Phylum

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For other uses, see Phyla.
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 (/ˈfaɪləm/; plural: phyla)[note 1] is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division.[1] The kingdom Animalia contains approximately 35 phyla; the kingdom Plantae contains 12 divisions. 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

Informally, phyla can be thought of as grouping organisms based on general specialization of body plan,[2] 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).[3] 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.[3] 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) when described in 1914, but molecular work almost a century later found them closely related to annelids and merged the phyla, so that the bearded worms are now an annelid family.[4] Likewise, the highly parasitic phylum Mesozoa was divided into two phyla Orthonectida and Rhombozoa, when it was discovered the Orthonectida are deuterostomes and the Rhombozoa protostomes.[5]

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 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

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.[3] 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.[3] 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.[6]

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.[7]

Lists

Animal phyla

Phylum Meaning Common name Distinguishing characteristic Species described
Acanthocephala Thorny headed worms Thorny-headed worms Reversible spiny proboscis approx. 756
Acoelomorpha Without gut Acoels No mouth or alimentary canal (alimentary canal = digestive tract in digestive system)
Annelida Little ring Segmented worms Multiple circular segment 17,000+ extant
Arthropoda Jointed foot Arthropods Chitin exoskeleton 1,134,000+
Brachiopoda Arm foot Lamp shells Lophophore and pedicle 300-500 extant
Bryozoa Moss animals Moss animals, sea mats Lophophore, no pedicle, ciliated tentacles 5,000 extant
Chaetognatha Longhair jaw Arrow worms Chitinous spines either side of head, fins approx. 100 extant
Chordata Cord Chordates Hollow dorsal nerve cord, notochord, pharyngeal slits, endostyle, post-anal tail approx. 100,000+
Cnidaria Stinging nettle Coelenterates Nematocysts (stinging cells) approx. 11,000
Ctenophora Comb bearer Comb jellies Eight "comb rows" of fused cilia approx. 100 extant
Cycliophora Wheel carrying Symbion Circular mouth surrounded by small cilia 3+
Echinodermata Spiny skin Echinoderms Fivefold radial symmetry in living forms, mesodermal calcified spines approx. 7,000 extant; approx. 13,000 extinct
Entoprocta Inside anus Goblet worm Anus inside ring of cilia approx. 150
Gastrotricha Hair stomach Meiofauna Two terminal adhesive tubes approx. 690
Gnathostomulida Jaw orifice Jaw worms approx. 100
Hemichordata Half cord Acorn worms, pterobranchs Stomochord in collar, pharyngeal slits approx. 100 extant
Kinorhyncha Motion snout Mud dragons Eleven segments, each with a dorsal plate approx. 150
Loricifera Corset bearer Brush heads Umbrella-like scales at each end approx. 122
Micrognathozoa Tiny jaw animals — Accordion like extensible thorax 1
Mollusca Soft Mollusks / molluscs Muscular foot and mantle round shell 112,000[8]
Nematoda Thread like Round worms Round cross section, keratin cuticle 80,000–1,000,000
Nematomorpha Thread form Horsehair worms approx. 320
Nemertea A sea nymph Ribbon worms approx. 1,200
Onychophora Claw bearer Velvet worms Legs tipped by chitinous claws approx. 200 extant
Orthonectida Straight swim Single layer of ciliated cells surrounding a mass of sex cells approx. 20
Phoronida Zeus's mistress Horseshoe worms U-shaped gut 20
Placozoa Plate animals 1
Platyhelminthes Flat worms Flat worms approx. 25,000[9]
Porifera* Pore bearer Sponges Perforated interior wall 5,000+ extant
Priapulida Little Priapus 16
Rhombozoa Lozenge animal — Single axial cell surrounded by ciliated cells 75
Rotifera Wheel bearer Rotifers Anterior crown of cilia approx. 2,000
Sipuncula Small tube Peanut worms Mouth surrounded by invertible tentacles 144–320
Tardigrada Slow step Water bears Four segmented body and head 1,000+
Xenoturbellida Strange flatworm — Ciliated deuterostome 2
Total: 35 2,000,000-
Protostome Bilateria
Deuterostome
Basal/disputed
Other

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.
Echiura Spoon worms Class of phylum Annelida.
Enterepneusta 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.

Plant divisions

Division Meaning Common name Distinguishing characteristics
Anthocerotophyta Flower-horn plants Hornworts Horn-shaped sporophytes, no vascular system
Bryophyta Moss plants Mosses Persistent unbranched sporophytes, no vascular system
Marchantiophyta Marchantia plants Liverworts Ephemeral unbranched sporophytes, no vascular system
Lycopodiophyta Wolf foot plants Clubmosses & Spikemosses Microphyll leaves, vascular system
Pteridophyta Fern plants Ferns & Horsetails Prothallus gametophytes, vascular system
Pteridospermatophyta Fern with seeds plant Seed ferns Only known from fossils, mostly Devonian, ranking in dispute[10]
Coniferophyta Sap/pitch plants Conifers Cones containing seeds and wood composed of tracheids
Cycadophyta Palm plants Cycads Seeds, crown of compound leaves
Ginkgophyta Ginkgo plants Ginkgo, Maidenhair Seeds not protected by fruit (single species)
Gnetophyta Gnetophytes Seeds and woody vascular system with vessels
Anthophyta (or Magnoliophyta)  Flower plant Flowering plants Flowers and fruit, vascular system with vessels

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
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'
Basidiomycota Basidium Mushroom Club Fungi Produce spores from a 'basidium'

Bacterial Phyla/Divisions

Main article: Bacterial phyla

Currently there are 29 phyla accepted by LPSN[11]

  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 ANo ito?
  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

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

See also

Notes

  1. ^ The term was coined by Georges Cuvier 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 4 October 2008. Phyla in the plant kingdom are frequently called divisions.
  2. ^ 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."
  3. ^ a b c d Budd, G.E. (2000). "A critical reappraisal of the fossil record of the bilaterian phyla". Biological Reviews. 75 (2): 253–295. doi:10.1017/S000632310000548X. PMID 10881389. Retrieved 26 May 2007. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  4. ^ 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.
  5. ^ Pawlowski J, Montoya-Burgos JI, Fahrni JF, Wüest J, Zaninetti L (1996). "Origin of the Mesozoa inferred from 18S rRNA gene sequences". Mol. Biol. Evol. 13 (8): 1128–32. PMID 8865666. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  6. ^ Budd, G.E. (1998). "Arthropod body-plan evolution in the Cambrian with an example from anomalocaridid muscle". Lethaia. 31 (3). Blackwell Synergy: 197–210. doi:10.1111/j.1502-3931.1998.tb00508.x.
  7. ^ 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.
  8. ^ Feldkamp, S. (2002) Modern Biology. Holt, Rinehart, and Winston, USA. (pp. 725)
  9. ^ Species Register. "Flatworms — Phylum Platyhelminthes". Marine Discovery Centres. Retrieved 9 April 2007. {{cite web}}: Cite has empty unknown parameter: |coauthors= (help)
  10. ^ ""Kingdom Plantae Tree of Life"".
  11. ^ J.P. Euzéby. "List of Prokaryotic names with Standing in Nomenclature: Phyla". Retrieved 30 December 2010.

External links

Look up Phylum in Wiktionary, the free dictionary.

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