Phylum

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LifeDomainKingdomPhylumClassOrderFamilyGenusSpecies
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 (/ˈfləm/; plural: phyla)[note 1] is a taxonomic rank below kingdom and above class. Traditionally, in botany the term division is used instead of "phylum", although in 1993 the International Botanical Congress accepted the designation "phylum".[1][2] The kingdom Animalia contains approximately 35 phyla; the kingdom Plantae contains 12 phyla. Current research in phylogenetics is uncovering the relationships between phyla, which are contained in larger clades, like Ecdysozoa and Embryophyta.

General description and familiar examples[edit]

Concepts of animal phyla have changed importantly from their origins in the six Linnaean classes and the four "embranchements" of Georges Cuvier.[3] Haeckel introduced the term phylum, based on the Greek word phylon.[4] In plant taxonomy, Eichler (1883) classified all plants into five groups, named divisions. [5] Informally, phyla can be thought of as grouping organisms based on general specialization of body plan.[6] At the most basic level, 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).[7] Attempting to define a level of the Linnean hierarchy without referring to (evolutionary) relatedness is an unsatisfactory approach, but the phenetic definition is more useful when addressing questions of a morphological nature—such as how successful different body plans were.

Definition based on genetic relation[edit]

The largest objective measure in the above definitions is the "certain degree"—how unrelated do organisms need to be to be members of different phyla? The minimal requirement is that all organisms in a phylum should be related closely enough for them to be clearly more closely related to one another than to any other group.[7] However, even this is problematic, as the requirement depends on our current knowledge about organisms' relationships: As more data becomes available, particularly from molecular studies, we are better able to judge 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 XX century, but molecular work almost half a century later found them as a group of annelids and merged the phyla, so that the bearded worms are now an annelid family.[8] Likewise, 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.[9]

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.[7] So as to provide a handle on the size and significance of groups, a "body-plan" based definition of a phylum has been proposed by paleontologists Graham Budd and Sören Jensen. The definition was posited by paleontologists because extinct organisms are typically hardest to classify; they can be off-shoots that diverged from a phylum's line before the characters that define the modern phylum were all acquired.

Definition based on body plan[edit]

By Budd and Jensen's definition, phyla are defined by a set of characters shared by all their living representatives. This has a couple of small problems—for instance, characters common to most members of a phylum may be secondarily lost by some members. It is also defined 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 more major problem is that it relies on an objective decision of which group of organisms should be considered a phylum.

Its utility is that 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.[7] 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.[7] 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.[10]

Based upon this definition, which some say is unreasonably affected by the chance survival of rare groups, which vastly increase the size of phyla, representatives of many modern phyla did not appear until long after the Cambrian.[11]

Lists[edit]

Animal phyla[edit]

PhylumMeaningCommon nameDistinguishing characteristicSpecies described
AcanthocephalaThorny headed wormsThorny-headed wormsReversible spiny proboscis that bears many rows of hooked spinesapprox. 756
AcoelomorphaWithout gutAcoelsNo mouth or alimentary canal (alimentary canal = digestive tract in digestive system)
AnnelidaLittle ringSegmented wormsMultiple circular segment17,000+ extant
ArthropodaJointed footArthropodsSegmented bodies and jointed limbs, with Chitin exoskeleton1,134,000+
BrachiopodaArm footLamp shellsLophophore and pedicle300-500 extant
BryozoaMoss animalsMoss animals, sea matsLophophore, no pedicle, ciliated tentacles, anus outside ring of cilia5,000 extant
ChaetognathaLonghair jawArrow wormsChitinous spines either side of head, finsapprox. 100 extant
ChordataWith a cordChordatesHollow dorsal nerve cord, notochord, pharyngeal slits, endostyle, post-anal tailapprox. 100,000+
CnidariaStinging nettleCoelenteratesNematocysts (stinging cells)approx. 11,000
CtenophoraComb bearerComb jelliesEight "comb rows" of fused ciliaapprox. 100 extant
CycliophoraWheel carryingSymbionCircular mouth surrounded by small cilia, sac-like bodies3+
EchinodermataSpiny skinEchinodermsFivefold radial symmetry in living forms, mesodermal calcified spinesapprox. 7,000 extant; approx. 13,000 extinct
EntoproctaInside anusGoblet wormAnus inside ring of ciliaapprox. 150
GastrotrichaHair stomachMeiofaunaTwo terminal adhesive tubesapprox. 690
GnathostomulidaJaw orificeJaw wormsapprox. 100
HemichordataHalf cordAcorn worms, pterobranchsStomochord in collar, pharyngeal slitsapprox. 100 extant
KinorhynchaMotion snoutMud dragonsEleven segments, each with a dorsal plateapprox. 150
LoriciferaCorset bearerBrush headsUmbrella-like scales at each endapprox. 122
MicrognathozoaTiny jaw animalsAccordion-like extensible thorax1
MolluscaSoftMollusks / molluscsMuscular foot and mantle round shell112,000[12]
NematodaThread likeRound wormsRound cross section, keratin cuticle80,000–1,000,000
NematomorphaThread formHorsehair wormsapprox. 320
NemerteaA sea nymphRibbon wormsapprox. 1,200
OnychophoraClaw bearerVelvet wormsLegs tipped by chitinous clawsapprox. 200 extant
OrthonectidaStraight swimSingle layer of ciliated cells surrounding a mass of sex cellsapprox. 20
PhoronidaZeus's mistressHorseshoe wormsU-shaped gut11
PlacozoaPlate animals1
PlatyhelminthesFlat wormsFlat wormsapprox. 25,000[13]
Porifera*Pore bearerSpongesPerforated interior wall5,000+ extant
PriapulidaLittle Priapus16
RhombozoaLozenge animalSingle anteroposterior axial cell surrounded by ciliated cells75
RotiferaWheel bearerRotifersAnterior crown of ciliaapprox. 2,000
SipunculaSmall tubePeanut wormsMouth surrounded by invertible tentacles144–320
TardigradaSlow stepWater bearsFour segmented body and head1,000+
XenoturbellidaStrange flatwormCiliated deuterostome2
Total: 352,000,000+
ProtostomeBilateria
Deuterostome
Basal/disputed
Others (Radiata or Parazoa)

Groups formerly ranked as phyla[edit]

Name as phylumCommon nameCurrent consensus
AschelminthesPseudocoelomatesDivided into several pseudocoelomate phyla.
CraniataSubgroup of phylum Chordata; perhaps synonymous with Vertebrata.
CephalochordataLanceletsSubphylum of phylum Chordata.
CephalorhynchaSuperphylum Scalidophora.
CoelenterataDivided into phyla Cnidaria and Ctenophora.
EchiuraSpoon wormsClass of phylum Annelida.
EnteropneustaAcorn wormsClass of phylum Hemichordata.
GephyraPeanut worms and spoon wormsDivided into phyla Sipuncula and Echiura.
MesozoaMesozoansDivided into phyla Orthonectida and Rhombozoa.
MyxozoaSeverely modified Cnidarians.
PentastomidaTongue wormsSubclass of Maxillopoda of phylum Arthropoda.
PogonophoraBeard wormsPart of family Siboglinidae of phylum Annelida.
PterobranchiaClass of phylum Hemichordata.
SymplasmaGlass spongesClass Hexactinellida of phylum Porifera.
UrochordataTunicatesSubphylum of phylum Chordata.
VestimentiferaVent wormsPart of family Siboglinidae of phylum Annelida.

Plant divisions[edit]

Divisions into which living (extant) plants may be placed are shown in the table below. The classification of plants at this level varies from source to source. Thus some sources place horsetails in division Arthrophyta and ferns in division Pteridophyta,[14] while others place them both in Pteridophyta, as shown below. The division Pinophyta may be used for all gymnosperms (i.e. including cycads, ginkgos and gnetophytes),[15] or for conifers alone as below.

Since the first publication of the APG system in 1998, which proposed a classification of angiosperms 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.[16]

DivisionMeaningCommon nameDistinguishing characteristics
Anthocerotophyta[17]Anthoceros-like plantsHornwortsHorn-shaped sporophytes, no vascular system
Bryophyta[18]Bryum-like plants, moss plantsMossesPersistent unbranched sporophytes, no vascular system
Marchantiophyta,[19]

Hepatophyta[18]

Marchantia-like plants

liver plants

LiverwortsEphemeral unbranched sporophytes, no vascular system
Lycopodiophyta,[20]

Lycophyta[21]

Lycopodium-like plants

"wolf" plants

Clubmosses & spikemossesMicrophyll leaves, vascular system
Pteridophyta[citation needed]Pteris-like plants, fern plantsFerns & horsetailsProthallus gametophytes, vascular system
Pinophyta,[citation needed]

Coniferophyta[22]

Pinus-like plants

Cone-bearing plants

ConifersCones containing seeds and wood composed of tracheids
Cycadophyta[23]Cycas-like plants, palm-like plantsCycadsSeeds, crown of compound leaves
Ginkgophyta[24]Ginkgo-like plantsGinkgo, MaidenhairSeeds not protected by fruit (single living species)
Gnetophyta[25]Gnetum-like plantsGnetophytesSeeds and woody vascular system with vessels
Magnoliophyta,[26]

Anthophyta[citation needed]

Magnolia-like plants

flower plants

Flowering plants, angiospermsFlowers and fruit, vascular system with vessels

Fungal divisions[edit]

PhylumMeaningCommon nameDistinguishing characteristics
ChytridiomycotaLittle pot mushroomChytridsCellulose in cell walls, flagellated gametes
DeuteromycotaSecond mushroomImperfect fungiUnclassified fungi; only asexual reproduction observed no other major distinguishments
ZygomycotaYolk mushroomZygomycetesBlend gametangia to form a zygosporangium
GlomeromycotaBall mushroomNoneForm arbuscular mycorrhizae with plants
AscomycotaBag/Wineskin MushroomSac fungiProduce spores in an 'ascus'which is a kind of fruiting bud
BasidiomycotaBasidium MushroomClub FungiProduce spores from a 'basidium' which is a kind of fruiting bud

Protista phyla[edit]

Bacterial Phyla/Divisions[edit]

Currently there are 29 phyla accepted by LPSN[27]

  1. Acidobacteria, phenotipically diverse and mostly uncultured
  2. Actinobacteria, High-G+C Gram positive species
  3. Aquificae, only 14 thermophilic genera, deep branching
  4. Bacteroidetes
  5. Caldiserica, formerly candidate division OP5, Caldisericum exile is the sole representative
  6. Chlamydiae, only 6 genera
  7. Chlorobi, only 7 genera
  8. Chloroflexi,
  9. Chrysiogenetes, only 3 genera (Chrysiogenes arsenatis, Desulfurispira natronophila, Desulfurispirillum alkaliphilum)
  10. Cyanobacteria, also known as the blue-green algae
  11. Deferribacteres
  12. Deinococcus-Thermus, Deinococcus radiodurans and Thermus aquaticus are "commonly known" species of this phyla
  13. Dictyoglomi
  14. Elusimicrobia, formerly candidate division Thermite Group 1
  15. Fibrobacteres
  16. Firmicutes, Low-G+C Gram positive species, such as the spore-formers Bacilli (aerobic) and Clostridia (anaerobic)
  17. Fusobacteria
  18. Gemmatimonadetes
  19. Lentisphaerae, formerly clade VadinBE97
  20. Nitrospira
  21. Planctomycetes
  22. Proteobacteria, the most known phyla, containing species such as Escherichia coli or Pseudomonas aeruginosa
  23. Spirochaetes, species include Borrelia burgdorferi, which causes Lyme disease
  24. Synergistetes
  25. Tenericutes, alternatively class Mollicutes in phylum Firmicutes (notable genus: Mycoplasma)
  26. Thermodesulfobacteria
  27. Thermomicrobia
  28. Thermotogae, deep branching
  29. Verrucomicrobia

Archaeal Phyla/Division/Kingdoms[edit]

  1. Crenarchaeota, Second most common archaeal phylum
  2. Euryarchaeota, most common archaeal phylum
  3. Korarchaeota
  4. Nanoarchaeota, ultra-small symbiotes
  5. Thaumarchaeota

See also[edit]

Notes[edit]

  1. ^ The term was coined by Haeckel from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan."

References[edit]

  1. ^ "Life sciences". The American Heritage New Dictionary of Cultural Literacy (third ed.). Houghton Mifflin Company. 2005. Retrieved 2008-10-04. "Phyla in the plant kingdom are frequently called divisions." 
  2. ^ Berg, Linda R. (2007-03-02). Introductory Botany: Plants, People, and the Environment (2 ed.). Cengage Learning. p. 15. ISBN 9780534466695. Retrieved 23 July 2012. 
  3. ^ Collins AG, Valentine JW (2001). "Defining phyla: evolutionary pathways to metazoan body plans." Evol. Dev. 3: 432-442.
  4. ^ Valentine 2004, p. 8.
  5. ^ Naik, V. N. (1984). Taxonomy of Angiosperms. Tata McGraw Hill, New Delhi, p. 27.
  6. ^ Valentine, James W. (2004). On the Origin of Phyla. Chicago: University Of Chicago Press. p. 7. ISBN 0-226-84548-6.  "Classifications of organisms in hierarchical systems were in use by the seventeenth and eighteenth centuries. Usually organisms were grouped according to their what? morphological similarities as perceived by those early workers, and those groups were then grouped according to their similarities, and so on, to form a hierarchy."
  7. ^ a b c d e Budd, G.E.; Jensen, S. (2000). "A critical reappraisal of the fossil record of the bilaterian phyla". Biological Reviews 75 (2): 253–295. doi:10.1111/j.1469-185X.1999.tb00046.x. PMID 10881389. Retrieved 2007-05-26. 
  8. ^ Rouse G.W. (2001). "A cladistic analysis of Siboglinidae Caullery, 1914 (Polychaeta, Annelida): formerly the phyla Pogonophora and Vestimentifera". Zoological Journal of the Linnean Society 132 (1): 55–80. doi:10.1006/zjls.2000.0263. 
  9. ^ Pawlowski J, Montoya-Burgos JI, Fahrni JF, Wüest J, Zaninetti L (October 1996). "Origin of the Mesozoa inferred from 18S rRNA gene sequences". Mol. Biol. Evol. 13 (8): 1128–32. PMID 8865666. 
  10. ^ Budd, G.E. (1998). "Arthropod body-plan evolution in the Cambrian with an example from anomalocaridid muscle". Lethaia (Blackwell Synergy) 31 (3): 197–210. doi:10.1111/j.1502-3931.1998.tb00508.x. 
  11. ^ Briggs, D. E. G; Fortey, R. A (2005). "Wonderful strife: systematics, stem groups, and the phylogenetic signal of the Cambrian radiation". Paleobiology 31 (2 (Suppl)): 94–112. doi:10.1666/0094-8373(2005)031[0094:WSSSGA]2.0.CO;2. 
  12. ^ Feldkamp, S. (2002) Modern Biology. Holt, Rinehart, and Winston, USA. (pp. 725)
  13. ^ Species Register. "Flatworms — Phylum Platyhelminthes". Marine Discovery Centres. Retrieved 2007-04-09. 
  14. ^ Mauseth 2012, pp. 514, 517.
  15. ^ Cronquist, A.; A. Takhtajan, W. Zimmermann (1966). "On the higher taxa of Embryobionta". Taxon (International Association for Plant Taxonomy (IAPT)) 15 (15): 129–134. doi:10.2307/1217531. JSTOR 1217531. 
  16. ^ Chase, Mark W. & Reveal, James L. (2009), "A phylogenetic classification of the land plants to accompany APG III", Botanical Journal of the Linnean Society 161 (2): 122–127, doi:10.1111/j.1095-8339.2009.01002.x 
  17. ^ Mauseth, James D. (2012). Botany : An Introduction to Plant Biology (5th ed.). Sudbury, MA: Jones and Bartlett Learning. ISBN 978-1-4496-6580-7.  p. 489
  18. ^ a b Mauseth 2012, p. 489.
  19. ^ Crandall-Stotler, Barbara; Stotler, Raymond E. (2000). "Morphology and classification of the Marchantiophyta". In A. Jonathan Shaw & Bernard Goffinet (Eds.). Bryophyte Biology. Cambridge: Cambridge University Press. p. 21. ISBN 0-521-66097-1. 
  20. ^ Cronquist, A.; A. Takhtajan, W. Zimmermann (1966). "On the higher taxa of Embryobionta". Taxon (International Association for Plant Taxonomy (IAPT)) 15 (15): 129–134. doi:10.2307/1217531. JSTOR 1217531. 
  21. ^ Mauseth 2012, p. 509.
  22. ^ Mauseth 2012, p. 535.
  23. ^ Mauseth 2012, p. 540.
  24. ^ Mauseth 2012, p. 542.
  25. ^ Mauseth 2012, p. 543.
  26. ^ Mauseth 2012, p. 547.
  27. ^ J.P. Euzéby. "List of Prokaryotic names with Standing in Nomenclature: Phyla". Retrieved 30 December 2010. 

External links[edit]