The hierarchy of biological classification's eight major taxonomic ranks. A kingdom contains one or more phyla. Intermediate minor rankings are not shown.

In biology, a phylum (əm/; plural: 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.[1][2][3] Depending on definitions, the animal kingdom Animalia or Metazoa contains approximately 35 phyla, the plant kingdom Plantae contains about 14, and the fungus kingdom Fungi contains about 8 phyla. Current research in phylogenetics is uncovering the relationships between phyla, which are contained in larger clades, like Ecdysozoa and Embryophyta.[citation needed]

General description

The term phylum was coined in 1866 by Ernst Haeckel from the Greek phylon (φῦλον, "race, stock"), related to phyle (φυλή, "tribe, clan").[4][5] 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 a group ("a self-contained unity"). "Wohl aber ist eine solche reale und vollkommen abgeschlossene Einheit die Summe aller Species, welche aus einer und derselben gemeinschaftlichen Stammform allmählig sich entwickelt haben, wie z. B. alle Wirbelthiere. Diese Summe nennen wir Stamm (Phylon)." which translates as: However, 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., race] (Phylon).) In plant taxonomy, August W. Eichler (1883) classified plants into five groups named divisions, a term that remains in use today for groups of plants, algae and fungi.[1][6] The definitions of zoological phyla have changed from their origins in the six Linnaean classes and the four embranchements of Georges Cuvier.[7]

Informally, phyla can be thought of as groupings of organisms based on general specialization of body plan.[8] At its most basic, a phylum can be defined in two ways: as a group of organisms with 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).[9] 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.[citation needed]

Definition based on genetic relation

The most important objective measure in the above definitions is the "certain degree" that defines how different organisms need to be 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.[9] 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 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).[10] On 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.[11]

This changeability of phyla has led some biologists to call for the concept of a phylum to be abandoned in favour of cladistics, a method in which groups are placed on a "family tree" without any formal ranking of group size.[9]

Definition based on body plan

A definition of 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 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 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.[9] However, proving that a fossil belongs to the crown group of a phylum is difficult, as it must display a character unique to a sub-set of the crown group.[9] 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.[12]

A classification using this definition may be strongly affected by the chance survival of rare groups, which can make a phylum much more diverse than it would be otherwise.[13]

Other Languages
Afrikaans: Filum
العربية: شعبة (تصنيف)
asturianu: Filu
Avañe'ẽ: Pehẽ'a
Bân-lâm-gú: Mn̂g (hun-lūi-ha̍k)
Basa Banyumasan: Filum
башҡортса: Тип (биология)
беларуская: Тып (біялогія)
беларуская (тарашкевіца)‎: Тып (біялёгія)
brezhoneg: Skourrad
català: Fílum
čeština: Kmen (biologie)
Cymraeg: Ffylwm
eesti: Hõimkond
Ελληνικά: Συνομοταξία
español: Filo
Esperanto: Filumo
euskara: Filum
Gaeilge: Fíleam
Gaelg: Phylum
galego: Filo
한국어: 문 (생물학)
Ilokano: Pilo
Bahasa Indonesia: Filum
italiano: Phylum
Basa Jawa: Filum
Kapampangan: Phylum (biolohia)
Kreyòl ayisyen: Filòm
ລາວ: ຟີລຳ
Lëtzebuergesch: Stamm (Biologie)
lietuvių: Tipas
മലയാളം: ഫൈലം
Malti: Phylum
Bahasa Melayu: Filum
Mìng-dĕ̤ng-ngṳ̄: Muòng (sĕng-ŭk-hŏk)
Nederlands: Stam (biologie)
日本語: 門 (分類学)
Napulitano: Phylum
norsk nynorsk: Biologisk rekkje
oʻzbekcha/ўзбекча: Tip (hayvonlar sistematikasi)
português: Filo
română: Încrengătură
Runa Simi: Rikch'aq putu
русиньскый: Тіп (біолоґія)
Scots: Phylum
Simple English: Phylum
slovenčina: Kmeň (taxonómia)
slovenščina: Deblo (taksonomija)
српски / srpski: Раздео
srpskohrvatski / српскохрватски: Koljeno (taksonomija)
suomi: Pääjakso
svenska: Fylum
Tagalog: Lapi
татарча/tatarça: Тип (биология)
ไทย: ไฟลัม
Türkçe: Şube
اردو: قسمہ
vèneto: Phylum
Tiếng Việt: Ngành (sinh học)
West-Vlams: Stamme (biologie)
Winaray: Phylum
中文: 门 (生物)