In biology, a PHYLUM (/ˈfaɪləm/ ; plural : PHYLA) is a level of
classification or taxonomic rank below Kingdom and above Class .
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. Depending on
definitions, the animal kingdom
Animalia or Metazoa contains
approximately 35 phyla, the plant kingdom
Plantae contains about 12,
and the fungus kingdom
* 1 General description and familiar examples
* 1.1 Definition based on genetic relation * 1.2 Definition based on body plan
* 2 Known phyla
* 3 See also * 4 Notes * 5 References * 6 External links
GENERAL DESCRIPTION AND FAMILIAR EXAMPLES
The term phylum was coined by Haeckel from the Greek φῦλον
_phylon_, "race, stock," related to φυλή _phyle_, "tribe, clan."
In plant taxonomy,
Eichler (1883) classified plants into five groups
named divisions, a term that remains in use today for groups of
plants, algae and fungi. The definitions of zoological phyla have
changed from their origins in the six Linnaean classes and the four
Informally, phyla can be thought of as groupings of organisms based on general specialization of body plan . 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). 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.
DEFINITION BASED ON GENETIC RELATION
The most important objective measure in the above definitions is the "certain degree" that defines how different organisms need to be to be members of different phyla? The minimal requirement is that all organisms in a phylum should be clearly more closely related to one another than to any other group. 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. 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 to be a group of annelids , so the phyla were merged (the bearded worms are now an annelid family ). 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 .
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.
DEFINITION BASED ON BODY PLAN
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). 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. By Budd and Jensen's definition, a phylum is defined by a set of characters shared by all its living representatives.
This approach brings some small problems—for instance, ancestral characters common to most members of a phylum may have been lost by some members. Also, this definition is 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 greater problem is that it relies on a subjective decision about which groups of organisms should be considered as phyla.
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. 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. 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.
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. Representatives of many modern phyla did not appear until long _after_ the Cambrian.
_ This section NEEDS ADDITIONAL CITATIONS FOR VERIFICATION . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed. (February 2013)_ _(Learn how and when to remove this template message )_
Others (Radiata or Parazoa)
PHYLUM MEANING COMMON NAME DISTINGUISHING CHARACTERISTIC SPECIES DESCRIBED
Acanthocephala Thorny head Thorny-headed worms :278 Reversible spiny proboscis that bears many rows of hooked spines 7003110000000000000♠approx. 1,100
Annelida Little ring :306 Annelids Multiple circular segment 7004170000000000000♠17,000+ extant
Chaetognatha Longhair jaw Arrow worms :342 Chitinous spines either side of head, fins 7002100000000000000♠approx. 100 extant
Chordata With a cord Chordates Hollow dorsal nerve cord , notochord , pharyngeal slits , endostyle , post-anal tail 7005100000000000000♠approx. 100,000+
Ctenophora Comb bearer Comb jellies :256 Eight "comb rows" of fused cilia 7002100000000000000♠approx. 100 extant
Cycliophora Wheel carrying _Symbion_ Circular mouth surrounded by small cilia, sac-like bodies 7000300000000000000♠3+
Gastrotricha Hairy stomach :288 Gastrotrich worms Two terminal adhesive tubes 7002690000000000000♠approx. 690
Gnathostomulida Jaw orifice Jaw worms :260
Kinorhyncha Motion snout Mud dragons Eleven segments, each with a dorsal plate 7002150000000000000♠approx. 150
Loricifera Corset bearer Brush heads Umbrella-like scales at each end 7002122000000000000♠approx. 122
Tiny jaw animals
Mollusca Soft :320 Mollusks / molluscs Muscular foot and mantle round shell 7005112000000000000♠112,000
Nematoda Thread like Round worms, thread worms :274 Round cross section, keratin cuticle 7004250000000000000♠25,000–1,000,000
Nematomorpha Thread form :276 Horsehair worms, Gordian worms :276
Nemertea A sea nymph :270 Ribbon worms, Rhynchocoela :270
Onychophora Claw bearer Velvet worms :328 Legs tipped by chitinous claws 7002200000000000000♠approx. 200 extant
Orthonectida Straight swimming :268 Orthonectids :268 Single layer of ciliated cells surrounding a mass of sex cells 7001200000000000000♠approx. 20
Phoronida Zeus's mistress Horseshoe worms U-shaped gut 7001110000000000000♠11
Placozoa Plate animals Trichoplaxes :242 Differentiated top and bottom surfaces, two ciliated cell layers, amoeboid fiber cells in between 7000100000000000000♠1
Platyhelminthes Flat worm :262 Flatworms :262
Porifera * Pore bearer Sponges :246 Perforated interior wall 7003500000000000000♠5,000+ extant
Rhombozoa Lozenge animal Rhombozoans :264 Single anteroposterior axial cell surrounded by ciliated cells 7001750000000000000♠75
Rotifera Wheel bearer Rotifers :282 Anterior crown of cilia 7003200000000000000♠approx. 2,000
Sipuncula Small tube Peanut worms :310 Mouth surrounded by invertible tentacles 7002144000000000000♠144–320
Tardigrada Slow step Water bears, moss piglets :324 Four-segmented body and head 7003100000000000000♠1,000+
Xenacoelomorpha Strange form without gut — Ciliated deuterostome 7000200000000000000♠2
PLANT PHYLA (DIVISIONS)
The kingdom Plantae is defined in various ways by different biologists (see Current definitions of Plantae ). 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 . 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.
The definition and classification of plants at the division level also varies from source to source, and has changed progressively in recent years. Thus some sources place horsetails in division Arthrophyta and ferns in division Pteridophyta, 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), or for conifers alone as below.
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. Where formal ranks have been provided, the traditional divisions listed below have been reduced to a very much lower level, e.g. subclasses .
Land plants Viridiplantae
Other algae ( Biliphyta )
DIVISION MEANING COMMON NAME DISTINGUISHING CHARACTERISTICS SPECIES DESCRIBED
Bryophyta _ Bryum _-like plant, moss plant Mosses Persistent unbranched sporophytes , no vascular system 7004120000000000000♠approx. 12,000
Charophyta _Chara _-like plant Charophytes
Chlorophyta Yellow-green plant :200 Chlorophytes
Glaucophyta Blue-green plant Glaucophytes
Lycophyta _ Lycopodium _-like plant
Wolf plant Clubmosses "> _ Pteris _-like plant, fern plant Ferns ">:396 Ascomycetes, :396 sac fungi
Basidiomycota Small base fungus :402 Basidiomycetes :402
Blastocladiomycota Offshoot branch fungus Blastoclads
Glomeromycota Ball of yarn fungus :394 Glomeromycetes, AM fungi :394
Neocallimastigomycota New beautiful whip fungus Neocallimastigomycetes
Zygomycota Pair fungus :392 Zygomycetes :392
PROTISTA PHYLA (DIVISIONS)
Main article: Protista taxonomy
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. :120 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. Proposals have been made to divide it among several new kingdoms, such as Protozoa and Chromista in the Cavalier-Smith system .
Protist taxonomy has long been unstable, with different approaches
and definitions resulting in many competing classification schemes.
The phyla listed here are used for
Protozoa by the
PHYLUM/DIVISION MEANING COMMON NAME DISTINGUISHING CHARACTERISTICS EXAMPLE
Amoebozoa Amorphous animal Amoebas
Bigyra Two ring
Choanozoa Funnel animal
Euglenozoa True eye animal
Foraminifera Hole bearers Forams Complex shells with one or more chambers Forams
Loukozoa Groove animal
Myzozoa Suckling animal
Ochrophyta Yellow plant Diatoms
Radiozoa Ray animal Radiolarians
Main article: Bacterial phyla
Currently there are 29 phyla accepted by List of Prokaryotic names with Standing in Nomenclature (LPSN)
Acidobacteria , phenotipically diverse and mostly uncultured
Actinobacteria , High-G+C Gram positive species
Aquificae , only 14 thermophilic genera, deep branching
Caldiserica , formerly candidate division OP5, _Caldisericum
exile_ is the sole representative
Chlamydiae , only 6 genera
Currently there are 5 phyla accepted by List of Prokaryotic names with Standing in Nomenclature (LPSN).
* Biology portal
* ^ _A_ _B_ McNeill, J.; et al., eds. (2012). _International Code
of Nomenclature for algae, fungi, and plants (Melbourne Code), Adopted
by the Eighteenth International Botanical Congress Melbourne,
Australia, July 2011_ (electronic ed.). International Association for
_ Look up PHYLUM _ in Wiktionary, the free dictionary.
* Are phyla "real"? Is there really a well-defined "number of