Note

The flagellates are a grade of organisation. Traditionally, they are those protozoa which spend most of their existence moving or feeding with a small number of flagella. This type of organization is the most widespread among protists. Of the 60 lineages of protists identified among the eukaryotes, 27 satisfy the condition of being a protozoan flagellate. In addition, alveolates and stramenopiles include heterotrophic flagellates, as do several groups often thought of as algae (dinoflagellates, euglenids, and cryptomonads). Some of the amoebae revert to flagellated forms for part of their life history or have non-functional flagella attached to their bodies.

Many parasites which affect human health or economy are flagellates. They include the relatively benign Giardia and the more damaging trypanosomes and leishmaniases. Flagellates are the major consumers of primary and secondary production in aquatic ecosystems - consuming bacteria and other protists and ensuring the recycling of limiting nutrients.

A variety of marine flagellates from the genera (left to right) Cryptaulax, Abollifer, Bodo, Rhynchomonas, Kittoksia, Allas, and Metromonas.
Drawings by Naja Voers.

Flagella arose early in eukaryote evolution, and we are not able to identify any groups of protists which are primitively without flagella.

Eukaryotic flagella are not the same as flagella of bacteria. They have an internal structure comprised of nine doublets of microtubules forming a cylinder around a central pair of microtubules. The peripheral doublets are linked to each other by proteins. These proteins include dynein, a molecular motor which can cause flagella to bend and propel the cell relative to its environment, or propel water or mucus relative to the cell. Many protists have embellishments within or on the outer surface of the flagellum (see electron-micrographs below ). There may be one, two or many flagella. Flagella in rows are said to occur in kineties. Cilia of ciliates and metazoa are a special type of flagellum, organized such that many flagella in kineties (= cilia) may work in synchrony.

Ploeotia (Euglenozoa, Euglenida, a heterotrophic euglenid common in marine sediments, showing anterior (to the left) and posterior flagella. Flagella in euglenids are thicker than in many other eukaryotes because of the presence of an additional rod within the flagellum (the crystalline structure within the flagellum to the right below), and because there is a thick coating of fine hairs on the outside.

Electron micrographs of Chilomastix cuspidata (excavates, retortamonads) and of Entosiphon sulcatum (Euglenozoa, Euglenida). The "9+2" axoneme and the enclosing membrane can be seen in both micrographs, the flagellum of Chilomastix has two vanes, and that of Entosiphon has a crystalline structure lying alongside the axoneme.

The flagellated body form is the most widely exploited among the eukaryotes. The tables below summarise the diversity of HETEROTROPHIC flagellates, and further flagellated taxa are encountered in some of the algal groups

Groups of Flagellates

GROUP	CIRCUMSCRIPTION - EXAMPLES	HABITAT OF FREE-LIVING SPECIES	FOOD OF FREE-LIVING SPECIES	PARASITE?
Ancyromonas	genus of heterotrophic flagellates	marine, freshwater and terrestrial	bacteria	free-living
Apusomonads	several genera of heterotrophic flagellates, Apusomonas, Amastigomonas	marine, freshwater and terrestrial	bacteria	free-living
Cercomonads	several genera of heterotrophic flagellates, Cercomonas, Heteromita, Massisteria	marine, freshwater and terrestrial	bacteria	free-living
Collodictyon	genus of heterotrophic flagellates	free-living	protists	free-living
Cryothecomonas	genus of heterotrophic flagellates	marine	bacteria?	free-living
Dimorphids	several genera of heliozoon-like flagellates, Dimorpha, Tetradimorpha	marine, freshwater	bacteria	free-living
Diphylleia	genus of heterotrophic flagellates	freshwater	protists	free-living
Discocelis	genus of heterotrophic flagellates	marine	osmotrophic, bacteria	free-living
Ebriids	several genera of heterotrophic flagellates, ebria, Hermesinum	marine	protists	free-living
Excavates	flagellates, diplomonads, jakobids, retortamonads, Trimastix, Carpedediemonas, heterolobosea, etc.	marine, freshwater, terrestrial	bacteria	free-living and parasites
Euglenozoa	flagellates, euglenids and kinetoplastids, Peranema, Bodo	marine, freshwater, terrestrial	bacteria, protists, detritus	free-living, a few parasites
Hamates	Caecitellus and psedodendromonads (Pseudodendromonas, Cyathomonas), related to stramenopiles	marine, freshwater	bacteria	free-living
Kathablepharids	several genera of heterotrophic flagellates	marine, freshwater	bacteria, protists	free-living
Ministeria	genus of heterotrophic flagellates	marine	osmotrophic, bacteria	free-living
Multicilia	genus of heterotrophic flagellates	marine and freshwater	bacteria, protists	free-living
Oxymonads	several genera of heterotrophic flagellates, Oxymonas			endobionts
Parabasalids	several genera of parasitic heterotrophic flagellate, Trichomonas	free-living taxa in marine, soils and freshwater habitats		mostly endobionts, but a few free-living
Pelobionts	several genera of amitochondriate flagellates	marine, freshwater, soils	osmotrophic, bacteria, detritus	free-living, a few parasites
Phalansterium	genus of heterotrophic flagellates	freshwater	bacteria	free-living
Plasmodiophorids	parasitic flagellates	freshwater, soils		pathogenic
Spironemids	several genera of heterotrophic flagellates, Spironema, Hemimastix, Stereonema	freshwater, soils	bacteria	free-living
Spongomonads	several genera of heterotrophic flagellates, Spongomonas, Rhipidodendron	freshwater, soils	bacteria	free-living
Stephanopogon	genus of heterotrophic flagellates	marine	bacteria, detritus, protists	free-living
Telonema	genus of heterotrophic flagellates	marine	protists	predatory
Thaumatomonads	several genera of heterotrophic flagellates, Thaumatomastix, Protaspis	freshwater, marine, soils	bacteria, detritus, protists	free-living

Heterotrophic flagellates are also found in the following taxa:

Alveolates	heterotrophic dinoflagellates Colpodella	freshwater and marine	bacteria, other protists	free-living, parasitic and syymbiotic
Cryptomonads	Goniomonas and Chilomonas	freshwater, soils and marine	bacteria, osmotrophs	free-living only
Opisthokonts	Choanoflagellates	freshwater, soils, marine	bacteria	free-living only
Stramenopiles	bicosoecids, proteromonads, opalines, heterotrophic chrysophytes, pedinellids	freshwater and marine	bacteria, osmotrophs	free-living and parasitic
Viridaeplantae	Polytoma, Polytomella and a few other genera	freshwater	osmotrophs	free-living

Genera of flagellates for which ultrastructural studies have yet to be carried out, and whose ultrastructural identity is therefore still unknown (after Patterson, 1999)

Acinetactis Allantion Allas Alphamonas Amphimonas Artodiscus Aulomonas Bodomorpha Bodopsis Bordnamonas Campanoeca Cladomonas

Clautriavia Codonoeca Cruzella Cyathomonas Cyclomonas Dallingeria Dimastigamoeba Dingensia Dinoasteromonas Dinomonas Diplocalium Diplomita

Diploselmis Errera Fromentella Heliobodo Kamera Kiitoksia Macappella Metopion Metromonas Microcometes Micromonas Monochrysis

Parabodo Paramastix Paramonas Peltomonas Phanerobia Phloxamoeba Phyllomitus Phyllomonas Platytheca Pleurostomum Quadricilia Proleptomonas

Rhizomonas Rigidomastix Sainouron Salpingorhiza Schewiakoffia Stenocodon Stephanomonas Toshiba Trichonema

References

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