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A flagellate is a cell or organism with one or more
whip A whip is a tool or weapon designed to strike humans or other animals to exert control through pain compliance or fear of pain. They can also be used without inflicting pain, for audiovisual cues, such as in equestrianism. They are generally e ...
-like
appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body. In arthropods, an appendage refers to any of the homologous body parts that may extend from a body segment, including anten ...
s called
flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...
. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and
eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
s and their means of motion. The term presently does not imply any specific relationship or classification of the organisms that possess flagella. However, the term "flagellate" is included in other terms (such as "
dinoflagellate The dinoflagellates (Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...
" and " choanoflagellata") which are more formally characterized.


Form and behavior

Flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...
in eukaryotes are supported by
microtubule Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27  nm and have an inner diameter between 11 an ...
s in a characteristic arrangement, with nine fused pairs surrounding two central singlets. These arise from a basal body. In some flagellates, flagella direct food into a
cytostome A cytostome (from ''cyto-'', cell and ''stome-'', mouth) or cell mouth is a part of a cell specialized for phagocytosis, usually in the form of a microtubule-supported funnel or groove. Food is directed into the cytostome, and sealed into vacuole ...
or mouth, where food is
ingested Ingestion is the consumption of a substance by an organism. In animals, it normally is accomplished by taking in a substance through the mouth into the gastrointestinal tract, such as through eating or drinking. In single-celled organisms inges ...
. Flagella often support hairs, called mastigonemes, or contain rods. Their ultrastructure plays an important role in classifying
eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
s. Among
protoctist A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the excl ...
s and microscopic animals, a flagellate is an organism with one or more flagella. Some cells in other animals may be flagellate, for instance the spermatozoa of most animal phyla. Flowering plants do not produce flagellate cells, but ferns, mosses, green algae, and some gymnosperms and closely related plants do so. Likewise, most fungi do not produce cells with flagellae, but the primitive fungal chytrids do. Many protists take the form of single-celled flagellates. Flagella are generally used for propulsion. They may also be used to create a current that brings in food. In most such organisms, one or more flagella are located at or near the anterior of the cell, e.g., '' Euglena''. Often there is one directed forwards and one trailing behind. Among animals, fungi, which are part of a group called the opisthokonts, there is a single posterior flagellum. They are from the phylum Mastigophora. They can cause diseases and are typically heterotrophic. They reproduce by binary fission. They spend most of their existence moving or feeding. Many parasites that affect human health or economy are flagellates. Flagellates are the major consumers of primary and secondary production in aquatic ecosystems - consuming bacteria and other protists.


Flagellates as specialized cells or life cycle stages

An overview of the occurrence of flagellated cells in eukaryote groups, as specialized cells of multicellular organisms or as life cycle stages, is given below (see also the article flagellum):Adl et al. (2012). * Archaeplastida: most
green algae The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...
( zoospores and male gametes, except in Zygnematophyceae), bryophytes (male gametes),
pteridophyte A pteridophyte is a vascular plant (with xylem and phloem) that disperses spores. Because pteridophytes produce neither flowers nor seeds, they are sometimes referred to as "cryptogams", meaning that their means of reproduction is hidden. Ferns, ...
s (male gametes), some gymnosperms ( cycads and '' Ginkgo'', as male gametes) * Stramenopiles: centric
diatom A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...
s (male gametes), brown algae (zoospores and gametes), oomycetes (assexual zoospores and gametes), hyphochytrids (zoospores),
labyrinthulomycetes The Labyrinthulomycetes (ICBN) or Labyrinthulea (ICZN) are a class of protists that produce a network of filaments or tubes, which serve as tracks for the cells to glide along and absorb nutrients for them. The two main groups are the labyrint ...
(zoospores), some chrysophytes, some
xanthophyte Yellow-green algae or the Xanthophyceae (xanthophytes) are an important group of heterokont algae. Most live in fresh water, but some are found in marine and soil habitats. They vary from single-celled flagellates to simple colonial and filament ...
s,
eustigmatophyte Eustigmatophytes are a small group (17 genera; ~107 species) of eukaryotic forms of algae that includes marine, freshwater and soil-living species. All eustigmatophytes are unicellular, with coccoid cells and polysaccharide cell walls. Eusti ...
s * Alveolata: some
apicomplexan The Apicomplexa (also called Apicomplexia) are a large phylum of parasitic alveolates. Most of them possess a unique form of organelle that comprises a type of non-photosynthetic plastid called an apicoplast, and an apical complex structure. The ...
s (gametes) * Rhizaria: some radiolarians (probably gametes), foraminiferans (as gametes) **
Cercozoa Cercozoa is a phylum of diverse single-celled eukaryotes. They lack shared morphological characteristics at the microscopic level, and are instead defined by molecular phylogenies of rRNA and actin or polyubiquitin. They were the first major eu ...
: plasmodiophoromycetes (zoospores and gametes),
chlorarachniophyte The chlorarachniophytes are a small group of exclusively marine algae widely distributed in tropical and temperate waters. They are typically mixotrophic, ingesting bacteria and smaller protists as well as conducting photosynthesis. Normally the ...
s (zoospores) *
Amoebozoa Amoebozoa is a major taxonomic group containing about 2,400 described species of amoeboid protists, often possessing blunt, fingerlike, lobose pseudopods and tubular mitochondrial cristae. In traditional and currently no longer supported classi ...
:
myxogastrid Myxogastria/Myxogastrea (myxogastrids, ICZN) or Myxomycetes ( ICN), is a class of slime molds that contains 5 orders, 14 families, 62 genera, and 888 species. They are colloquially known as the ''plasmodial'' or ''acellular' ...
s * Opisthokonta: most metazoans (male gametes, epithelia and choanocytes),
chytrid Chytridiomycota are a division of zoosporic organisms in the kingdom Fungi, informally known as chytrids. The name is derived from the Ancient Greek ('), meaning "little pot", describing the structure containing unreleased zoöspores. Chytrid ...
fungi (zoospores and gametes) * Excavata: some acrasids (''Pocheina'', as zoospores)


Flagellates as organisms: the Flagellata

In older classifications, flagellated
protozoa Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histo ...
were grouped in Flagellata (= Mastigophora), sometimes divided into Phytoflagellata (= Phytomastigina, mostly autotrophic) and Zooflagellata (= Zoomastigina, heterotrophic). They were sometimes grouped with
Sarcodina An amoeba (; less commonly spelled ameba or amœba; plural ''am(o)ebas'' or ''am(o)ebae'' ), often called an amoeboid, is a type of cell or unicellular organism with the ability to alter its shape, primarily by extending and retracting pseudopo ...
(ameboids) in the group
Sarcomastigophora The phylum Sarcomastigophora belongs to the Protista or protoctista kingdom and it includes many unicellular or colonial, autotrophic, or heterotrophic organisms. It is characterized by flagellae, pseudopodia, or both. Taxonomy It is divided in ...
. The autotrophic flagellates were grouped similarly to the botanical schemes used for the corresponding algae groups. The colourless flagellates were customary grouped in three groups, highly artificial: * Protomastigineae, in which absorption of food-particles in holozoic nutrition occurs at a localised point of the cell surface, often at a cytostome, although many groups were merely saprophytes; it included the majority of colourless flagellates, and even many "apochlorotic" algae; * Pantostomatineae (or Rhizomastigineae), in which the absorption takes place at any point on the cell surface; roughly corresponds to "amoeboflagellates"; * Distomatineae, a group of binucleate "double individuals" with symmetrically distributed flagella and, in many species, two symmetrical mouths; roughly corresponds to current Diplomonadida. Presently, these groups are known to be highly polyphyletic. In modern classifications of the protists, the principal flagellated taxa are placed in the following eukaryote groups, which include also non-flagellated forms (A: autotrophic; F: free-living heterotrophic; P: parasitic; S: symbiotic): * Archaeplastida: volvocids (A/F),
prasinophyte The prasinophytes are a group of unicellular green algae. Prasinophytes mainly include marine planktonic species, as well as some freshwater representatives.Sym, S. D. and Pienaar, R. N. 1993. The class Prasinophyceae. In Round, F. E. and Chapman ...
s (A),
glaucophytes The glaucophytes, also known as glaucocystophytes or glaucocystids, are a small group of unicellular algae found in freshwater and moist terrestrial environments, less common today than they were during the Proterozoic. The stated number of spe ...
(A) * Stramenopiles:
bicosoecids Bicosoecida (ICZN) or Bicosoecales/Bicoecea ( ICBN) is an order of Bikosea, a small group of unicellular flagellates, included among the heterokonts. Informally known as bicosoecids, they are a small group of unicellular flagellates. The cells ...
(F), proteromonads (F), opalines (F), most chrysophytes (A/F), part of
xanthophyte Yellow-green algae or the Xanthophyceae (xanthophytes) are an important group of heterokont algae. Most live in fresh water, but some are found in marine and soil habitats. They vary from single-celled flagellates to simple colonial and filament ...
s (A), raphidophytes/chloromonads (A), silicoflagellates (A), ciliophryids (F),
pedinellid Pedinellales is a group of single-celled algae found in both marine environments and freshwater. These are found in both freshwater and marine environments, and most genera are sessile, attached by posterior stalks. The flagellum is at the ante ...
s (A/F) * Alveolata: dinoflagellates (A/F), ''
Colpodella ''Colpodella'' is a genus of alveolates comprising 5 species, and two further possible species: They share all the synapomorphies of apicomplexans, but are free-living, rather than parasitic. Many members of this genus were previously assigned to ...
'' (F) * Rhizaria **
Cercozoa Cercozoa is a phylum of diverse single-celled eukaryotes. They lack shared morphological characteristics at the microscopic level, and are instead defined by molecular phylogenies of rRNA and actin or polyubiquitin. They were the first major eu ...
: cercomonads (F), spongomonads (F), thaumatomonads (F), glissomonads (F), cryomonads (F), heliomonads/dimorphids (F), ebriids (F) *
Amoebozoa Amoebozoa is a major taxonomic group containing about 2,400 described species of amoeboid protists, often possessing blunt, fingerlike, lobose pseudopods and tubular mitochondrial cristae. In traditional and currently no longer supported classi ...
: ''
Multicilia ''Multicilia'' is a flagellated genus of Amoebozoa. It includes the species ''Multicilia marina''.NCBI The National Center for Biotechnology Information (NCBI) is part of the United States National Library of Medicine (NLM), a branch of the ...
'' (F), phalansteriids (F), some
archamoebae The Archamoebae are a group of protists originally thought to have evolved before the acquisition of mitochondria by eukaryotes. They include genera that are internal parasites or commensals of animals (''Entamoeba'' and ''Endolimax''). A few sp ...
(F/S) * Opisthokonta: choanoflagellates (F) * Excavata ** Discoba: jakobids (F),
kinetoplastids Kinetoplastida (or Kinetoplastea, as a class) is a group of flagellated protists belonging to the phylum Euglenozoa, and characterised by the presence of an organelle with a large massed DNA called kinetoplast (hence the name). The organisms are ...
(
bodonid Bodonida is an order of kinetoplastid flagellate excavates. It contains the genera ''Bodo Bodo may refer to: Ethnicity * Boro people, an ethno-linguistic group mainly from Northwest Assam, India * Bodo-Kachari people, an umbrella group fro ...
s, F/P, trypanosomatids, P),
euglenids Euglenids (euglenoids, or euglenophytes, formally Euglenida/Euglenoida, ICZN, or Euglenophyceae, ICBN) are one of the best-known groups of flagellates, which are excavate eukaryotes of the phylum Euglenophyta and their cell structure is typical ...
(F/A), some heteroloboseans (P/F/S) ** Metamonada:
diplomonads The diplomonads (Greek for "two units") are a group of flagellates, most of which are parasitic. They include ''Giardia duodenalis'', which causes giardiasis in humans. They are placed among the metamonads, and appear to be particularly close r ...
(P/F),
retortamonad The retortamonads are a small group of flagellates, most commonly found in the intestines of animals as commensals, although a free-living species called the ''Chilomastix cuspidata'' exists. They are grouped under the taxon, Archezoa. They ar ...
s (S), Preaxostyla/anaeromonads ( oxymonads, S, '' Trimastix'', F),
parabasalid The parabasalids are a group of flagellated protists within the supergroup Excavata. Most of these eukaryotic organisms form a symbiotic relationship in animals. These include a variety of forms found in the intestines of termites and cockroaches ...
s ( trichomonads, P/S,
hypermastigid Hypermastigia (hypermastigids) within microbiology, is the name used for a group of flagellate parasites which were placed under the excavata class. They are now treated as belonging to one of the groups Tritrichomonadea, Hypotrichomonadea, or ...
s, S) *
Eukaryota Eukaryotes () are organisms whose Cell (biology), cells have a cell nucleus, nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the ...
incertae sedis : haptophytes (F/A), cryptophytes (F/A), kathablepharids (F),
Apusozoa The Apusozoa are an Obazoa phylum comprising several genera of flagellate eukaryotes. They are usually around 5–20 μm in size, and occur in soils and aquatic habitats, where they feed on bacteria. They are grouped together based on the prese ...
( apusomondas, F,
ancyromonads Ancyromonadida or Planomonadida is a small group of biflagellated protists found in the soil and in aquatic habitats, where they feed on bacteria.Cavalier-Smith, T. (2013)Early evolution of eukaryote feeding modes, cell structural diversity, and ...
, F, spironemids/hemimastigids, F), collodictyonids/diphylleids (F), '' Phyllomonas'' (F), and about a hundred genera Although the taxonomic group Flagellata was abandoned, the term "flagellate" is still used as the description of a level of organization and also as an ecological functional group. Another term used is "monadoid", from monad. as in ''
Monas The National Monument ( id, Monumen Nasional, abbreviated Monas) is a 132 m (433 ft) obelisk in the centre of Merdeka Square, Central Jakarta, symbolizing the fight for Indonesia. It is the national monument of the Republic of Indones ...
'', and '' Cryptomonas'' and in the groups as listed above. The amoeboflagellates (e.g., the rhizarian genus ''
Cercomonas Cercomonads are small flagellates, widespread in aqueous habitats and common in soils. Characteristics The cells are generally around 10 μm in length, without any shell or covering. They produce filose pseudopods to capture bacteria, but do n ...
'', some amoebozoan
Archamoebae The Archamoebae are a group of protists originally thought to have evolved before the acquisition of mitochondria by eukaryotes. They include genera that are internal parasites or commensals of animals (''Entamoeba'' and ''Endolimax''). A few sp ...
, some excavate Heterolobosea) have a peculiar type of flagellate/ amoeboid organization, in which cells may present flagella and pseudopods, simultaneously or sequentially, while the helioflagellates (e.g., the cercozoan heliomonads/dimorphids, the stramenopile
pedinellid Pedinellales is a group of single-celled algae found in both marine environments and freshwater. These are found in both freshwater and marine environments, and most genera are sessile, attached by posterior stalks. The flagellum is at the ante ...
s and ciliophryids) have a flagellate/ heliozoan organization.Mikryukov, K.A. (2001). Heliozoa as a component of marine microbenthos: a study of Heliozoa of the White Sea. ''Ophelia'' 54: 51–73.


References


External links

* * Leadbeater, B.S.C. & Green, J.C., eds. (2000). ''The Flagellates. Unity, diversity and evolution''. Taylor and Francis, London. * {{Authority control Cell biology Microbiology