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For other uses, see Phyla. Phylum_sentence_0

In biology, a phylum (/ˈfaɪləm/; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Phylum_sentence_1

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. Phylum_sentence_2

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. Phylum_sentence_3

Current research in phylogenetics is uncovering the relationships between phyla, which are contained in larger clades, like Ecdysozoa and Embryophyta. Phylum_sentence_4

General description Phylum_section_0

The term phylum was coined in 1866 by Ernst Haeckel from the Greek phylon (, "race, stock"), related to phyle (, "tribe, clan"). Phylum_sentence_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"). Phylum_sentence_6

"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. Phylum_sentence_7

B. alle Wirbelthiere. Phylum_sentence_8

Diese Summe nennen wir Stamm (Phylon)." Phylum_sentence_9

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. Phylum_sentence_10

We name this aggregate [a] Stamm [i.e., race] (Phylon). Phylum_sentence_11

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. Phylum_sentence_12

The definitions of zoological phyla have changed from their origins in the six Linnaean classes and the four embranchements of Georges Cuvier. Phylum_sentence_13

Informally, phyla can be thought of as groupings of organisms based on general specialization of body plan. Phylum_sentence_14

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). Phylum_sentence_15

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. Phylum_sentence_16

Definition based on genetic relation Phylum_section_1

The most important objective measure in the above definitions is the "certain degree" that defines how different organisms need to be members of different phyla. Phylum_sentence_17

The minimal requirement is that all organisms in a phylum should be clearly more closely related to one another than to any other group. Phylum_sentence_18

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. Phylum_sentence_19

So phyla can be merged or split if it becomes apparent that they are related to one another or not. Phylum_sentence_20

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). Phylum_sentence_21

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. Phylum_sentence_22

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. Phylum_sentence_23

Definition based on body plan Phylum_section_2

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). Phylum_sentence_24

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. Phylum_sentence_25

By Budd and Jensen's definition, a phylum is defined by a set of characters shared by all its living representatives. Phylum_sentence_26

This approach brings some small problems—for instance, ancestral characters common to most members of a phylum may have been lost by some members. Phylum_sentence_27

Also, this definition is based on an arbitrary point of time: the present. Phylum_sentence_28

However, as it is character based, it is easy to apply to the fossil record. Phylum_sentence_29

A greater problem is that it relies on a subjective decision about which groups of organisms should be considered as phyla. Phylum_sentence_30

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. Phylum_sentence_31

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. Phylum_sentence_32

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. Phylum_sentence_33

This weakens the idea that each of the phyla represents a distinct body plan. Phylum_sentence_34

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. Phylum_sentence_35

Known phyla Phylum_section_3

Animals Phylum_section_4

Main article: Animal Phylum_sentence_36

Plants Phylum_section_5

Main article: Plant Phylum_sentence_37

The kingdom Plantae is defined in various ways by different biologists (see Current definitions of Plantae). Phylum_sentence_38

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. Phylum_sentence_39

The table below follows the influential (though contentious) Cavalier-Smith system in equating "Plantae" with Archaeplastida, a group containing Viridiplantae and the algal Rhodophyta and Glaucophyta divisions. Phylum_sentence_40

The definition and classification of plants at the division level also varies from source to source, and has changed progressively in recent years. Phylum_sentence_41

Thus some sources place horsetails in division Arthrophyta and ferns in division Pteridophyta, while others place them both in Pteridophyta, as shown below. Phylum_sentence_42

The division Pinophyta may be used for all gymnosperms (i.e. including cycads, ginkgos and gnetophytes), or for conifers alone as below. Phylum_sentence_43

Since 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. Phylum_sentence_44

Where formal ranks have been provided, the traditional divisions listed below have been reduced to a very much lower level, e.g. subclasses. Phylum_sentence_45


Phylum_cell_0_0_0 Land plantsPhylum_cell_0_0_1 ViridiplantaePhylum_cell_0_0_2
Phylum_cell_0_1_0 Green algaePhylum_cell_0_1_1
Phylum_cell_0_2_0 Other algae (Biliphyta)Phylum_cell_0_2_1

Fungi Phylum_section_6

Main article: Fungi Phylum_sentence_46

Phylum Microsporidia 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). Phylum_sentence_47

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. Phylum_sentence_48

Accordingly, there is a proposal to abolish the Zygomycota phylum. Phylum_sentence_49

Its members would be divided between phylum Glomeromycota and four new subphyla incertae sedis (of uncertain placement): Entomophthoromycotina, Kickxellomycotina, Mucoromycotina, and Zoopagomycotina. Phylum_sentence_50

Protista Phylum_section_7

Main article: Protista taxonomy Phylum_sentence_51

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. Phylum_sentence_52

Protista is a polyphyletic taxon (it includes groups not directly related to one another), which is less acceptable to present-day biologists than in the past. Phylum_sentence_53

Proposals have been made to divide it among several new kingdoms, such as Protozoa and Chromista in the Cavalier-Smith system. Phylum_sentence_54

Protist taxonomy has long been unstable, with different approaches and definitions resulting in many competing classification schemes. Phylum_sentence_55

The phyla listed here are used for Chromista and Protozoa by the Catalogue of Life, adapted from the system used by the International Society of Protistologists. Phylum_sentence_56


Phylum_cell_1_0_0 HarosaPhylum_cell_1_0_1
Phylum_cell_1_1_0 ProtozoaPhylum_cell_1_1_1

The Catalogue of Life includes Rhodophyta and Glaucophyta in kingdom Plantae, but other systems consider these phyla part of Protista. Phylum_sentence_57

Bacteria Phylum_section_8

Main article: Bacterial phyla Phylum_sentence_58

Currently there are 29 phyla accepted by List of Prokaryotic names with Standing in Nomenclature (LPSN) Phylum_sentence_59


  1. Acidobacteria, phenotypically diverse and mostly unculturedPhylum_item_0_0
  2. Actinobacteria, High-G+C Gram positive speciesPhylum_item_0_1
  3. Aquificae, only 14 thermophilic genera, deep branchingPhylum_item_0_2
  4. ArmatimonadetesPhylum_item_0_3
  5. BacteroidetesPhylum_item_0_4
  6. Caldiserica, formerly candidate division OP5, Caldisericum exile is the sole representativePhylum_item_0_5
  7. Chlamydiae, only 6 generaPhylum_item_0_6
  8. Chlorobi, only 7 genera, green sulphur bacteriaPhylum_item_0_7
  9. Chloroflexi, green non-sulphur bacteriaPhylum_item_0_8
  10. Chrysiogenetes, only 3 genera (Chrysiogenes arsenatis, Desulfurispira natronophila, Desulfurispirillum alkaliphilum)Phylum_item_0_9
  11. Cyanobacteria, also known as the blue-green algaePhylum_item_0_10
  12. DeferribacteresPhylum_item_0_11
  13. Deinococcus-Thermus, Deinococcus radiodurans and Thermus aquaticus are "commonly known" species of this phylaPhylum_item_0_12
  14. DictyoglomiPhylum_item_0_13
  15. Elusimicrobia, formerly candidate division Thermite Group 1Phylum_item_0_14
  16. FibrobacteresPhylum_item_0_15
  17. Firmicutes, Low-G+C Gram positive species, such as the spore-formers Bacilli (aerobic) and Clostridia (anaerobic)Phylum_item_0_16
  18. FusobacteriaPhylum_item_0_17
  19. GemmatimonadetesPhylum_item_0_18
  20. Lentisphaerae, formerly clade VadinBE97Phylum_item_0_19
  21. NitrospiraPhylum_item_0_20
  22. PlanctomycetesPhylum_item_0_21
  23. Proteobacteria, the most known phyla, containing species such as Escherichia coli or Pseudomonas aeruginosaPhylum_item_0_22
  24. Spirochaetes, species include Borrelia burgdorferi, which causes Lyme diseasePhylum_item_0_23
  25. SynergistetesPhylum_item_0_24
  26. Tenericutes, alternatively class Mollicutes in phylum Firmicutes (notable genus: Mycoplasma)Phylum_item_0_25
  27. ThermodesulfobacteriaPhylum_item_0_26
  28. Thermotogae, deep branchingPhylum_item_0_27
  29. VerrucomicrobiaPhylum_item_0_28

Archaea Phylum_section_9

Main article: Archaea Phylum_sentence_60

Currently there are five phyla accepted by List of Prokaryotic names with Standing in Nomenclature (LPSN). Phylum_sentence_61


  1. Crenarchaeota, second most common archaeal phylumPhylum_item_1_29
  2. Euryarchaeota, most common archaeal phylumPhylum_item_1_30
  3. KorarchaeotaPhylum_item_1_31
  4. Nanoarchaeota, ultra-small symbiotes, single known speciesPhylum_item_1_32
  5. ThaumarchaeotaPhylum_item_1_33

See also Phylum_section_10


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