Flagellate

Not to be confused with flagellation or fellate.

This article is about eukaryotic flagellates. For bacterial flagella and their differences, see Flagellum.

"Flagellata" from Encyclopædia Britannica

"Flagellata" from Ernst Haeckel's Artforms of Nature, 1904

File:Giardia lamblia.jpg

Parasitic excavate (Giardia lamblia)

Green alga (Chlamydomonas)

A flagellate is a cell or organism with one or more whip-like organelles called flagella. The word flagellate also describes a particular construction (or level of organization) characteristic of many protists (eukaryotic organisms) and their means of motion. The term presently does not imply any specific relationship or classification of the organisms that possess flagellae. However, the term "flagellate" is included in other terms (such as "dinoflagellate" and "choanoflagellata") which are more formally characterized.

Form and behavior

Eukaryotic flagella are supported by microtubules 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 or mouth, where food is ingested. Flagella often support hairs, called mastigonemes, or contain rods. Their ultrastructure plays an important role in classifying eukaryotes.

Among protoctists and microscopic animals, a flagellate is an organism with one or more whip-like organelles called flagella. Some cells in animals may be flagellate, for instance the spermatozoa of most 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 things, 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, and Choanozoa, which make up a group called the opisthokonts, there is a single posterior flagellum. They are from the phylum Mastigophora. They can cause diseases and they can make their own food. 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

Some cells in animals may be flagellate, for instance the spermatozoa of most phyla, or the choanocytes of sponges. Flowering plants do not produce flagellate cells, but ferns, mosses, green algae, some gymnosperms and other closely related plants do. Likewise, most fungi do not produce cells with flagellae, but the primitive fungal chytrids do. For more examples of flagellated cells as specialized cells of multicellular organisms or as life cycle stages, see flagellum.

Flagellates as organisms: the Flagellata

In older classifications, some protozoa were grouped in Flagellata (= Mastigophora), sometimes divided in Phytoflagellata (= Phytomastigina) and Zooflagellata (= Zoomastigina). They were sometimes grouped with Sarcodina (ameboids) in Sarcomastigophora.

Modern classifications place these example genera into the following groups (see Kudo, 1954 and Cavalier-Smith, 2000):

Genera	Newer classification	Older classification
Multicilia, Mastigamoeba, Phalansterium	Amoebozoa	Zoomastigina
Ancyromonas	Apusozoa	Zoomastigina
Cercomonas	Rhizaria	Zoomastigina
Trypanosoma, Bodo, Oxymonas, Giardia, Trichomonas	Excavata	Zoomastigina
Bicosoeca	Chromalveolata > Heterokontophyta > Bicosoecea	Zoomastigina
Salpingoeca, Codosiga	Opisthokonta > Choanoflagellata	Zoomastigina
Cryptomonas	Chromalveolata > Cryptophyta	Phytomastigina
Pontosphaera	Chromalveolata > Haptophyta	Phytomastigina
Chromulina, Synura	Chromalveolata > Heterokontophyta	Phytomastigina
Prorocentrum, Peridinium	Chromalveolata > Alveolata > Dinophyta	Phytomastigina
Chlamydomonas, Volvox, Nephroselmis	Archaeplastida > Viridiplantae > Chlorophyta	Phytomastigina
Euglena	Excavata > Euglenozoa	Phytomastigina

Although the taxonomic group Flagellata was abandoned, the term "flagellate" remains valid as the description of a level of organization. Amoeboflagellates (e.g., some Heterolobosea, Mastigamoeba, Pelomyxa, Cercomonas) have a peculiar type of flagellate/amoeboid organization, in which cells may present flagella and pseudopods, simultaneously or sequentially.

External links

• Flagellata at the US National Library of Medicine Medical Subject Headings (MeSH)
• Jeuck, A., & Arndt, H. (2013). A short guide to common heterotrophic flagellates of freshwater habitats based on the morphology of living organisms. Protist, 164 (6): 842-860, [1].
• Leadbeater, B.S.C. & Green, J.C., eds. (2000). The Flagellates. Unity, diversity and evolution. Taylor and Francis, London.