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,

, 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 ...

and

. 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.

(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

of prokaryotic organisms; as a revised phylum Monera of the Protista, it included organisms now classified as

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

. 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

*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 The ''Actinomycetota'' (or ''Actinobacteria'') are a phylum of all gram-positive bacteria. They can be terrestrial or aquatic. They are of great economic importance to humans because agriculture and forests depend on their contributions to so ...

**Phylum

Spirochaetae A spirochaete () or spirochete is a member of the phylum Spirochaetota (), (synonym Spirochaetes) which contains distinctive diderm (double-membrane) gram-negative bacteria, most of which have long, helically coiled (corkscrew-shaped or ...

, , Kingdom

*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 Hyphochytrids are eukaryotic organisms in the group of Stramenopiles (Heterokonta). Characteristics They are distinguished by an anterior tinsel flagellum on their zoospores. Also they have a rhizoidal or hypha-like vegetative system (hence the ...

*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 An amoeba (; less commonly spelled ameba or amœba; plural ''am(o)ebas'' or ''am(o)ebae'' ), often called an amoeboid, is a type of cell or unicellular organism with the ability to alter its shape, primarily by extending and retracting pseudopo ...

*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 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 ...

*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

*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 ...

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 American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the "United States" or "America" ** Americans, citizens and nationals of the United States of America ** American ancestry, pe ...

, 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

or Protoctista , 2=Kingdom

ae , 3=Kingdom

, 4=Kingdom

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

and

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

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 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 ...

(

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

from the

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,

and

). 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

, 1={{clade , 1=Kingdom

, 2=Kingdom

, 2={{clade , label1=Superkingdom

‡ , 1={{clade , 1=Kingdom

‡ , 3={{clade , label1=Superkingdom Metakaryota‡ , 1={{clade , 1=Kingdom Protozoa , 2=Kingdom

, 3=Kingdom

ae , 4=Kingdom

, 5=Kingdom

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

(sole kingdom of empire

) was subdivided into two sub-kingdoms according to their membrane topologies: Unibacteria and Negibacteria. Unibacteria was divided into phyla

and

; 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

, 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

. 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

, 1={{clade , 1=Kingdom

— includes

as part of a subkingdom , 2={{clade , label1=Empire Eukaryota , 1={{clade , 1=Kingdom Protozoa — e.g. Amoebozoa, Choanozoa,

, 2=Kingdom

— 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

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 ...

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 ...

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

, 5=Kingdom

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

{{br Subkingdom Negibacteria{{br Infrakingdom Lipobacteria{{br Superphylum

Eobacteria Eobacteria is a proposed clade characterized by Cavalier-Smith. Species in this group lack lipopolysaccharide. The clade includes Hadobacteria and Chlorobacteria The Chloroflexota are a phylum of bacteria containing isolates with a diversity ...

{{br Phylum

Heliobacteria Heliobacteria are a unique subset of prokaryotic bacteria that process light for energy. Distinguishable from other phototrophic bacteria, they utilize a unique photosynthetic pigment, bacteriochlorophyll ''g'' and are the only known Gram-posit ...

{{br Phylum

Hadobacteria ''Deinococcota'' (synonym, ''Deinococcus-Thermus'') is a phylum of bacteria with a single class, ''Deinococci'', that are highly resistant to environmental hazards, also known as extremophiles. These bacteria have thick cell walls that give them ...

{{br Subphylum

Chlorobacteria The Chloroflexota are a phylum of bacteria containing isolates with a diversity of phenotypes, including members that are aerobic thermophiles, which use oxygen and grow well in high temperatures; anoxygenic phototrophs, which use light for phot ...

{{br Subphylum Deinobacteria{{br Superphylum Endoflagellata{{br Phylum

{{br Subphylum Euspirochaetae{{br Subphylum Leptospirae{{br Infrakingdom Glycobacteria{{br Superphylum Pimelobacteria{{br Phylum Sphingobacteria{{br Subphylum Chlorobibacteria{{br Subphylum

Flavobacteria The class Flavobacteriia is composed of a single order of environmental bacteria. According to Bernardet ''et al''., Flavobacteriia are Gram-negative aerobic rods, 2–5 μm long, 0.3–0.5 μm wide, with rounded or tapered end ...

{{br Phylum

Eurybacteria Eurybacteria is a taxon created by Cavalier-Smith, which includes several groups of Gram-negative bacteria. In this model, it is the ancestor of gram positive bacteria. Their endospores are characterized by producing and presenting external flage ...

{{br Subphylum Sclenobacteria{{br Subphylum

Fusobacteria Fusobacteriota are obligately anaerobic non-sporeforming Gram-negative bacilli. Since the first reports in the late nineteenth century, various names have been applied to these organisms, sometimes with the same name being applied to different s ...

{{br Subphylum Fibrobacteria{{br Phylum Cyanobacteria{{br Subphylum

Gloeobacteria ''Gloeobacter'' is a genus of cyanobacteria. It is the sister group to all other cyanobacteria. ''Gloeobacter'' is unique among cyanobacteria in not having thylakoids, which are characteristic for all other cyanobacteria and chloroplasts. Ins ...

{{br Subphylum Phycobacteria{{br Phylum

Proteobacteria 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 ...

{{br Subphylum Rhodobacteria{{br Infraphylum

Alphabacteria Alphaproteobacteria is a class of bacteria in the phylum Pseudomonadota (formerly Proteobacteria). The Magnetococcales and Mariprofundales are considered basal or sister to the Alphaproteobacteria. The Alphaproteobacteria are highly diverse an ...

{{br Infraphylum Chromatibacteria{{br Subphylum Thiobacteria{{br Superphylum

Planctobacteria The PVC superphylum is a superphylum of bacteria named after its three important members, Planctomycetota, Verrucomicrobiota, and Chlamydiota. Cavalier-Smith postulated that the PVC bacteria probably lost or reduced their peptidoglycan cell wall ...

{{br Phylum

{{br Subkingdom Unibacteria{{br Infrakingdom

{{br Phylum

{{br Subphylum Teichobacteria{{br Infraphylum Endobacteria{{br Infraphylum

Actinobacteria The ''Actinomycetota'' (or ''Actinobacteria'') are a phylum of all gram-positive bacteria. They can be terrestrial or aquatic. They are of great economic importance to humans because agriculture and forests depend on their contributions to so ...

{{br Subphylum Togobacteria{{br Infrakingdom

{{br Phylum

Mendosicutes 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 Archaeba ...

{{br Subphylum Euryarcheota{{br Infraphylum

Halomebacteria Haloarchaea (halophilic archaea, halophilic archaebacteria, halobacteria) are a class of the Euryarchaeota, found in water saturated or nearly saturated with salt. Halobacteria are now recognized as archaea rather than bacteria and are one of ...

{{br Infraphylum Eurytherma{{br Subphylum Sulfobacteria{{br , , {{nowrap, Kingdom Protozoa{{br Subkingdom

{{br Phylum Metamonada{{br Subphylum

Eopharyngia Trichozoa is a group of excavates. "Fornicata" is a similar grouping, but it excludes Parabasalia.Tree
a ...

{{br Subphylum Axostylaria{{br Phylum

Trichozoa Trichozoa is a group of excavates. "Fornicata" is a similar grouping, but it excludes Parabasalia.Tree
a ...

{{br Subphylum

Anaeromonada Anaeromonadea is a class of excavates, comprising the oxymonads and ''Trimastix ''Trimastix'' is a genus of excavates, the sole occupant of the order Trimastigida. ''Trimastix'' are bacterivorous, free living and anaerobic. When first observ ...

{{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 Reticulofilosa is a grouping of Rhizaria. It includes Chlorarachnea ('' Chlorarachnion, Bigelowiella, Lotharella The chlorarachniophytes are a small group of exclusively marine algae widely distributed in tropical and temperate waters. The ...

{{br Subphylum

Monadofilosa Monadofilosa is a grouping of Cercozoa. (It is sometimes considered one of three, the other two being Phytomyxa and Reticulofilosa.) These organisms are single-celled amoeboid protists. Classification Monadofilosa includes the testaceans, wh ...

{{br Phylum

Foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...

{{br Phylum Amoebozoa{{br Subphylum

Lobosa Lobosa is a taxonomic group of amoebae in the phylum Amoebozoa. Most lobosans possess broad, bluntly rounded pseudopods, although one genus in the group, the recently discovered ''Sapocribrum,'' has slender and threadlike (filose) pseudopodia. ...

{{br Subphylum

Conosa Conosa is a grouping of Amoebozoa. It is subdivided into three groups – Archamoebae, Variosea ( paraphyletic) and Mycetozoa (polyphyletic). In some classifications, the mycetozoan Myxogastria and Dictyostelia are united in Macromyceto ...

{{br Infraphylum Archamoebae{{br Infraphylum

Mycetozoa Mycetozoa is a polyphyletic grouping of slime molds. It was originally thought to be a monophyletic clade, but recently it was discovered that protostelia are a polyphyletic group within Conosa. Classification It can be divided into dictyoste ...

{{br Superclass Eumyxa{{br Superclass Dictyostelia{{br Infrakingdom

Discicristata Discicristata is a proposed eukaryotic clade. It consists of Euglenozoa plus Percolozoa. It was proposed that Discicristata plus Cercozoa yielded Cabozoa. Another proposal is to group Discicristata with Jakobida into Discoba superphylum. See ...

{{br Phylum

Percolozoa The Percolozoa are a group of colourless, non-photosynthetic Excavata, including many that can transform between amoeboid, flagellate, and cyst stages. Characteristics Most Percolozoa are found as bacterivores in soil, fresh water and occasio ...

{{br Subphylum Tetramitia{{br Subphylum Pseudociliata{{br Phylum Euglenozoa{{br Subphylum Plicostoma{{br Subphylum Saccostoma{{br Infrakingdom Alveolata{{br Superphylum

Miozoa Myzozoa is a grouping of specific phyla within Alveolata, that either feed through myzocytosis, or were ancestrally capable of feeding through myzocytosis. Many protozoan orders are included within Myzozoa. It is sometimes described as a phyl ...

{{br Phylum Dinozoa{{br Subphylum Protalveolata{{br Subphylum Dinoflagellata{{br Phylum

{{br Subphylum Gregarinae{{br Subphylum Coccidiomorpha{{br Subphylum Manubrispora{{br Superphylum Heterokaryota{{br Phylum

{{br Subphylum Tubulicorticata{{br Subphylum Epiplasmata{{br Subphylum Filocorticata{{br Infrakingdom Actinopoda{{br Phylum

Heliozoa Heliozoa, commonly known as sun-animalcules, are microbial eukaryotes ( protists) with stiff arms ( axopodia) radiating from their spherical bodies, which are responsible for their common name. The axopodia are microtubule-supported projections f ...

{{br Phylum Radiozoa{{br Subphylum Spasmaria{{br Subphylum

Radiolaria The Radiolaria, also called Radiozoa, are protozoa of diameter 0.1–0.2 mm that produce intricate mineral skeletons, typically with a central capsule dividing the cell into the inner and outer portions of endoplasm and ectoplasm. The el ...

{{br , , {{nowrap, Kingdom

{{br Subkingdom Eomycota{{br Phylum Archemycota{{br Subphylum Dictyomycotina{{br Class

Chytridiomycetes Chytridiomycetes () is a class of fungi. Members are found in soil, fresh water, and saline estuaries. They are first known from the Rhynie chert. It has recently been redefined to exclude the taxa Neocallimastigomycota and Monoblepharidomycet ...

{{br Subclass Rumpomycetidae{{br Subclass Spizomycetidae{{br Class Enteromycetes{{br Subphylum Melanomycotina{{br Infraphylum Allomycotina{{br Class Allomycetes{{br Infraphylum

Zygomycotina 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 ...

{{br Superclass Eozygomycetia{{br Class Bolomycetes{{br Class Glomomycetes{{br Superclass Neozygomycetia{{br Class

Zygomycetes Zygomycota, or zygote fungi, is a former phylum, division or phylum of the kingdom Fungi. The members are now part of two Phylum, phyla: the Mucoromycota and Zoopagomycotina, Zoopagomycota. Approximately 1060 species are known. They are mostly t ...

{{br Subclass Mucoromycetidae{{br Subclass Meromycetidae{{br Class Zoomycetes{{br Subclass Entomycetidae{{br Subclass Pedomycetidae{{br Superorder Trichomycetalia{{br Superorder Pyxomycetalia{{br Phylum

{{br Class Minisporea{{br Class Microsporea{{br Subclass Pleistophorea{{br Subclas Disporea{{br Subkingdom Neomycota{{br Phylum Ascomycota{{br Subphylum Hemiascomycotina{{br Class

Taphrinomycetes The Taphrinomycetes are a class of ascomycete fungi belonging to the subdivision Taphrinomycotina. It includes the single order Taphrinales, which includes 2 families, 8 genera and 140 species In biology, a species is the basic unit of ...

{{br Class Geomycetes{{br Class Endomycetes{{br Subclass Dipomycetidae{{br Subclass

Saccharomycetidae Saccharomycetales belongs to the kingdom of Fungi and the division Ascomycota. It is the only order in the class Saccharomycetes. There are currently 13 families recognized as belonging to Saccharomycetales. GBIF also includes; Alloascoideaceae ...

{{br Subphylum Euascomycotina{{br Class Discomycetes{{br Subclass Calycomycetidae{{br Subclass Lecomycetidae{{br Subclass Pezomycetidae{{br Class

Pyrenomycetes Sordariomycetes is a class of fungi in the subdivision Pezizomycotina (Ascomycota), consisting of 28 orders, 90 families, 1344 genera. Sordariomycetes is from the Latin sordes (filth) because some species grow in animal feces, though growth habi ...

{{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

{{br Infrakingdom Spongiaria{{br Phylum Porifera{{br Subphylum Hyalospongiae{{br Subphylum Calcispongiae{{br Subphylum

{{extinct{{br Infrakingdom

Coelenterata Coelenterata is a term encompassing the animal phyla Cnidaria (coral animals, true jellies, sea anemones, sea pens, and their relatives) and Ctenophora (comb jellies). The name comes , referring to the hollow body cavity common to these two phyla ...

{{br Phylum

{{br Subphylum Anthozoa{{br Subphylum

Medusozoa Medusozoa is a clade in the phylum Cnidaria, and is often considered a subphylum. It includes the classes Hydrozoa, Scyphozoa, Staurozoa and Cubozoa, and possibly the parasitic Polypodiozoa. Medusozoans are distinguished by having a medusa sta ...

{{br Infrakingdom

Placozoa The Placozoa are a basal form of marine free-living (non-parasitic) multicellular organism. They are the simplest in structure of all animals. Three genera have been found: the classical ''Trichoplax adhaerens'', '' Hoilungia hongkongensis'', a ...

{{br Phylum

{{br Subkingdom

Myxozoa Myxozoa (etymology: Greek: μύξα ''myxa'' "slime" or "mucus" + thematic vowel o + ζῷον ''zoon'' "animal") is a subphylum of aquatic cnidarian animals – all obligate parasites. It contains the smallest animals ever known to have lived. O ...

{{br Phylum

Myxosporidia Myxosporea is a class of microscopic parasites, belonging to the Myxozoa clade within Cnidaria. They have a complex life cycle which comprises vegetative forms in two hosts, an aquatic invertebrate (generally an annelid but sometimes a bryozoan) ...

{{br Subkingdom Bilateria{{br Branch Protostomia{{br Infrakingdom Lophozoa{{br Superphylum

Polyzoa 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 Phylum

{{br Subphylum

Gymnolaemata Gymnolaemata are a class of Bryozoans. Gymnolaemata are sessile, mostly marine organisms and grow on the surfaces of rocks, kelp, and in some cases on animals, like fish. Zooids are cylindrical or flattened. The lophophore is protruded by action ...

{{br Subphylum Lophopoda{{br Phylum Kamptozoa{{br Subphylum

{{br Subphylum

Cycliophora ''Symbion'' is a genus of commensal aquatic animals, less than 0.5 mm wide, found living attached to the mouthparts of cold-water lobsters. They have sac-like bodies, and three distinctly different forms in different parts of their two-sta ...

{{br Superphylum Conchozoa{{br Phylum Mollusca{{br Subphylum

Bivalvia Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, biva ...

{{br Subphylum Glossophora{{br Infraphylum

Univalvia The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. The ...

{{br Infraphylum Spiculata{{br Infraphylum

Cephalopoda A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent hea ...

{{br Phylum

Brachiozoa Brachiozoa is a grouping of lophophorate animals including Brachiopoda and Phoronida. It also includes their ancestors, the extinct tommotiids. References Lophophorata Protostome unranked clades {{Protostome-stub ...

{{br Subphylum Brachiopoda{{br Subphylum Phoronida{{br Superphylum

Sipuncula The Sipuncula or Sipunculida (common names sipunculid worms or peanut worms) is a class containing about 162 species of unsegmented marine annelid worms. The name ''Sipuncula'' is from the genus name ''Sipunculus'', and comes from the Latin ' ...

{{br Phylum

{{br Superphylum Vermizoa{{br Phylum Annelida{{br Subphylum

Polychaeta Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which ar ...

{{br Infraphylum Operculata{{br Infraphylum Pharyngata{{br Subphylum

Clitellata The Clitellata are a class of annelid worms, characterized by having a clitellum - the 'collar' that forms a reproductive cocoon during part of their life cycles. The clitellates comprise around 8,000 species. Unlike the class of Polychaeta, ...

{{br Subphylum

Echiura The Echiura, or spoon worms, are a small group of marine animals. Once treated as a separate phylum, they are now considered to belong to Annelida. Annelids typically have their bodies divided into segments, but echiurans have secondarily los ...

{{br Subphylum Pogonophora{{br Phylum Nemertina{{br Infrakingdom Chaetognathi{{br Phylum

{{br Infrakingdom Ecdysozoa{{br Superphylum Haemopoda{{br Phylum

{{br Subphylum Cheliceromorpha{{br Infraphylum

Pycnogonida Sea spiders are marine arthropods of the order Pantopoda ( ‘all feet’), belonging to the class Pycnogonida, hence they are also called pycnogonids (; named after ''Pycnogonum'', the type genus; with the suffix '). They are cosmopolitan, foun ...

{{br Infraphylum

Chelicerata The subphylum Chelicerata (from New Latin, , ) constitutes one of the major subdivisions of the phylum Arthropoda. It contains the sea spiders, horseshoe crabs, and arachnids (including harvestmen, scorpions, spiders, solifuges, ticks, and mi ...

{{br Subphylum

Trilobitomorpha The Artiopoda is a grouping of extinct arthropods that includes trilobites and their close relatives. It was erected by Hou and Bergström in 1997 to encompass a wide diversity of arthropods that would traditionally have been assigned to the Trilo ...

{{extinct{{br Subphylum

Mandibulata Mandibulata, termed "mandibulates", is a clade of arthropods that comprises the extant subphyla Myriapoda (millipedes and others), Crustacea and Hexapoda (insects and others). Mandibulata is currently believed to be the sister group of the clade ...

{{br Infraphylum Crustacea{{br Infraphylum

Myriapoda Myriapods () are the members of subphylum Myriapoda, containing arthropods such as millipedes and centipedes. The group contains about 13,000 species, all of them terrestrial. The fossil record of myriapods reaches back into the late Silurian ...

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Insecta Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs o ...

{{br Phylum Lobopoda{{br Subphylum

Onychophora Onychophora (from grc, ονυχής, , "claws"; and , , "to carry"), commonly known as velvet worms (due to their velvety texture and somewhat wormlike appearance) or more ambiguously as peripatus (after the first described genus, '' Peripatus ...

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Tardigrada Tardigrades (), known colloquially as water bears or moss piglets, are a phylum of eight-legged segmented micro-animals. They were first described by the German zoologist Johann August Ephraim Goeze in 1773, who called them Kleiner Wasserbä ...

{{br Superphylum Nemathelminthes{{br Phylum Nemathelminthes{{br Subphylum Scalidorhyncha{{br Infraphylum Priapozoa{{br Infraphylum

Kinorhyncha Kinorhyncha ( grc, κινέω, kīnéō, I move, ' "snout") is a phylum of small marine invertebrates that are widespread in mud or sand at all depths as part of the meiobenthos. They are also called mud dragons. Modern species are or less, ...

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Nematoida Nematoida is a grouping of animals, including the roundworms The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-parasitic nematodes also known ...

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Nematoda The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a broa ...

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Nematomorpha Nematomorpha (sometimes called Gordiacea, and commonly known as horsehair worms, hairsnakes, or Gordian worms) are a phylum of parasitoid animals superficially similar to nematode worms in morphology, hence the name. Most species range in size f ...

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Platyzoa The paraphyletic "Platyzoa" are a group of protostome unsegmented animals proposed by Thomas Cavalier-Smith in 1998. Cavalier-Smith included in Platyzoa the phylum Platyhelminthes (or flatworms), and a new phylum, the Acanthognatha, into whic ...

{{br Phylum Acanthognatha{{br Subphylum Trochata{{br Infraphylum

Rotifera The rotifers (, from the Latin , "wheel", and , "bearing"), commonly called wheel animals or wheel animalcules, make up a phylum (Rotifera ) of microscopic and near-microscopic pseudocoelomate animals. They were first described by Rev. John H ...

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{{br Subphylum Monokonta{{br Phylum

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Turbellaria The Turbellaria are one of the traditional sub-divisions of the phylum Platyhelminthes (flatworms), and include all the sub-groups that are not exclusively parasitic. There are about 4,500 species, which range from to large freshwater forms mor ...

{{br Infraphylum Mucorhabda{{br Infraphylum

Rhabditophora Rhabditophora (from ''rhabdito''-, rhabdite + Greek -φορος ''phoros'' bearer, i.e., "rhabdite bearers") is a class of flatworms. It includes all parasitic flatworms (clade Neodermata) and most free-living species that were previously group ...

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Neodermata Neodermata is a clade of rhabditophoran flatworms containing the parasitic groups Trematoda, Monogenea and Cestoda. Description All neodermatans are parasites, in many groups having a free-swimming larval stage. The most striking feature unit ...

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Trematoda Trematoda is a class of flatworms known as flukes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive h ...

{{br Infraphylum Cercomeromorpha{{br Branch

{{br Infrakingdom Coelomopora{{br Phylum Hemichordata{{br Subphylum

Pterobranchia Pterobranchia is a class of small worm-shaped animals. They belong to the Hemichordata, and live in secreted tubes on the ocean floor. Pterobranchia feed by filtering plankton out of the water with the help of cilia attached to tentacles. The ...

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Enteropneusta The acorn worms or Enteropneusta are a hemichordate class of invertebrates consisting of one order of the same name. The closest non-hemichordate relatives of the Enteropneusta are the echinoderms. There are 111 known species of acorn worm in the ...

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Homalozoa Homalozoa is an obsolete extinct subphylum of Paleozoic era echinoderms, prehistoric marine invertebrates. They are also referred to as carpoids. Description The Homalozoa lacked the typical pentamer body form of other echinoderms, but all were ...

{{br Subphylum Pelmatozoa{{br Infraphylum

Blastozoa Blastozoa is a subphylum of extinct animals belonging to Phylum Echinodermata. This subphylum is characterized by the presence of specialized respiratory structures and brachiole plates used for feeding. This subphylum ranged from the Cambrian to ...

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Crinozoa Crinozoa is a subphylum of mostly sessile echinoderms, of which the crinoids, or sea lilies, are the only extant members. Crinozoans have an extremely extensive fossil history, which may or may not extend into the Precambrian (provided the enigm ...

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Eleutherozoa Eleutherozoa is a proposed subphylum of echinoderms. They are mobile animals with the mouth directed towards the substrate. They usually have a madreporite, tube feet, and moveable spines of some sort, and some have Tiedemann's bodies on the r ...

{{br Infraphylum Asterozoa{{br Infraphylum

Echinozoa Echinozoa is a subphylum of free-living echinoderms in which the body is or originally was a modified globe with meridional symmetry. Echinozoans lack arms, brachioles, or other appendages, and do not at any time exhibit pinnate structure. Their t ...

{{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 A cephalochordate (from Greek: κεφαλή ''kephalé'', "head" and χορδή ''khordé'', "chord") is an animal in the chordate subphylum, Cephalochordata. They are commonly called lancelets. Cephalochordates possess 5 synapomorphies, or prima ...

{{br Infraphylum Conodonta {{extinct{{br Subphylum

Vertebrata Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

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Agnatha Agnatha (, Ancient Greek 'without jaws') is an infraphylum of jawless fish in the phylum Chordata, subphylum Vertebrata, consisting of both present (cyclostomes) and extinct (conodonts and ostracoderms) species. Among recent animals, cyclosto ...

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Gnathostomata Gnathostomata (; from Greek: (') "jaw" + (') "mouth") are the jawed vertebrates. Gnathostome diversity comprises roughly 60,000 species, which accounts for 99% of all living vertebrates, including humans. In addition to opposing jaws, livin