie , last3=Oakes , first4=Michael W. , last4=Clark , title=Eocytes: A new ribosome structure indicates a kingdom with a close relationship to eukaryotes , journal=PNAS , volume=81 , pages=3786–3790 , date=June 1984 , issue=12 , doi=10.1073/pnas.81.12.3786 , pmid=6587394 , pmc=345305 , bibcode=1984PNAS...81.3786L , doi-access=free {{biological classification with acellular


Viruses

The International Committee on Taxonomy of Viruses uses the taxonomic rank "kingdom" for the classification of viruses (with the suffix ''-virae''); but this is beneath the top level classifications of Realm (virology), realm and subrealm.{{cite web , url=https://talk.ictvonline.org/information/w/ictv-information/383/ictv-code , title=ICTV Code , website=talk.ictvonline.org , publisher=International Committee on Taxonomy of Viruses , access-date=26 April 2020 There is ongoing debate as to whether viruses can be included in the tree of life. The arguments against include the fact that they are obligate intracellular parasites that lack metabolism and are not capable of Self-replication, replication outside of a host cell.{{cite journal , last=Moreira , first=David , author2=Purificación López-García , title=Ten reasons to exclude viruses from the tree of life , journal=Nature Reviews Microbiology , year=2009 , volume=7 , pages=306–311 , issue=4 , doi=10.1038/nrmicro2108 , pmid=19270719 , s2cid=3907750{{cite journal , title=New views on the megaclassification of life , journal=Protistology , date=2012 , first=Stefan , last=Luketa , volume=7 , issue=4 , pages=218–237 , url=http://protistology.ifmo.ru/num7_4/luketa_protistology_7-4.pdf Another argument is that their placement in the tree would be problematic, since it is suspected that viruses have arisen multiple times{{citation needed, date=October 2019, and they have a penchant for harvesting nucleotide sequences from their hosts. On the other hand, arguments favor their inclusion.{{cite journal , last1=Hegde , first1=Nagendra , first2=Mohan S. , last2=Maddur , first3=Srini V. , last3=Kaveri , first4=Jagadeesh , last4=Bayry , name-list-style=amp , title=Reasons to include viruses in the tree of life , journal=Nature Reviews Microbiology , year=2009 , volume=7 , pages=615 , issue=8 , doi=10.1038/nrmicro2108-c1 , pmid=19561628 , doi-access=free One comes from the discovery of unusually large and complex viruses, such as Mimivirus, that possess typical cellular genes.{{cite journal , last1=Raoult , first1=Didier , first2=Stéphane , last2=Audic , first3=Catherine , last3=Robert , first4=Chantal , last4=Abergel , first5=Patricia , last5=Renesto , first6=Hiroyuki , last6=Ogata , first7=Bernard , last7=La Scola , first8=Marie , last8=Suzan , first9=Jean-Michel , last9=Claverie , title=The 1.2 megabase genome sequence of Mimivirus , journal=Science (journal), Science , year=2004 , volume=306 , pages=1344–1350 , doi=10.1126/science.1101485 , bibcode=2004Sci...306.1344R , pmid=15486256 , issue=5700, s2cid=84298461


See also

{{portal, Biology * Cladistics * Phylogenetics * Systematics * Taxonomy (biology), Taxonomy


Notes

{{notelist


References

{{reflist, refs= {{cite journal , last1=Woese , first1=C.R. , last2=Kandler , first2=O. , last3=Wheelis , first3=M.L. , year=1990 , title=Towards a natural systs: proposal for the domains Archaea, Bacteria, and Eucarya , journal=Proceedings of the National Academy of Sciences of the United States of America , volume=87 , issue=12 , pages=4576–9 , pmid=2112744 , pmc=54159 , doi=10.1073/pnas.87.12.4576 , bibcode=1990PNAS...87.4576W , doi-access=free


Further reading

* Pelentier, B. (2007-2015). ''Empire Biota: a comprehensive taxonomy''

[Historical overview.] * Peter H. Raven and Helena Curtis (1970), ''Biology of Plants'', New York: Worth Publishers. [Early presentation of five-kingdom system.]


External links


A Brief History of the Kingdoms of Life
at Earthling Nature



{{Taxonomic ranks {{DEFAULTSORT:Rank01 Kingdoms (biology), Biology terminology, Kingdom