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 33 phyla, the plant kingdom
Plantae contains about 14,
and the fungus kingdom
Fungi contains about 8 phyla. Current research
in phylogenetics is uncovering the relationships between phyla, which
are contained in larger clades, like
1 General description and familiar examples
1.1 Definition based on genetic relation
1.2 Definition based on body plan
2 Known phyla
2.1 Animal phyla
Plant phyla (divisions)
2.3 Fungal divisions
Protista phyla (divisions)
2.5 Bacterial phyla/divisions
2.6 Archaeal phyla/division/kingdoms
3 See also
6 External links
General description and familiar examples
The term phylum was coined in 1866 by
Ernst Haeckel from the Greek
phylon (φῦλον, "race, stock"), related to phyle (φυλή,
"tribe, clan"). In plant taxonomy,
August W. Eichler
August W. 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 embranchements of Georges Cuvier.
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.[citation
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
Mesozoa was divided into two phyla (
Orthonectida and Rhombozoa)
when it was discovered the
Orthonectida are probably deuterostomes and
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
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.[clarification needed] 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.[clarification needed] 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[clarification needed].
Representatives of many modern phyla did not appear until long after
the Cambrian.[clarification needed]
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Others (Radiata or Parazoa)
Reversible spiny proboscis that bears many rows of hooked spines
Multiple circular segment
Segmented bodies and jointed limbs, with
7006120000000000000♠1,200,000+ extant; 20,000+ extinct
Lophophore and pedicle
7002300000000000000♠300-500 extant; 12,000+ extinct
Moss animals, sea mats, ectoprocts:332
Lophophore, no pedicle, ciliated tentacles, anus outside ring of cilia
Chitinous spines either side of head, fins
7002100000000000000♠approx. 100 extant
With a cord
Hollow dorsal nerve cord, notochord, pharyngeal slits, endostyle,
Nematocysts (stinging cells)
Eight "comb rows" of fused cilia
7002100000000000000♠approx. 100-150 extant
Circular mouth surrounded by small cilia, sac-like bodies
Fivefold radial symmetry in living forms, mesodermal calcified spines
7003700000000000000♠approx. 7,000 extant; approx. 13,000
Anus inside ring of cilia
Two terminal adhesive tubes
Acorn worms, hemichordates
Stomochord in collar, pharyngeal slits
7002130000000000000♠approx. 130 extant
Eleven segments, each with a dorsal plate
Umbrella-like scales at each end
Tiny jaw animals
Accordion-like extensible thorax
Mollusks / molluscs
Muscular foot and mantle round shell
7004900000000000000♠90,000+ extant; 80,000+ extinct
Round worms, thread worms:274
Round cross section, keratin cuticle
Horsehair worms, Gordian worms:276
A sea nymph:270
Ribbon worms, Rhynchocoela:270
Legs tipped by chitinous claws
7002200000000000000♠approx. 200 extant
Single layer of ciliated cells surrounding a mass of sex cells
Differentiated top and bottom surfaces, two ciliated cell layers,
amoeboid fiber cells in between
Perforated interior wall
Single anteroposterior axial cell surrounded by ciliated cells
Anterior crown of cilia
Mouth surrounded by invertible tentacles
Water bears, moss piglets:324
Four-segmented body and head
Strange form without gut
Plant phyla (divisions)
Main article: Plant
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
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
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,
Other algae (Biliphyta)
Horn-shaped sporophytes, no vascular system
Bryum-like plant, moss plant
Persistent unbranched sporophytes, no vascular system
Cycas-like plant, palm-like plant
Seeds, crown of compound leaves
Ginkgo, maidenhair tree
Seeds not protected by fruit (single living species)
7000100000000000000♠only 1 extant; 50+ extinct
Seeds and woody vascular system with vessels
Clubmosses & spikemosses
Microphyll leaves, vascular system
Flowering plants, angiosperms
Flowers and fruit, vascular system with vessels
Ephemeral unbranched sporophytes, no vascular system
Cones containing seeds and wood composed of tracheids
Pteris-like plant, fern plant
Ferns & horsetails
Prothallus gametophytes, vascular system
7003900000000000000♠approx. 9,000 (not including lycophytes)
Main article: Fungi
Ascomycetes,:396 sac fungi
Small base fungus:402
Offshoot branch fungus
Little cooking pot fungus
Ball of yarn fungus:394
Glomeromycetes, AM fungi:394
New beautiful whip fungus
Microsporidia is generally included in kingdom Fungi, though
its exact relations remain uncertain, and it is considered a
protozoan by the International Society of Protistologists (see
Protista, below). Molecular analysis of
Zygomycota has found it to be
polyphyletic (its members do not share an immediate ancestor),
which is considered undesirable by many biologists. Accordingly, there
is a proposal to abolish the
Zygomycota phylum. Its members would be
divided between phylum
Glomeromycota and four new subphyla incertae
sedis (of uncertain placement): Entomophthoromycotina,
Kickxellomycotina, Mucoromycotina, and Zoopagomycotina.
Protista phyla (divisions)
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
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
Chromista in the Cavalier-Smith
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
Catalogue of Life, adapted from the system used by the
International Society of Protistologists.
True eye animal
Complex shells with one or more chambers
The Catalogue of
Glaucophyta in kingdom
Plantae, but other systems consider these phyla part of
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
Chlorobi, only 7 genera, green sulphur bacteria
Chloroflexi, green non-sulphur bacteria
Chrysiogenetes, only 3 genera (Chrysiogenes arsenatis, Desulfurispira
natronophila, Desulfurispirillum alkaliphilum)
Cyanobacteria, also known as the blue-green algae
Deinococcus-Thermus, Deinococcus radiodurans and Thermus aquaticus are
"commonly known" species of this phyla
Elusimicrobia, formerly candidate division Thermite Group 1
Firmicutes, Low-G+C Gram positive species, such as the spore-formers
Bacilli (aerobic) and
Lentisphaerae, formerly clade VadinBE97
Proteobacteria, the most known phyla, containing species such as
Escherichia coli or Pseudomonas aeruginosa
Spirochaetes, species include Borrelia burgdorferi, which causes Lyme
Tenericutes, alternatively class
Mollicutes in phylum Firmicutes
(notable genus: Mycoplasma)
Thermotogae, deep branching
Currently there are 5 phyla accepted by List of Prokaryotic names with
Standing in Nomenclature (LPSN).
Crenarchaeota, second most common archaeal phylum
Euryarchaeota, most common archaeal phylum
Nanoarchaeota, ultra-small symbiotes, single known species
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Phylum in Wiktionary, the free dictionary.
Are phyla "real"? Is there really a well-defined "number of animal
phyla" extant and in the fossil record?
Major Phyla Of Animals