Phylum
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
This section needs additional citations for verification. (July 2011) |
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
Currently there are 29 phyla accepted by LPSN[11]
- Acidobacteria, phenotipically diverse and mostly uncultured
- Actinobacteria, High-G+C Gram positive species
- Aquificae, only 14 thermophilic genera, deep branching
- Bacteroidetes
- Caldiserica, formerly candidate division OP5, Caldisericum exile is the sole representative
- Chlamydiae, only 6 genera
- Chlorobi, only 7 genera
- Chloroflexi,
- Chrysiogenetes, only 3 genera (Chrysiogenes arsenatis, Desulfurispira natronophila, Desulfurispirillum alkaliphilum)
- Cyanobacteria, also known as the blue-green algae
- Deferribacteres
- Deinococcus-Thermus, Deinococcus radiodurans and Thermus aquaticus are "commonly known" species of this phyla
- Dictyoglomi
- Elusimicrobia, formerly candidate division Thermite Group 1
- Fibrobacteres
- Firmicutes, Low-G+C Gram positive species, such as the spore-formers Bacilli (aerobic) and Clostridia (anaerobic)
- Fusobacteria
- Gemmatimonadetes
- Lentisphaerae, formerly clade VadinBE97
- Nitrospira
- Planctomycetes ANo ito?
- Proteobacteria, the most known phyla, containing species such as Escherichia coli or Pseudomonas aeruginosa
- Spirochaetes, species include Borrelia burgdorferi, which causes Lyme disease
- Synergistetes
- Tenericutes, alternatively class Mollicutes in phylum Firmicutes (notable genus: Mycoplasma)
- Thermodesulfobacteria
- Thermomicrobia
- Thermotogae, deep branching
- Verrucomicrobia
Archaeal Phyla/Division
- Crenarchaeota, Second most common archaeal phylum
- Euryarchaeota, most common archaeal phylum
- Korarchaeota
- Nanoarchaeota, ultra-small symbiotes
- Thaumarchaeota
See also
Notes
- ^ The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan."
References
- ^ "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.
- ^ 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."
- ^ 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.
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suggested) (help) - ^ 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.
- ^ 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.
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ignored (help)CS1 maint: multiple names: authors list (link) - ^ 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.
- ^ 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.
- ^ Feldkamp, S. (2002) Modern Biology. Holt, Rinehart, and Winston, USA. (pp. 725)
- ^ Species Register. "Flatworms — Phylum Platyhelminthes". Marine Discovery Centres. Retrieved 9 April 2007.
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(help) - ^ ""Kingdom Plantae Tree of Life"".
- ^ J.P. Euzéby. "List of Prokaryotic names with Standing in Nomenclature: Phyla". Retrieved 30 December 2010.
External links
- Are phyla "real"? Is there really a well-defined "number of animal phyla" extant and in the fossil record?
- Major Phyla Of Animals