| Asterionella | |
|---|---|
 | |
| Asterionella formosa | |
Scientific classification  | |
| Domain: | Eukaryota |
| Clade: | Diaphoretickes |
| Clade: | SAR |
| Clade: | Stramenopiles |
| Phylum: | Gyrista |
| Subphylum: | Ochrophytina |
| Class: | Bacillariophyceae |
| Order: | Fragilariales |
| Family: | Fragilariaceae |
| Genus: | Asterionella A.H. Hassall (1850) |
| Species | |
See text | |
Asterionella is a genus of pennate freshwater diatoms. They are frequently found in star-shaped colonies of individuals.
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.
The silica skeleton of a diatom cell (called the frustule) consists of an epitheca and an hypotheca. 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. [1]
Asterionella formosa is known to be susceptible to the chytrid fungus Zygorhizidium planktonicum. [2] [3] 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. [4] Asterionella have no means of locomotion. It is most likely a combination of gravity and currents that distribute the organism.
Asterionella bleakeleyi
Asterionella candelabrum
Asterionella formosa
Asterionella madagascariensis
Chytridiomycota are a division of zoosporic organisms in the kingdom Fungi, informally known as chytrids. The name is derived from the Ancient Greek χυτρίδιον (khutrídion), meaning "little pot", describing the structure containing unreleased zoospores. Chytrids are one of the earliest diverging fungal lineages, and their membership in kingdom Fungi is demonstrated with chitin cell walls, a posterior whiplash flagellum, absorptive nutrition, use of glycogen as an energy storage compound, and synthesis of lysine by the α-amino adipic acid (AAA) pathway.
A resting spore is a resistant cell, used to survive adverse environmental conditions. Resting spore is a term commonly applied to both diatoms and fungi.
Rhizophydiales are an important group of chytrid fungi. They are found in soil as well as marine and fresh water habitats where they function as parasites and decomposers.
Selenastraceae is a family of green algae in the order Sphaeropleales. Members of this family are common components of the phytoplankton in freshwater habitats worldwide. A few species have been found in brackish and marine habitats, such as in the Baltic Sea.
Eudorina is a paraphyletic genus in the volvocine green algae clade. Eudorina colonies consist of 16, 32 or 64 individual cells grouped together. Each individual cell contains flagella which allow the colony to move as a whole when the individual cells beat their flagella together. Description by GM Smith :
Ankistrodesmus is a genus of green algae in the family Selenastraceae. It is one of the most common types of phytoplankton in freshwater habitats around the world.
Monactinus is a genus of green algae in the family Hydrodictyaceae. It is very common in freshwater regions throughout the world.
Parapediastrum is a genus of green algae in the family Hydrodictyaceae. It is fairly common in freshwater regions throughout the world.
Podohedriella is a genus of green algae in the family Selenastraceae. It is found in freshwater habitats or on damp wood.
Pseudopediastrum is a genus of green algae in the family Hydrodictyaceae. It is very common in freshwater regions throughout the world.
Selenastrum is a genus of green algae in the family Selenastraceae. It is common in freshwater habitats around the world. Most species prefer temperate or warm-temperate waters.
Stauridium is a genus of green algae in the family Hydrodictyaceae. It is very common in freshwater regions throughout the world.
Polarella is a dinoflagellate, and is the only extant genus of the Suessiaceae family. The genus was described in 1999 by Marina Montresor, Gabriele Procaccini, and Diane K. Stoecker, and contains only one species, Polarella glacialis. Polarella inhabits channels within ice formations in both the Arctic and Antarctic polar regions, where it plays an important role as a primary producer. Polarella is a thecate dinoflagellate, wherein the cell has an outer covering of cellulose plates, which are arranged in nine latitudinal series. The general morphology of Polarella is similar to that of a typical dinoflagellate. and Polarella has a zygotic life history, wherein it alternates between a motile vegetative phase and a non-motile spiny cyst. While it is thought that the cysts of Polarella have lost their ability to form fossils, the cyst life cycle stage has acted as link to extinct members of the Suessiaceae family.
Pediastrum duplex is a species of fresh water green algae in the genus Pediastrum. It is the type species of the genus Pediastrum.
Hildenbrandia is a genus of thalloid red alga comprising about 26 species. The slow-growing, non-mineralized thalli take a crustose form. Hildenbrandia reproduces by means of conceptacles and produces tetraspores.
Skeletonema dohrnii is a diatom. Together with S. marinoi, this species has flattened extremities of the processes of the fultoportulae, which interlock with those of succeeding valves without forming knuckles. It is a species of the genus Skeletonema that can be found in many waters across the globe. In the coastal waters of South Korea, their cell diameters are about 3 to 6 micrometers.
Coolia is a marine dinoflagellate genus in the family Ostreopsidaceae. It was first described by Meunier in 1919. There are currently seven identified species distributed globally in tropical and temperate coastal waters. Coolia is a benthic or epiphytic type dinoflagellate: it can be found adhered to sediment or other organisms but it is not limited to these substrates. It can also be found in a freely motile form in the water column. The life cycle of Coolia involves an asexual stage where the cell divides by binary fission and a sexual stage where cysts are produced. Some of the species, for example, Coolia tropicalis and Coolia malayensis, produce toxins that can potentially cause shellfish poisoning in humans.
Asterionella formosa is a species of diatom belonging to the family Fragilariaceae.
Ethmodiscus is a genus of diatoms found widely scattered throughout the intertropical and temperate zones in the world's oceans. The large diatom genus can get up to 2mm in size, and it has distinct cell features like a vacuole that comprises over 99% of its cell's volume. Despite their large size, they are known to be in open oceans in low quantity. While in the ocean, Ethmodiscus use buoyancy control to migrate up and down to the high nitrogen depths and return to the surface to photosynthesize. Additionally, the biological characteristics of Ethmodiscus are an important component in interpreting deep-sea sedimentary richness and distribution.
Phytoplankton are characterized as organisms which are unable to swim against a current and produce their own organic carbon via photosynthesis. They are responsible for producing approximately 50 percent of the Earth’s primary productivity and are therefore crucial in maintaining both marine ecosystems and adding a significant amount of oxygen to the atmosphere. However, as with other organisms, phytoplankton are hosts to many diverse forms of parasites, including, but not limited to, fungal- and non-fungal zoosporic parasites, Dinoflagellates, Cercozoans, and viruses. Parasites use nutrients from their hosts, at that organisms expense, and display diverse methods of infection. Parasites can play integral roles in the dynamics and interactions between phytoplankton and their communities, such as controlling population abundance, distribution and biodiversity.
Mekhalfi, Malika; Amara, Sawsan; Robert, Sylvie (June 2014). "Effect of environmental conditions on various enzyme activities and triacylglycerol contents in cultures of the freshwater diatom, Asterionella forrnosa (Bacillariophyceae)". Biochimie. 101: 21–30. doi:10.1016/j.biochi.2013.12.004. PMID 24355202.Maier, Michelle A.; Peterson, Tawnya D. (Oct 2014). "Observations of a Diatom Chytrid Parasite in the Lower Columbia River". Northwest Science. 88 (3): 234–245. doi:10.3955/046.088.0306.