Phylum

For other uses, see Phyla.

The hierarchy of biological classification's eight major taxonomic ranks, which is an example of definition by genus and differentia. A kingdom contains one or more phyla. Intermediate minor rankings are not shown.

In biology, a phylum (English pronunciation: /ˈfaɪləm/; plural: phyla) is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division. 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, 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). 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. 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. 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.

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 off-shoots that diverged from a phylum's history 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. 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. aspects of the "body plan" of the phylum without all the characters necessary to fall within it. This weakens the idea that each of the phyla represents a distinct body plan.

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.

Lists

Animal phyla

Phylum	Meaning	Common name	Distinguishing characteristic	Species described
!a	!a	!a	!a	-9e99
Acanthocephala	Thorny headed worms	Thorny-headed worms	Reversible spiny proboscis	756 approx.
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	100 extant approx.
Chordata	Cord	Chordates	Hollow dorsal nerve cord, notochord, pharyngeal slits, endostyle, post-anal tail	100,000+ approx.
Cnidaria	Stinging nettle	Coelenterates	Nematocysts (stinging cells)	11,000 approx.
Ctenophora	Comb bearer	Comb jellies	Eight "comb rows" of fused cilia	100 extant approx.
Cycliophora	Wheel carrying	Symbion	Circular mouth surrounded by small cilia	3+
Echinodermata	Spiny skin	Echinoderms	Fivefold radial symmetry in living forms, mesodermal calcified spines	7,000 extant approx.; 13,000 extinct approx.
Entoprocta	Inside anus	Goblet worm	Anus inside ring of cilia	150 approx.
Gastrotricha	Hair stomach	Meiofauna	Two terminal adhesive tubes	690 approx.
Gnathostomulida	Jaw orifice	Jaw worms		100 approx.
Hemichordata	Half cord	Acorn worms, pterobranchs	Stomochord in collar, pharyngeal slits	100 extant approx.
Kinorhyncha	Motion snout	Mud dragons	Eleven segments, each with a dorsal plate	150 approx.
Loricifera	Corset bearer	Brush heads	Umbrella-like scales at each end	122 approx.
Micrognathozoa	Tiny jaw animals	—	Accordion like extensible thorax	1
Mollusca	Soft	Mollusks / molluscs	Muscular foot and mantle round shell	112,000
Nematoda	Thread like	Round worms	Round cross section, keratin cuticle	80,000–1,000,000
Nematomorpha	Thread form	Horsehair worms		320 approx.
Nemertea	A sea nymph	Ribbon worms		1,200 approx.
Onychophora	Claw bearer	Velvet worms	Legs tipped by chitinous claws	200 extant approx.
Orthonectida	Straight swim		Single layer of ciliated cells surrounding a mass of sex cells	20 approx.
Phoronida	Zeus's mistress	Horseshoe worms	U-shaped gut	20
Placozoa	Plate animals			1
Platyhelminthes	Flat worms	Flat worms		25,000 approx.
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	2,000 approx.
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
~z	~z	~z	~z	9e99
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
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

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

• Cladistics
• Phylogenetics
• Systematics
• Taxonomy

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