''Asterionella'' is a genus of
pennate
Pinnation (also called pennation) is the arrangement of feather-like or multi-divided features arising from both sides of a common axis. Pinnation occurs in biological morphology, in crystals, such as some forms of ice or metal crystals, and in ...
freshwater
Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...
diatom
A diatom (Neo-Latin ''diatoma'') is any member of a large group comprising several Genus, genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of Earth's B ...
s. They are frequently found in star-shaped colonies of individuals.
Description
''Asterionella'' average cell size is 60–85 micrometers long and 2–4 micrometers wide.
It forms colonies that often consist of eight cells, but can vary up to 20 cells. The cells in the colony are attached by the apex by extracellular matter. By the way the cells are attached to each other, the colonies often look like stars or spiralling chains.
Reproduction
The silica skeleton of a diatom cell (called the
frustule
A frustule is the hard and porous cell wall or external layer of diatoms. The frustule is composed almost purely of silica, made from silicic acid, and is coated with a layer of organic substance, which was referred to in the early literature on ...
) consists of an
epitheca
''Epitheca'' is a genus of Odonata, dragonflies in the family (biology), family Corduliidae. They are commonly known as baskettails. Baskettails' distinction is the specially adapted, upturned abdomen tip of the females which allows them to carr ...
and an
hypotheca
Hypotheca may refer to:
* The inner Frustule#Thecae, theca of the frustule (exoskeleton) of a diatom
* Hypothec, in civil law, a sort of mortgage
{{disambiguation ...
. The hypotheca is slightly smaller than the epitheca. During asexual reproduction both thecae form the epitheca of the new daughter cell and each daughter produces a new hypotheca. Therefore one daughter cell is always smaller than the original cell.
In order to regain their original size, it is usually assumed diatoms have to reproduce sexually, although this has not yet been observed in A. formosa. However, there may also be other ways to rejuvenate.
Ecology
''Asterionella formosa'' is known to be susceptible to the
chytrid
Chytridiomycota are a division of zoosporic organisms in the kingdom (biology), kingdom Fungi, informally known as chytrids. The name is derived from the Ancient Greek ('), meaning "little pot", describing the structure containing unreleased zo ...
fungus ''Zygorhizidium planktonicum''. If a chytrid attaches to an ''Asterionella'' cell, they can, however, protect others of their kind by committing apoptosis, or cellular suicide, stopping the spread of the parasite. This is called a hypersensitive reaction.
[''The Existence of a Hypersensitive Reaction in the Planktonic Diatom Asterionella Formosa'', Cantor et al. 1978, New Phytologist. 82p187-206.] ''Asterionella'' have no means of locomotion. It is most likely a combination of gravity and currents that distribute the organism.
Species
''
Asterionella bleakeleyi
''Asterionella'' is a genus of pennate freshwater diatoms. They are frequently found in star-shaped colonies of individuals.
Description
''Asterionella'' average cell size is 60–85 micrometers long and 2–4 micrometers wide.
It forms coloni ...
''
''
Asterionella candelabrum
''Asterionella'' is a genus of pennate freshwater diatoms. They are frequently found in star-shaped colonies of individuals.
Description
''Asterionella'' average cell size is 60–85 micrometers long and 2–4 micrometers wide.
It forms coloni ...
''
''
Asterionella formosa
''Asterionella formosa'' is a species of diatom belonging to the family Fragilariaceae.
It has cosmopolitan distribution.
Taxonomy
''Asterionella formosa'' is the type species of its genus, '' Asterionella''.
Etymology
The species name "''fo ...
''
''
Asterionella madagascariensis
''Asterionella'' is a genus of pennate freshwater diatoms. They are frequently found in star-shaped colonies of individuals.
Description
''Asterionella'' average cell size is 60–85 micrometers long and 2–4 micrometers wide.
It forms coloni ...
''
References
Further reading
External links
*
{{Taxonbar, from=Q150125
Diatom genera
Fragilariophyceae