Euglenozoa
Encyclopedia
The Euglenozoa are a large group of flagellate
protozoa
. They include a variety of common free-living species, as well as a few important parasites, some of which infect humans. There are two main subgroups, the euglenid
s and kinetoplastid
s. Euglenozoa are unicellular, mostly around 15-40 µm
in size, although some euglenids get up to 500 µm long.
or mouth, used to ingest bacteria
or other small organisms. This is supported by one of three sets of microtubule
s that arise from the flagellar bases; the other two support the dorsal and ventral surfaces of the cell.
Some other euglenozoa feed through the absorption, and many euglenids possess chloroplast
s and so obtain energy through photosynthesis
. These chloroplasts are surrounded by three membranes and contain chlorophyll
s A and C, along with other pigments, so are probably derived from a captured green alga. Reproduction occurs exclusively through cell division. During mitosis
, the nuclear membrane remains intact, and the spindle microtubules form inside of it.
The group is characterized by the ultrastructure of the flagella. In addition to the normal supporting microtubules or axoneme
, each contains a rod (called paraxonemal), which has a tubular structure in one flagellum and a latticed structure in the other. Based on this, two smaller groups have been included here: the diplonemids and Postgaardi
.
; the two share mitochondria with disk-shaped cristae, which only occurs in a few other groups. Both probably belong to a larger group of eukaryotes called the excavate
s. This grouping, though, has been challenged.
Flagellate
Flagellates are organisms 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, some gymnosperms and other closely related plants...
protozoa
Protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...
. They include a variety of common free-living species, as well as a few important parasites, some of which infect humans. There are two main subgroups, the euglenid
Euglenid
Euglenoids are one of the best-known groups of flagellates, commonly found in freshwater especially when it is rich in organic materials, with a few marine and endosymbiotic members. Most euglenids are unicellular. Many euglenids have chloroplasts and produce energy through photosynthesis, but...
s and kinetoplastid
Kinetoplastid
The kinetoplastids are a group of single-cell flagellate protozoa, including a number of parasites responsible for serious diseases in humans and other animals, as well as various forms found in soil and aquatic environments...
s. Euglenozoa are unicellular, mostly around 15-40 µm
1 E-5 m
To help compare different orders of magnitude, this page lists lengths between 10−5 m and 10−4 m .Distances shorter than 10 µm* 10 µm — width of cotton fibre...
in size, although some euglenids get up to 500 µm long.
Structure
Most euglenozoa have two flagella, which are inserted parallel to one another in an apical or subapical pocket. In some these are associated with a cytostomeCytostome
A cytostome 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 vacuoles. Only certain groups of protozoa, such as the ciliates and excavates, have cytostomes. Such...
or mouth, used to ingest bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
or other small organisms. This is supported by one of three sets of microtubule
Microtubule
Microtubules are a component of the cytoskeleton. These rope-like polymers of tubulin can grow as long as 25 micrometers and are highly dynamic. The outer diameter of microtubule is about 25 nm. Microtubules are important for maintaining cell structure, providing platforms for intracellular...
s that arise from the flagellar bases; the other two support the dorsal and ventral surfaces of the cell.
Some other euglenozoa feed through the absorption, and many euglenids possess chloroplast
Chloroplast
Chloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.Chloroplasts are green...
s and so obtain energy through photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
. These chloroplasts are surrounded by three membranes and contain chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
s A and C, along with other pigments, so are probably derived from a captured green alga. Reproduction occurs exclusively through cell division. During mitosis
Mitosis
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...
, the nuclear membrane remains intact, and the spindle microtubules form inside of it.
The group is characterized by the ultrastructure of the flagella. In addition to the normal supporting microtubules or axoneme
Axoneme
Numerous eukaryotic cells carry whip-like appendages whose inner core consists of a cytoskeletal structure called the axoneme....
, each contains a rod (called paraxonemal), which has a tubular structure in one flagellum and a latticed structure in the other. Based on this, two smaller groups have been included here: the diplonemids and Postgaardi
Postgaardi
Postgaardi mariagerensis is a species of single-celled eukaryote in the Euglenozoa. Some have classified it in a class called Postgaardea along with Calkinsia, but as of 2009, Postgaardi is not well enough known to confidently determine its relationship with other organisms in the Euglenozoa...
.
Classification
The euglenozoa are generally accepted as monophyletic. They are related to PercolozoaPercolozoa
The Percolozoa are a group of colourless protozoa, including many that can transform between amoeboid, flagellate, and encysted stages.-Terminology and classification:...
; the two share mitochondria with disk-shaped cristae, which only occurs in a few other groups. Both probably belong to a larger group of eukaryotes called the excavate
Excavate
The excavates are a major kingdom of unicellular eukaryotes, often known as Excavata. The phylogenetic category Excavata, proposed by Cavalier-Smith in 2002, contains a variety of free-living and symbiotic forms, and also includes some important parasites of humans.-Characteristics:Many excavates...
s. This grouping, though, has been challenged.