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In biology, a phylum (; 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 contains about 31 phyla, the plant kingdom Plantae contains about 14 phyla, 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 Ecdysozoa and Embryophyta.
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.
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.
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 "" 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.
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 Monilophyta, while others place them both in Monilophyta, as shown below. The division Pinophyta may be used for all (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.
Phylum Microsporidia is generally included in kingdom Fungi, though its exact relations remain uncertain, and it is considered a 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.
Protist taxonomy has long been unstable, with different approaches and definitions resulting in many competing classification schemes. The phyla listed here are used for Chromista and Protozoa by the Catalogue of Life, adapted from the system used by the International Society of Protistologists.
The Catalogue of Life includes Rhodophyta and Glaucophyta in kingdom Plantae, but other systems consider these phyla part of Protista.
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.
Known phyla
Animals
Total numbers are estimates; figures from different authors vary wildly, not least because some are based on described species, some on extrapolations to numbers of undescribed species. For instance, around 25,000–27,000 species of nematodes have been described, while published estimates of the total number of nematode species include 10,000–20,000; 500,000; 10 million; and 100 million.
[[Protostome]] [[Bilateria]] [[Nephrozoa]]
[[Deuterostome]]
Basal/disputed Non-Bilateria
[[Vendobionta]]
[[Parazoa]]
Others
Annelida Little ring Segmented worms Multiple circular segments + extant Agmata Fragmented Agmates Calcareous conical shells 5 species, extinct Archaeocyatha Ancient cups Archaeocyathids An extinct taxon of sponge-grade, reef-building organisms living in warm tropical and subtropical waters during the Early Cambrian. 3 known classes (Extinct) Arthropoda Jointed foot Arthropods Segmented bodies and jointed limbs, with Chitin exoskeleton + extant; 20,000+ extinct Brachiopoda Arm foot Lampshells Lophophore and pedicle Bryozoa (Ectoprocta) Moss animals Moss animals, sea mats, ectoprocts Lophophore, no pedicle, , anus outside ring of cilia extant Chaetognatha Longhair jaw Arrow worms spines either side of head, fins extant Chordata With a cord Chordates Hollow dorsal nerve cord, notochord, , endostyle, post-anus tail + Cnidaria Stinging nettle Cnidarians Nematocysts (stinging cells) Ctenophora Comb bearer Comb jellies Eight "comb rows" of fused cilia Cycliophora Wheel carrying Symbion Circular mouth surrounded by small cilia, sac-like bodies + Echinodermata Spiny skin Echinoderms Fivefold radial symmetry in living forms, mesodermal calcified spines extant; approx. 13,000 extinct Entoprocta Inside anus Goblet worms Anus inside ring of cilia Gastrotricha Hairy stomach Gastrotrich worms Two terminal adhesive tubes Gnathostomulida Jaw orifice Jaw worms Tiny worms related to rotifers with no body cavity Hemichordata Half cord Acorn worms, hemichordates Stomochord in collar, extant Kinorhyncha Motion snout Mud dragons Eleven segments, each with a dorsal plate Loricifera Corset bearer Brush heads Umbrella-like scales at each end Limnognathia Tiny jaw animals Limnognathia Accordion-like extensible thorax Medusoid Jellyfish-like Medusoids These are extinct creatures described as jellyfish-like and inhabited the late Precambrian, Ediacaran and early Cambrian. 18 genera, extinct Mollusca Soft Mollusks / molluscs Muscular foot and mantle round shell + extant; 80,000+ extinctFeldkamp, S. (2002) Modern Biology. Holt, Rinehart, and Winston, USA. (pp. 725) Nematoda Thread like Round worms, thread worms Round cross section, keratin cuticle Nematomorpha Thread form Horsehair worms, gordian worms Long, thin parasitic worms closely related to nematodes Nemertea A sea nymph Ribbon worms, rhynchocoela Unsegmented worms, with a proboscis housed in a cavity derived from the coelom called the rhynchocoel Onychophora Claw bearer Velvet worms Worm-like animal with legs tipped by chitinous claws extant Petalonamae Shaped like leaves No An extinct phylum from the Ediacaran. They are bottom-dwelling and immobile, shaped like leaves (frondomorphs), feathers or spindles. 3 classes, extinct Zeus's mistress Horseshoe worms U-shaped gut Placozoa Plate animals Trichoplaxes Differentiated top and bottom surfaces, two ciliated cell layers, amoeboid fiber cells in between Platyhelminthes Flat worm Flatworms Flattened worms with no body cavity. Many are parasitic. Porifera Pore bearer Sponges Perforated interior wall, simplest of all known animals extant Priapulida Little Priapus Penis worms Penis-shaped worms Proarticulata Before articulates Proarticulates An extinct group of mattress-like organisms that display "glide symmetry." Found during the Ediacaran. 3 classes, extinct Rhombozoa (Dicyemida) Lozenge animal Rhombozoans Single anteroposterior axial celled endoparasites, surrounded by ciliated cells + Rotifera Wheel bearer Rotifers Anterior crown of cilia Saccorhytida Saccus : "pocket" and "wrinkle" Saccorhytus Saccorhytus is only about 1 mm (1.3 mm) in size and is characterized by a spherical or hemispherical body with a prominent mouth. Its body is covered by a thick but flexible cuticle. It has a nodule above its mouth. Around its body are 8 openings in a truncated cone with radial folds. Considered to be a deuterostome or an early Ecdysozoa. 1 species, extinct Tardigrada Slow step Water bears, Moss piglets Microscopic relatives of the arthropods, with a four segmented body and head Trilobozoa Three-lobed animal Trilobozoan A taxon of mostly discoidal organisms exhibiting tricentric symmetry. All are Ediacaran-aged 18 genera, extinct Vetulicolia Ancient dweller Vetulicolian Might possibly be a subphylum of the chordates. Their body consists of two parts: a large front part and covered with a large "mouth" and a hundred round objects on each side that have been interpreted as gills or openings near the pharynx. Their posterior pharynx consists of 7 segments. 15 species, extinct Xenacoelomorpha Strange hollow form Subphylum Acoelomorpha and xenoturbellida Small, simple animals. , but lacking typical bilaterian structures such as gut cavities, anuses, and circulatory systems + Total: 40 1,525,000
Plants
The kingdom Plantae is defined in various ways by different biologists (see Current definitions of Plantae). All definitions include the living (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.
Embryophyte]] [[Viridiplantae]]
[[Green algae]]
Other algae ([[Biliphyta]])
Anthocerotophyta p. 489 Anthoceros-like plants Hornworts Horn-shaped , no vascular system -300+ Moss Bryum-like plants, moss plants Mosses Persistent unbranched , no vascular system Charophyta Chara-like plants Charophytes Chlorophyta (Yellow-)green plants Chlorophytes Cycadophyta Cycas-like plants, palm-like plants Cycads Seeds, crown of compound leaves -200 Ginkgophyta Ginkgo-like plants Ginkgo, maidenhair tree Seeds not protected by fruit (single living species) extant; 50+ extinct Glaucophyta Blue-green plants Glaucophytes Gnetophyta Gnetum-like plants Gnetophytes Seeds and woody vascular system with vessels Lycopodiophyta,
LycophytaLycopodium-like plants
Wolf plantsClubmosses & spikemosses Microphyll leaf, vascular system extant Flowering plant Magnolia-like plants Flowering plants, angiosperms Flowers and fruit, vascular system with vessels Marchantiophyta, (2022). 9780521660976, Cambridge University Press. ISBN 9780521660976
HepatophytaMarchantia-like plants
Liver plantsLiverworts Ephemeral unbranched , no vascular system Fern,
Monilophyta Polypodium-like plants Ferns Megaphyll leaf, vascular system Pinophyta,
ConiferophytaPinus-like plants
Cone-bearing plantConifers Cones containing seeds and wood composed of tracheids extant Rhodophyta Rose plants Red algae Use as accessory pigments. Total: 14
Fungi
Ascomycota Bladder fungus Ascomycetes, sac fungi Tend to have fruiting bodies (ascocarp). Filamentous, producing hyphae separated by septa. Can reproduce asexually. 30,000 Basidiomycota Small base fungus Basidiomycetes, club fungi Bracket fungi, toadstools, smuts and rust. Sexual reproduction. 31,515 Blastocladiomycota Offshoot branch fungus Blastoclads Less than 200 Chytridiomycota Little cooking pot fungus Chytrids Predominantly Aquatic saprotrophic or parasitic. Have a posterior flagellum. Tend to be single celled but can also be multicellular. 1000+ Glomeromycota Ball of yarn fungus Glomeromycetes, fungi Mainly arbuscular mycorrhizae present, terrestrial with a small presence on wetlands. Reproduction is asexual but requires plant roots. 284 Microsporidia Small seeds Microsporans 1400 Neocallimastigomycota New beautiful whip fungus Neocallimastigomycetes Predominantly located in digestive tract of herbivorous animals. Anaerobic, terrestrial and aquatic. approx. 20 Zygomycota Pair fungus Zygomycetes Most are saprobes and reproduce sexually and asexually. aprox. 1060 Total: 8
Protista
Kingdom Protista (or Protoctista) is included in the traditional five- or six-kingdom model, where it can be defined as containing all that are not plants, animals, or fungi. Protista is a polyphyletic taxon, 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.
[[Harosa]]
[[Protozoa]]
Amoebozoa Amorphous animal Amoebas Presence of pseudopodia Amoeba 2400 Bigyra Two rings Cercozoa Choanozoa Funnel animal Presence of a colar of microvilli surrounding a flagellum 125 Ciliophora Cilia bearer Ciliates Presence of multiple cilia and a cytostome Paramecium 4500 Cryptista Hidden Euglenozoa True eye animal Euglena 800 Foraminifera Hole bearers Forams Complex shells with one or more chambers Forams 10000, 50000 extinct Haptophyta Loukozoa Groove animal Metamonada Middle single-celled organisms Giardia Microsporidia Small spore Myzozoa Suckling animal 1555+ Ochrophyta Yellow plant Diatoms Oomycota Egg fungus Oomycetes Percolozoa Radiozoa Ray animal Radiolarians Sarcomastigophora Flesh and whip bearer Sulcozoa Total: 19
Bacteria
Currently there are 40 bacterial phyla (not including "Cyanobacteria") that have been validly published according to the Bacteriological Code
Archaea
Currently there are 2 phyla that have been validly published according to the Bacteriological Code
Other phyla that have been proposed, but not validly named, include:
See also
External links
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