In biology , a kingdom is the second highest taxonomic rank , just below domain . Kingdoms are divided into smaller groups called phyla (singular phylum).
48-506: 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 from Ancient Greek κοῖλος ( koîlos ) 'hollow' and ἔντερον ( énteron ) 'intestine', referring to the hollow body cavity common to these two phyla. They have very simple tissue organization, with only two layers of cells ( ectoderm and endoderm ), along with
96-484: A phylum ( / ˈ f aɪ l əm / ; pl. : phyla ) is a level of classification or taxonomic rank below kingdom and above class . Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature for algae, fungi, and plants accepts the terms as equivalent. Depending on definitions, the animal kingdom Animalia contains about 31 phyla,
144-556: A certain degree of morphological or developmental similarity (the phenetic definition), or a group of organisms with a certain degree of evolutionary relatedness (the phylogenetic definition). Attempting to define a level of the Linnean hierarchy without referring to (evolutionary) relatedness is unsatisfactory, but a phenetic definition is useful when addressing questions of a morphological nature—such as how successful different body plans were. The most important objective measure in
192-407: A character unique to a sub-set of the crown group. Furthermore, organisms in the stem group of a phylum can possess the "body plan" of the phylum without all the characteristics necessary to fall within it. This weakens the idea that each of the phyla represents a distinct body plan. A classification using this definition may be strongly affected by the chance survival of rare groups, which can make
240-485: A common ancestor . The terms flora (for plants), fauna (for animals), and, in the 21st century, funga (for fungi) are also used for life present in a particular region or time. When Carl Linnaeus introduced the rank-based system of nomenclature into biology in 1735, the highest rank was given the name "kingdom" and was followed by four other main or principal ranks: class , order , genus and species . Later two further main ranks were introduced, making
288-585: A distinct nucleus ( prokaryotes ) and organisms whose cells do have a distinct nucleus ( eukaryotes ). In 1937 Édouard Chatton 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 of prokaryotic organisms; as a revised phylum Monera of the Protista, it included organisms now classified as Bacteria and Archaea . Ernst Haeckel, in his 1904 book The Wonders of Life , had placed
336-402: A group ("a self-contained unity"): "perhaps such a real and completely self-contained unity is the aggregate of all species which have gradually evolved from one and the same common original form, as, for example, all vertebrates. We name this aggregate [a] Stamm [i.e., stock] ( Phylon )." In plant taxonomy , August W. Eichler (1883) classified plants into five groups named divisions,
384-602: A group containing Viridiplantae and the algal Rhodophyta and Glaucophyta divisions. The definition and classification of plants at the division level also varies from source to source, and has changed progressively in recent years. Thus some sources place horsetails in division Arthrophyta and ferns in division Monilophyta, while others place them both in Monilophyta, as shown below. The division Pinophyta may be used for all gymnosperms (i.e. including cycads, ginkgos and gnetophytes), or for conifers alone as below. Since
432-457: A middle undifferentiated layer called mesoglea, and radial symmetry. Some examples are corals , which are typically colonial; hydrae , jellyfish , sea anemones , and Aurelia , which are solitary; Pennatula ; Portuguese man o' war ; Gorgonia ; and Physalia . Coelenterata lack a specialized circulatory system, relying instead on diffusion across the tissue layers. All coelenterates are aquatic , mostly marine , animals. The body form
480-561: A parallel work, the Historia Plantarum , on plants. Carl Linnaeus (1707–1778) laid the foundations for modern biological nomenclature , now regulated by the Nomenclature Codes , in 1735. He distinguished two kingdoms of living things: Regnum Animale (' animal kingdom') and Regnum Vegetabile ('vegetable kingdom', for plants ). Linnaeus also included minerals in his classification system , placing them in
528-400: A phylum based on body plan has been proposed by paleontologists Graham Budd and Sören Jensen (as Haeckel had done a century earlier). The definition was posited because extinct organisms are hardest to classify: they can be offshoots that diverged from a phylum's line before the characters that define the modern phylum were all acquired. By Budd and Jensen's definition, a phylum is defined by
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#1732764731535576-471: A phylum much more diverse than it would be otherwise. Total numbers are estimates; figures from different authors vary wildly, not least because some are based on described species, some on extrapolations to numbers of undescribed species. For instance, around 25,000–27,000 species of nematodes have been described, while published estimates of the total number of nematode species include 10,000–20,000; 500,000; 10 million; and 100 million. The kingdom Plantae
624-706: A phylum, other phylum-level ranks appear, such as the case of Bacillariophyta (diatoms) within Ochrophyta . These differences became irrelevant after the adoption of a cladistic approach by the ISP, where taxonomic ranks are excluded from the classifications after being considered superfluous and unstable. Many authors prefer this usage, which lead to the Chromista-Protozoa scheme becoming obsolete. Currently there are 40 bacterial phyla (not including " Cyanobacteria ") that have been validly published according to
672-401: A set of characters shared by all its living representatives. This approach brings some small problems—for instance, ancestral characters common to most members of a phylum may have been lost by some members. Also, this definition is based on an arbitrary point of time: the present. However, as it is character based, it is easy to apply to the fossil record. A greater problem is that it relies on
720-401: A subjective decision about which groups of organisms should be considered as phyla. The approach is useful because it makes it easy to classify extinct organisms as " stem groups " to the phyla with which they bear the most resemblance, based only on the taxonomically important similarities. However, proving that a fossil belongs to the crown group of a phylum is difficult, as it must display
768-424: A term that remains in use today for groups of plants, algae and fungi. The definitions of zoological phyla have changed from their origins in the six Linnaean classes and the four embranchements of Georges Cuvier . Informally, phyla can be thought of as groupings of organisms based on general specialization of body plan . At its most basic, a phylum can be defined in two ways: as a group of organisms with
816-721: A third kingdom of life, the Protista , 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). Kingdom Protista or Protoctista Kingdom Plantae Kingdom Animalia Regnum Lapideum (minerals) The development of microscopy revealed important distinctions between those organisms whose cells do not have
864-615: A third kingdom, Regnum Lapideum . Regnum Animale (animals) Regnum Vegetabile ('vegetables'/plants) Regnum Lapideum (minerals) In 1674, Antonie van Leeuwenhoek , often called the "father of microscopy", sent the Royal Society 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
912-489: 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). Kingdom Monera Kingdom Protista or Protoctista Kingdom Plantae Kingdom Fungi Kingdom Animalia Kingdom Monera Kingdom Protista Kingdom Plantae Kingdom Fungi Kingdom Animalia In 1977, Carl Woese and colleagues proposed
960-485: Is radially symmetrical , diploblastic and does not have a coelom . The body has a single opening, the hypostome , surrounded by sensory tentacles equipped with either nematocysts or colloblasts to capture mostly planktonic prey. These tentacles are surrounded by a spacious cavity called the gastrovascular cavity , or coelenteron. Digestion is both intracellular and extracellular. Respiration and excretion are accomplished by simple diffusion. A network of nerves
1008-474: Is a paraphyletic taxon, which is less acceptable to present-day biologists than in the past. Proposals have been made to divide it among several new kingdoms, such as Protozoa and Chromista in the Cavalier-Smith system . Protist taxonomy has long been unstable, with different approaches and definitions resulting in many competing classification schemes. Many of the phyla listed below are used by
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#17327647315351056-563: Is commonly used in recent US high school biology textbooks, but has received criticism for compromising the current scientific consensus. 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 . Kingdom Eubacteria (Bacteria) Kingdom Archaebacteria (Archaea) Kingdom Protista or Protoctista Kingdom Plantae Kingdom Fungi Kingdom Animalia Thomas Cavalier-Smith supported
1104-405: Is defined in various ways by different biologists (see Current definitions of Plantae ). All definitions include the living embryophytes (land plants), to which may be added the two green algae divisions, Chlorophyta and Charophyta , to form the clade Viridiplantae . The table below follows the influential (though contentious) Cavalier-Smith system in equating "Plantae" with Archaeplastida ,
1152-481: Is generally included in kingdom Fungi, though its exact relations remain uncertain, and it is considered a protozoan by the International Society of Protistologists (see Protista , below). Molecular analysis of Zygomycota has found it to be polyphyletic (its members do not share an immediate ancestor), which is considered undesirable by many biologists. Accordingly, there is a proposal to abolish
1200-613: Is spread throughout the body. Many Cnidaria exhibit polymorphism , wherein different types of individuals are present in a colony for different functions. These individuals are called zooids . These animals generally reproduce asexually by budding, though sexual reproduction does occur in some groups. The scientific validity of the term coelenterate is currently rejected, as the Cnidaria and Ctenophora have less in common than previously assumed. Coelentera may only be monophyletic if both Placozoa and Bilateria are included. In particular,
1248-689: The Bacteriological Code Currently there are 2 phyla that have been validly published according to the Bacteriological Code Other phyla that have been proposed, but not validly named, include: Kingdom (biology) Traditionally, textbooks from Canada and the United States have used a system of six kingdoms ( Animalia , Plantae , Fungi , Protista , Archaea /Archaebacteria, and Bacteria or Eubacteria), while textbooks in other parts of
1296-565: The Catalogue of Life , and correspond to the Protozoa-Chromista scheme, with updates from the latest (2022) publication by Cavalier-Smith . Other phyla are used commonly by other authors, and are adapted from the system used by the International Society of Protistologists (ISP). Some of the descriptions are based on the 2019 revision of eukaryotes by the ISP. The number of protist phyla varies greatly from one classification to
1344-469: The two-empire system of prokaryotes and eukaryotes. The two-empire system would later be expanded to the three-domain system of Archaea, Bacteria, and Eukaryota. Kingdom Monera Kingdom Protista or Protoctista Kingdom Plantae Kingdom Animalia The differences between fungi 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
1392-497: The Zygomycota phylum. Its members would be divided between phylum Glomeromycota and four new subphyla incertae sedis (of uncertain placement): Entomophthoromycotina , Kickxellomycotina , Mucoromycotina , and Zoopagomycotina . Kingdom Protista (or Protoctista) is included in the traditional five- or six-kingdom model, where it can be defined as containing all eukaryotes that are not plants, animals, or fungi. Protista
1440-458: The above definitions is the "certain degree" that defines how different organisms need to be members of different phyla. The minimal requirement is that all organisms in a phylum should be clearly more closely related to one another than to any other group. Even this is problematic because the requirement depends on knowledge of organisms' relationships: as more data become available, particularly from molecular studies, we are better able to determine
1488-424: The additional rank branch (Latin: ramus ) can be inserted between subkingdom and infrakingdom, e.g., Protostomia and Deuterostomia in the classification of Cavalier-Smith. The classification of living things into animals and plants is an ancient one. Aristotle (384–322 BC) classified animal species in his History of Animals , while his pupil Theophrastus ( c. 371 – c. 287 BC ) wrote
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1536-521: 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 [had become] 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
1584-502: 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 and C. B. van Niel 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
1632-436: The consensus at that time, that the difference between Eubacteria and Archaebacteria 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 into two subkingdoms: Negibacteria ( Gram-negative bacteria ) and Posibacteria ( Gram-positive bacteria ). Technological advances in electron microscopy allowed
1680-507: The first publication of the APG system in 1998, which proposed a classification of angiosperms up to the level of orders , many sources have preferred to treat ranks higher than orders as informal clades. Where formal ranks have been provided, the traditional divisions listed below have been reduced to a very much lower level, e.g. subclasses . Wolf plants Hepatophyta Liver plants Coniferophyta Cone-bearing plant Phylum Microsporidia
1728-625: The fundamental subdivision of the prokaryotes into the Eubacteria (later called the Bacteria) and Archaebacteria (later called the Archaea), based on ribosomal RNA 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
1776-411: The next. The Catalogue of Life includes Rhodophyta and Glaucophyta in kingdom Plantae, but other systems consider these phyla part of Protista. In addition, less popular classification schemes unite Ochrophyta and Pseudofungi under one phylum, Gyrista , and all alveolates except ciliates in one phylum Myzozoa , later lowered in rank and included in a paraphyletic phylum Miozoa . Even within
1824-539: The other hand, the highly parasitic phylum Mesozoa was divided into two phyla ( Orthonectida and Rhombozoa ) when it was discovered the Orthonectida are probably deuterostomes and the Rhombozoa protostomes . This changeability of phyla has led some biologists to call for the concept of a phylum to be abandoned in favour of placing taxa in clades without any formal ranking of group size. A definition of
1872-443: The phylogenetic position of Ctenophora is controversial; it was first considered a sub-group of coelenterata but Hyman regarded it as a separate phylum. Most researchers think that Coelenterata is not monophyletic , and therefore any group containing Cnidaria and Ctenophora but excluding other phyla would be paraphyletic . Previously, some genomic studies have found support for monophyletic coelenterates. Despite this uncertainty,
1920-640: The plant kingdom Plantae contains about 14 phyla, and the fungus kingdom Fungi contains about 8 phyla. Current research in phylogenetics is uncovering the relationships among phyla within larger clades like Ecdysozoa and Embryophyta . The term phylum was coined in 1866 by Ernst Haeckel from the Greek phylon ( φῦλον , "race, stock"), related to phyle ( φυλή , "tribe, clan"). Haeckel noted that species constantly evolved into new species that seemed to retain few consistent features among themselves and therefore few features that distinguished them as
1968-475: The relationships between groups. So phyla can be merged or split if it becomes apparent that they are related to one another or not. For example, the bearded worms were described as a new phylum (the Pogonophora) in the middle of the 20th century, but molecular work almost half a century later found them to be a group of annelids , so the phyla were merged (the bearded worms are now an annelid family ). On
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2016-480: The result of the endosymbiosis of a proteobacterium , it was thought that these amitochondriate eukaryotes were primitively so, marking an important step in eukaryogenesis . As a result, these amitochondriate protists were separated from the protist kingdom, giving rise to the, at the same time, superkingdom and kingdom Archezoa . This superkingdom was opposed to the Metakaryota superkingdom, grouping together
2064-595: The separation of the Chromista from the Plantae kingdom. Indeed, the chloroplast of the chromists is located in the lumen of the endoplasmic reticulum instead of in the cytosol . Moreover, only chromists contain chlorophyll c . 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
2112-470: The sequence kingdom, phylum or division , class , order , family , genus and species . 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
2160-576: The term coelenterate is still used in informal settings to refer to the Cnidaria and Ctenophora. Complicating the issue is the 1997 work of Lynn Margulis (revising an earlier model by Thomas Cavalier-Smith ) that placed the Cnidaria and Ctenophora alone in the branch Radiata within Eumetazoa . (The latter refers to all the animals except the sponges and Placozoa ). Neither grouping is accepted universally, however, both are commonly encountered in taxonomic literature. Phylum In biology ,
2208-561: The two empire system. In the Whittaker system, Plantae included some algae. In other systems, such as Lynn Margulis 's system of five kingdoms, the plants included just the land plants ( Embryophyta ), 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
2256-463: The world, such as Bangladesh, Brazil, Greece, India, Pakistan, Spain, and the United Kingdom have used five kingdoms (Animalia, Plantae, Fungi, Protista and Monera ). Some recent classifications based on modern cladistics 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
2304-724: Was largely ignored in this separation by scientists of his time. Robert Whittaker recognized an additional kingdom for the Fungi . 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 ; his Plantae were mostly multicellular autotrophs , his Animalia multicellular heterotrophs , and his Fungi multicellular saprotrophs . The remaining two kingdoms, Protista and Monera, included unicellular and simple cellular colonies. The five kingdom system may be combined with
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