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Phylum

For other uses, see Phyla.

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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

Concepts of 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

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] Even this is problematic as the requirement depends on knowledge of organisms' relationships: As more data become 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 the 20th 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]

Definition based on body plan

A "body-plan" based definition of a phylum has been proposed by paleontologists Graham Budd and Sören Jensen. The definition was posited 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. 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 someTemplate:who 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

Animal phyla

Template:refimprove

Phylum Meaning Common name Distinguishing characteristic Species described
Acanthocephala Thorny headed worms Thorny-headed worms Reversible spiny proboscis that bears many rows of hooked spines Template:nts
Acoelomorpha Without gut Acoels No mouth or alimentary canal (alimentary canal = digestive tract in digestive system)
Annelida Little ring Segmented worms Multiple circular segment Template:nts+ extant
Arthropoda Jointed foot Arthropods Segmented bodies and jointed limbs, with Chitin exoskeleton Template:nts+
Brachiopoda Arm foot Lamp shells Lophophore and pedicle Template:nts-500 extant
Bryozoa Moss animals Moss animals, sea mats Lophophore, no pedicle, ciliated tentacles, anus outside ring of cilia Template:nts extant
Chaetognatha Longhair jaw Arrow worms Chitinous spines either side of head, fins Template:nts extant
Chordata With a cord Chordates Hollow dorsal nerve cord, notochord, pharyngeal slits, endostyle, post-anal tail Template:nts+
Cnidaria Stinging nettle Coelenterates Nematocysts (stinging cells) Template:nts
Ctenophora Comb bearer Comb jellies Eight "comb rows" of fused cilia Template:nts extant
Cycliophora Wheel carrying Symbion Circular mouth surrounded by small cilia, sac-like bodies Template:nts+
Echinodermata Spiny skin Echinoderms Fivefold radial symmetry in living forms, mesodermal calcified spines Template:nts extant; approx. 13,000 extinct
Entoprocta Inside anus Goblet worm Anus inside ring of cilia Template:nts
Gastrotricha Hair stomach Meiofauna Two terminal adhesive tubes Template:nts
Gnathostomulida Jaw orifice Jaw worms Template:nts
Hemichordata Half cord Acorn worms, pterobranchs Stomochord in collar, pharyngeal slits Template:nts extant
Kinorhyncha Motion snout Mud dragons Eleven segments, each with a dorsal plate Template:nts
Loricifera Corset bearer Brush heads Umbrella-like scales at each end Template:nts
Micrognathozoa Tiny jaw animals Accordion-like extensible thorax Template:nts
Mollusca Soft Mollusks / molluscs Muscular foot and mantle round shell Template:nts[12]
Nematoda Thread like Round worms Round cross section, keratin cuticle Template:nts–1,000,000
Nematomorpha Thread form Horsehair worms Template:nts
Nemertea A sea nymph Ribbon worms Template:nts
Onychophora Claw bearer Velvet worms Legs tipped by chitinous claws Template:nts extant
Orthonectida Straight swim Single layer of ciliated cells surrounding a mass of sex cells Template:nts
Phoronida Zeus's mistress Horseshoe worms U-shaped gut Template:nts
Placozoa Plate animals Template:nts
Platyhelminthes Flat worm Flatworms Template:nts[13]
Porifera* Pore bearer Sponges Perforated interior wall Template:nts+ extant
Priapulida Little Priapus
() Raplodrozoa Gill Knot Sugar Mold or Sweet Molds Coordinated growth of cell-cell communication must be assumed as it existed before multi-cellularity arose. Template:nts + extant
Rhombozoa Lozenge animal Single anteroposterior axial cell surrounded by ciliated cells Template:nts
Rotifera Wheel bearer Rotifers Anterior crown of cilia Template:nts
Sipuncula Small tube Peanut worms Mouth surrounded by invertible tentacles Template:nts–320
Tardigrada Slow step Water bears Four segmented body and head Template:nts+
Xenoturbellida Strange flatworm Ciliated deuterostome Template:nts
Total: 35 2,000,000+
Protostome Bilateria
Deuterostome
Basal/disputed
Others (Radiata or Parazoa)

Groups formerly ranked as phyla

Name as phylum Common name Current consensus
Aschelminthes Pseudocoelomates Divided into several pseudocoelomate phyla.
Craniata Subgroup of phylum Chordata; perhaps synonymous with Vertebrata.
Cephalochordata Lancelets Subphylum of phylum Chordata.
Cephalorhyncha Superphylum Scalidophora.
Coelenterata Divided into phyla Cnidaria and Ctenophora.
Echiura Spoon worms Class of phylum Annelida.
Enteropneusta Acorn worms Class of phylum Hemichordata.
Gephyra Peanut worms and spoon worms Divided into phyla Sipuncula and Echiura.
Mesozoa Mesozoans Divided into phyla Orthonectida and Rhombozoa.
Myxozoa Severely modified Cnidarians.
Pentastomida Tongue worms Subclass of Maxillopoda of phylum Arthropoda.
Pogonophora Beard worms Part of family Siboglinidae of phylum Annelida.
Pterobranchia Class of phylum Hemichordata.
Symplasma Glass sponges Class Hexactinellida of phylum Porifera.
Urochordata Tunicates Subphylum of phylum Chordata.
Vestimentifera Vent worms Part of family Siboglinidae of phylum Annelida.
Total: 16

Land plant divisions

Template:refimprove The ten Divisions into which plants, here defined as living (extant) land plants, may be placed are shown in the table below. This definition excludes the algal Divisions Chlorophyta and Charophyta which are included in the clade Viridiplantae (see also current definitions of Plantae). The definition and 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]

Division Meaning Common name Distinguishing characteristics
Anthocerotophyta[17] Anthoceros-like plants Hornworts Horn-shaped sporophytes, no vascular system
Bryophyta[18] Bryum-like plants, moss plants Mosses Persistent unbranched sporophytes, no vascular system
Marchantiophyta,[19]

Hepatophyta[18]

Marchantia-like plants

liver plants

Liverworts Ephemeral unbranched sporophytes, no vascular system
Lycopodiophyta,[20]

Lycophyta[21]

Lycopodium-like plants

"wolf" plants

Clubmosses & spikemosses Microphyll leaves, vascular system
Pteridophyta[citation needed] Pteris-like plants, fern plants Ferns & horsetails Prothallus gametophytes, vascular system
Pinophyta,[citation needed]

Coniferophyta[22]

Pinus-like plants

Cone-bearing plants

Conifers Cones containing seeds and wood composed of tracheids
Cycadophyta[23] Cycas-like plants, palm-like plants Cycads Seeds, crown of compound leaves
Ginkgophyta[24] Ginkgo-like plants Ginkgo, Maidenhair Seeds not protected by fruit (single living species)
Gnetophyta[25] Gnetum-like plants Gnetophytes Seeds and woody vascular system with vessels
Flowering plant

Anthophyta

flowering plants Flowering plants, angiosperms Flowers and fruit, vascular system with vessels
Total: 10

Fungal divisions

Phylum Meaning Common name Distinguishing characteristics
Chytridiomycota Little pot mushroom Chytrids Cellulose in cell walls, flagellated gametes
Deuteromycota Second mushroom Imperfect fungi Unclassified fungi; only asexual reproduction observed no other major distinguishments
Zygomycota Yolk mushroom Zygomycetes Blend gametangia to form a zygosporangium
Glomeromycota Ball mushroom None Form arbuscular mycorrhizae with plants
Ascomycota Bag/Wineskin Mushroom Sac fungi Produce spores in an 'ascus' which is a kind of fruiting bud
Basidiomycota Basidium Mushroom Club Fungi Produce spores from a 'basidium' which is a kind of fruiting bud
Total: 6

Protista phyla

Bacterial phyla/divisions

Script error: No such module "main". Currently there are 29 phyla accepted by LPSN[26]

  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

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

See also

Notes

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

References

  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. 7.0 7.1 7.2 7.3 7.4 Budd, G.E.; Jensen, S. (2000). "A critical reappraisal of the fossil record of the bilaterian phyla". Biological Reviews 75 (2): 253–295. PMID 10881389. doi:10.1111/j.1469-185X.1999.tb00046.x. 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. doi:10.1093/oxfordjournals.molbev.a025675. 
  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. JSTOR 1217531. doi:10.2307/1217531. 
  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. 18.0 18.1 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. JSTOR 1217531. doi:10.2307/1217531. 
  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. J.P. Euzéby. "List of Prokaryotic names with Standing in Nomenclature: Phyla". Retrieved 30 December 2010. 

External links