Phylum

Phylum is a rank in the taxonomic hierarchy, directly below Kingdom and above Class. It is used in the classification of organisms to group together those with similar characteristics. The term "phylum" is derived from the Greek word phulon, which means "race" or "stock".

Definition

In biological taxonomy, a phylum (plural: phyla) is a 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.

History

The concept of phylum has its roots in the system of Carolus Linnaeus, who grouped species according to characteristics that were easy to observe. The idea of a phylum was further developed by Ernst Haeckel, a German biologist and philosopher who created a system of animal classification that included 20 phyla.

Use in classification

The use of the term "phylum" has been criticised for its lack of precision. Some scientists prefer to use the term "division", particularly in the classification of bacteria, algae and fungi, while others use the term "group". Despite these criticisms, "phylum" remains widely used in scientific literature and in educational materials.

Examples of phyla

There are several examples of phyla in both the animal and plant kingdoms. In the animal kingdom, for example, the phylum Chordata includes all animals with a dorsal nerve cord, such as mammals, birds, reptiles, amphibians, and fish. In the plant kingdom, the phylum Bryophyta includes all mosses.

Known phyla

Animals

Main article: Animal

Total numbers are estimates; figures from different authors vary widely, not least because some are based on described species, while others 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.

Phylum	Meaning	Common Name	Distinguishing Characteristic	Taxa Described
Agmata	Fragmented		Calcareous conical shells	5 species, extinct
Annelida	Little ring	Segmented worms, annelids	Multiple circular segments	22,000+ extant
Arthropoda	Jointed foot	Arthropods	Segmented bodies and jointed limbs, with Chitin exoskeleton	1,250,000+ extant; 20,000+ extinct
Brachiopoda	Arm foot	Lampshells	Lophophore and pedicle	300–500 extant; 12,000+ extinct
Bryozoa	Moss animals	Moss animals, sea mats, ectoprocts	Lophophore, no pedicle, ciliated tentacles, anus outside ring of cilia	6,000 extant
Chaetognatha	Longhair jaw	Arrow worms	Chitinous spines either side of head, fins	approx. 100 extant
Chordata	With a cord	Chordates	Hollow dorsal nerve cord, notochord, pharyngeal slits, endostyle, post-anal tail	approx. 55,000+
Cnidaria	Stinging nettle	Cnidarians	Nematocysts (stinging cells)	approx. 16,000
Ctenophora	Comb bearer	Comb jellies	Eight "comb rows" of fused cilia	approx. 100–150 extant
Cycliophora	Wheel carrying		Circular mouth surrounded by small cilia, sac-like bodies	3+
Dicyemida	Lozenge animal		Single anteroposterior axial celled endoparasites, surrounded by ciliated cells	100+
Echinodermata	Spiny skin	Echinoderms	Fivefold radial symmetry in living forms, mesodermal calcified spines	approx. 7,500 extant; approx. 13,000 extinct
Entoprocta	Inside anus	Goblet worms	Anus inside ring of cilia	approx. 150
Gastrotricha	Hairy stomach	Hairybellies	Two terminal adhesive tubes	approx. 690
Gnathostomulida	Jaw orifice	Jaw worms	Tiny worms related to rotifers with no body cavity	approx. 100
Hemichordata	Half cord	Acorn worms, hemichordates	Stomochord in collar, pharyngeal slits	approx. 130 extant
Kinorhyncha	Motion snout	Mud dragons	Eleven segments, each with a dorsal plate	approx. 150
Loricifera	Armour bearer	Brush heads	Umbrella-like scales at each end	approx. 122
Micrognathozoa	Tiny jaw animals		Accordion-like extensible thorax	1
Mollusca	Soft	Mollusks	Muscular foot and mantle round shell	85,000+ extant; 80,000+ extinct
Monoblastozoa	One sprout animals		distinct anterior/posterior parts and being densely ciliated, especially around the "mouth" and "anus".	1
Nematoda	Thread like	Roundworms, threadworms, eelworms, nematodes	Round cross section, keratin cuticle	25,000
Nematomorpha	Thread form	Horsehair worms, Gordian worms	Long, thin parasitic worms closely related to nematodes	approx. 320
Nemertea	A sea nymph	Ribbon worms	Unsegmented worms, with a proboscis housed in a cavity derived from the coelom called the rhynchocoel	approx. 1,200
Onychophora	Claw bearer	Velvet worms	Worm-like animal with legs tipped by chitinous claws	approx. 200 extant
Orthonectida	Straight swimmer		Parasitic, microscopic, simple, wormlike organisms	20
Petalonamae	Shaped like leaves		An extinct phylum from the Ediacaran. They are bottom-dwelling and immobile, shaped like leaves (frondomorphs), feathers or spindles.	3 classes, extinct
Phoronida	Zeus's mistress	Horseshoe worms	U-shaped gut	11
Placozoa	Plate animals	Trichoplaxes, placozoans	Differentiated top and bottom surfaces, two ciliated cell layers, amoeboid fiber cells in between	4+
Platyhelminthes	Flat worm	Flatworms	Flattened worms with no body cavity. Many are parasitic.	approx. 29,500
Porifera	Pore bearer	Sponges	Perforated interior wall, simplest of all known animals	10,800 extant
Priapulida	Little Priapus	Penis worms	Penis-shaped worms	approx. 20
Proarticulata	Before articulates		An extinct group of mattress-like organisms that display "glide symmetry." Found during the Ediacaran.	3 classes, extinct
Rotifera	Wheel bearer	Rotifers	Anterior crown of cilia	approx. 3,500
Saccorhytida	Saccus : "pocket" and "wrinkle"		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 ecdysozoan.	2 species, extinct
Tardigrada	Slow step	Water bears, moss piglets	Microscopic relatives of the arthropods, with a four segmented body and head	1,000
Trilobozoa	Three-lobed animal	Trilobozoans	A taxon of mostly discoidal organisms exhibiting tricentric symmetry. All are Ediacaran-aged	18 genera, extinct
Vetulicolia	Ancient dweller	Vetulicolians	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	Xenacoelomorphs	Small, simple animals. Bilaterian, but lacking typical bilaterian structures such as gut cavities, anuses, and circulatory systems	400+

Total: 39 phyla, approx. 1,525,000 species described

Plants

Main article: Plant

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.

Phylum	Meaning	Common Name	Distinguishing Characteristic	Taxa Described
Anthocerotophyta	Hornworts	Hornworts	Simple plants that have a horn-like structure used for spore dispersal	200+ species
Bryophyta	Mosses	Mosses	Simple plants without vascular tissue, requiring water for reproduction	approx. 12,000 species
Charophyta	Green algae	Charophytes	Green algae that are closely related to land plants	approx. 200 species
Chlorophyta	Green algae	Chlorophytes	Green algae with a wide range of morphologies	approx. 7,000 species
Glaucophyta	Glaucophytes	Glaucophytes	Unicellular algae with blue-green plastids	approx. 13 species
Marchantiophyta	Liverworts	Liverworts	Simple, non-vascular plants with a flat thallus or leafy structures	6,000+ species
Mosses			Simple plants without vascular tissue	Approx. 12,000 species
Pteridophyta	Ferns	Ferns	Vascular plants that reproduce via spores, with large fronds	approx. 10,000 species
Pinophyta	Conifers	Conifers	Vascular plants that reproduce via cones	approx. 600 species
Cycadophyta	Cycads	Cycads	Seed plants with large, leathery leaves and cones	approx. 300 species
Ginkgophyta	Ginkgos	Ginkgos	Seed plants with fan-shaped leaves	1 species
Angiosperms		Flowering plants	Seed plants that produce flowers and fruits	approx. 250,000 species

Total: approx. 270,000 species described

Fungi

Main article: Fungi

Fungi represent a large and diverse kingdom of eukaryotic organisms that includes yeasts, molds, and mushrooms. They play critical roles in decomposition, nutrient cycling, and symbiotic relationships with plants. Fungal taxonomy is based primarily on reproductive structures, as the organisms often exhibit a high degree of morphological variation.

Phylum	Meaning	Common Name	Distinguishing Characteristic	Taxa Described
Ascomycota	Sac fungi	Ascomycetes	Produces spores (ascospores) inside a sac-like structure (ascus)	64,000+ species
Basidiomycota	Club fungi	Basidiomycetes	Produces spores (basidiospores) on a club-shaped structure (basidium)	30,000+ species
Zygomycota	Zygote fungi	Zygomycetes	Produces sexual spores (zygospore) after the fusion of two haploid cells	1,000+ species
Chytridiomycota	Chytrid fungi	Chytrids	Aquatic fungi, often parasitic, with flagellated spores (zoospores)	approx. 1,000 species
Glomeromycota	Arbuscular mycorrhizal fungi	Arbuscular mycorrhizae	Forms symbiotic relationships with plant roots to aid in nutrient absorption	approx. 250 species

Total: approx. 100,000 species described

Protists

Main article: Protist

Protists are a diverse group of eukaryotic microorganisms that do not fit neatly into the categories of animals, plants, or fungi. This group includes unicellular organisms such as protozoa and algae, as well as some multicellular organisms. The kingdom Protista is no longer considered valid in modern classifications, and many protists are now placed into separate supergroups based on genetic relationships.

Phylum	Meaning	Common Name	Distinguishing Characteristic	Taxa Described
Amoebozoa	Blob animals	Amoeboids	Amoeboid movement using pseudopodia; includes slime molds and amoebas	approx. 1,500 species
Archaeplastida	Ancient plastid	Red algae, green algae, land plants	Photosynthetic organisms with plastids derived from endosymbiosis	approx. 15,000 species
Chromalveolata	Color enveloped	Alveolates, Stramenopiles	Includes diverse groups such as ciliates, dinoflagellates, and brown algae	approx. 35,000 species
Excavata	Excavation	Euglenozoa, Diplomonads	Includes flagellates and parasites like trypanosomes	approx. 1,000 species
Rhizaria	Root	Foraminifera, Radiolaria	Single-celled, mostly marine organisms with complex, mineralized shells	approx. 7,000 species
Opistokonta	Posterior pole	Fungi, Animals, Choanoflagellates	Includes animals, fungi, and some related protists with a single posterior flagellum in their cells	approx. 100,000 species

Total: approx. 100,000 species described

Bacteria

Main article: Bacterium

Bacteria are single-celled organisms that belong to the domain Bacteria and are among the most diverse and abundant organisms on Earth. They have a simple cellular structure, lack a nucleus, and reproduce via binary fission. Bacteria play vital roles in ecosystems, including nitrogen fixation, decomposition, and symbiosis.

Phylum	Meaning	Common Name	Distinguishing Characteristic	Taxa Described
Actinobacteria	Actinobacteria	Actinobacteria	High G+C content, gram-positive bacteria, often found in soil	approx. 20,000 species
Firmicutes	Strong skin	Firmicutes	Gram-positive bacteria with a thick cell wall, including many pathogens	approx. 4,000 species
Proteobacteria	Proteus	Proteobacteria	Diverse group with a wide range of metabolic activities, including many pathogens	approx. 10,000 species
Bacteroidetes	Stick shaped	Bacteroidetes	Gram-negative bacteria often found in the gut of animals	approx. 6,000 species
Cyanobacteria	Blue-green	Cyanobacteria	Photosynthetic bacteria, often forming colonies, and important in oxygen production	approx. 2,000 species
Spirochaetes	Coil shape	Spirochetes	Corkscrew-shaped bacteria, many of which are pathogenic	approx. 700 species

Total: approx. 20,000 species described

Archaea

Main article: Archaea

Archaea are single-celled organisms that are similar in size and shape to bacteria but differ genetically and biochemically. They often live in extreme environments, such as hot springs, salt lakes, and deep-sea hydrothermal vents, although many also exist in more typical environments. Archaea are considered one of the three domains of life, along with bacteria and eukaryotes.

Phylum	Meaning	Common Name	Distinguishing Characteristic	Taxa Described
Euryarchaeota	Broad archaea	Methanogens, Halophiles	Includes organisms that produce methane or live in extreme environments like salt lakes	approx. 250 species
Crenarchaeota	Cold archaea	Thermophiles	Includes organisms that thrive in extreme heat, such as hot springs and deep-sea vents	approx. 200 species
Thaumarchaeota	Wonder archaea	Ammonia oxidizers	Archaea involved in nitrogen cycling, particularly ammonia oxidation	approx. 100 species

Total: approx. 600 species described

Protist Gallery

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  Amoeba proteus

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  Toxoplasma gondii

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  Podomonas kaiyoae

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  Aplanonet

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  Euglypha species

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  Vitrella brassicaformis

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  Desmarella moniliformis

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  Paramecium bursaria

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  Rhodomonas salina

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  Dinoflagellate species

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  Vampyrella lateritia

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  Stygiella incarcerata

See also

• Taxonomy
• Kingdom
• Class
• Order
• Family
• Genus
• Species

Phylum Resources
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