| Hemiselmis | |
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| Hemiselmis, illustration | |
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| Genus: | Hemiselmis Parke 1949 |
| Type species | |
| Hemiselmis rufescens Parke 1949 | |
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Hemiselmis is a genus of cryptomonads. [1]
| Hemiselmis | |
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| Hemiselmis, illustration | |
| Scientific classification | |
| Domain: | |
| Phylum: | |
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| Genus: | Hemiselmis Parke 1949 |
| Type species | |
| Hemiselmis rufescens Parke 1949 | |
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Hemiselmis is a genus of cryptomonads. [1]
It was first described by English biologist Mary Parke in 1949. [1] She also described the first species in this genus, Hemiselmis rufescens. [1]
Hemiselmis are typically 4 to 9 micrometers long, free-swimming, biflagellate monads. [1] They are generally bean-shaped with the flagella located between 1/3 and 1/2 the cell length from the anterior. [2] A tubular gullet lined with usually two rows of ejectisomes is found to be in the posterior region of the cell. A single plastid and nucleomorph are present, with it possessing the biliprotein pigment Cr-phycoerythrin 555 or one of Cr-phycocyanin, 577, 612 and 630. [3] [4] For example, Hemiselmis pacifica possesses Cr-PC577, and Cr-PC612 is found in Hemiselmis virescens and Hemiselmis tepida. [4] The chloroplasts are red in color. [5]
The species has periplast surrounding the cells below plasma membrane. [1] The periplast consists of internal and superficial plates that have a general shape of hexagons. [1] The ultrastructure of several species is well known. The periplast of H. brunnescens has crystalline plates and an unusual secondary layer composed of small "sausage-like" fibrils. [1] The nucleomorph is located outside the pyrenoid between the pyrenoid and the nucleus. [6] The flagella are covered with a layer of fibrillary scales overlapping with each other. [7] Serial reconstruction has shown that there is only one mitochondrion per cell. [7]
Reproduction is only known by asexual reproduction. [1] Species of Hemiselmis remain motile even while dividing. [1]
Hemiselmis species may easily be overlooked in samples due to their small size and rapid movement, but can be recognized by the special corkscrew swimming motion. [1] It is concluded that the spiral swimming is not because of the irregularity in length or structure of flagella, but because of the dorsoventral flattening of its body. Also, the fact that the flagella are attached at a low point near posterior contributed to the unique swimming pattern observed. [1]
Species are generally found in oceanic or coastal marine waters. [7] They are also found in freshwater environment. [2] They are found in a variety of locations on Earth. The locations include Baltic Sea, Caribbean Sea and Isle of Man. [7] Specific temperature ranges and depths to find these species are still not yet classified.
The nucleomorph genome of H. rufescens has been studied quite thoroughly. Using pulsed-field gel electrophoresis (PFGE), size of the H. rufescens nucleomorph genome was estimated to be 580 kb. [5]
The most significant discovery so far is the complete sequence of nucleomorph genome of Hemiselmis andersenii. The size of the genome is 0.572 Mbp. [6] The nucleomorph genome shows a complete intron loss, with no spliceosomal introns and genes for splicing RNAs. [6] It is suggested that evolution has driven the loss of introns and modified the shape and function of proteins; minimal functional units are needed to maintain basic eukaryotic cellular processes. [6]
There are currently 16 identified species. Of the 16 species, 14 are accepted taxonomically. [7] Currently, Hemiselmis brunnescens and Hemiselmis cyclopea have unknown status. [7]
A complete list is added below.
Hemiselmis amylifera Butcher, 1967
Hemiselmis amylosa Clay & Kugrens, 1999
Hemiselmis andersenii Lane & Archibald, 2008
Hemiselmis anomala Butcher, 1967
Hemiselmis brunnescens Butcher, 1967
Hemiselmis cryptochromatica Lane & Archibald, 2008
Hemiselmis cyclopea Butcher, 1967
Hemiselmis oculata Butcher, 1967
Hemiselmis pacifica Lane & Archibald, 2008
Hemiselmis parvula (Skuja) Butcher, 1967
Hemiselmis rotunda Butcher, 1967
Hemiselmis rufescens Parke, 1949
Hemiselmis simplex Butcher, 1967
Hemiselmis tepida Lane & Archibald, 2008
Hemiselmis vinosa (Conrad) Chrétiennot-Dinet, 1990
Hemiselmis virescens Droop, 1955
The cryptomonads are a group of algae, most of which have plastids. They are common in freshwater, and also occur in marine and brackish habitats. Each cell is around 10–50 μm in size and flattened in shape, with an anterior groove or pocket. At the edge of the pocket there are typically two slightly unequal flagella.
The chlorarachniophytes are a small group of exclusively marine algae widely distributed in tropical and temperate waters. They are typically mixotrophic, ingesting bacteria and smaller protists as well as conducting photosynthesis. Normally they have the form of small amoebae, with branching cytoplasmic extensions that capture prey and connect the cells together, forming a net. They may also form flagellate zoospores, which characteristically have a single subapical flagellum that spirals backwards around the cell body, and walled coccoid cells.
Cryptomonas is the name-giving genus of the Cryptomonads established by German biologist Christian Gottfried Ehrenberg in 1831. The algae are common in freshwater habitats and brackish water worldwide and often form blooms in greater depths of lakes. The cells are usually brownish or greenish in color and are characteristic of having a slit-like furrow at the anterior. They are not known to produce any toxins. They are used to feed small zooplankton, which is the food source for small fish in fish farms. Many species of Cryptomonas can only be identified by DNA sequencing. Cryptomonas can be found in several marine ecosystems in Australia and South Korea.
Nucleomorphs are small, vestigial eukaryotic nuclei found between the inner and outer pairs of membranes in certain plastids. They are thought to be vestiges of primitive red and green algal nuclei that were engulfed by a larger eukaryote. Because the nucleomorph lies between two sets of membranes, nucleomorphs support the endosymbiotic theory and are evidence that the plastids containing them are complex plastids. Having two sets of membranes indicate that the plastid, a prokaryote, was engulfed by a eukaryote, an alga, which was then engulfed by another eukaryote, the host cell, making the plastid an example of secondary endosymbiosis.
Pandorina is a genus of green algae composed of 8, 16, or sometimes 32 cells, held together at their bases to form a sack globular colony surrounded by mucilage. The cells are ovoid or slightly narrowed at one end to appear keystone- or pear-shaped. Each cell has two flagella with two contractile vacuoles at their base, an eyespot, and a large cup-shaped chloroplast with at least one pyrenoid.
Euglena gracilis is a freshwater species of single-celled alga in the genus Euglena. It has secondary chloroplasts, and is a mixotroph able to feed by photosynthesis or phagocytosis. It has a highly flexible cell surface, allowing it to change shape from a thin cell up to 100 µm long, to a sphere of approximately 20 µm. Each cell has two flagella, only one of which emerges from the flagellar pocket (reservoir) in the anterior of the cell, and can move by swimming, or by so-called "euglenoid" movement across surfaces. E. gracilis has been used extensively in the laboratory as a model organism, particularly for studying cell biology and biochemistry.
Tetraselmis is a genus of phytoplankton. Tetraselmis is a green algal genus within the order Chlorodendrales, and they are characterized by their intensely-colored green chloroplast, their flagellated cell bodies, the presence of a pyrenoid within the chloroplast, and a scale-produced thecal-wall. Species within this genus are found in both marine and freshwater ecosystems across the globe; their habitat range is mainly limited by water depth due to their photosynthetic nature. Thus, they live in diverse water environments if enough nutrients and light are available for net photosynthetic activity. Tetraselmis species have proven to be useful for both research and industry. Tetraselmis species have been studied for understanding plankton growth rates, and recently a colonial species is being used to gain an understanding of multicellularity evolution. Additionally, many species are currently being examined for their use as biofuels due to their high lipid content.
The cryptophyceae are a class of algae, most of which have plastids. About 220 species are known, and they are common in freshwater, and also occur in marine and brackish habitats. Each cell is around 10–50 μm in size and flattened in shape, with an anterior groove or pocket. At the edge of the pocket there are typically two slightly unequal flagella.
Jakobids are an order of free-living, heterotrophic, flagellar eukaryotes in the supergroup Excavata. They are small, and can be found in aerobic and anaerobic environments. The order Jakobida, believed to be monophyletic, consists of only twenty species at present, and was classified as a group in 1993. There is ongoing research into the mitochondrial genomes of jakobids, which are unusually large and bacteria-like, evidence that jakobids may be important to the evolutionary history of eukaryotes.
Rhodomonas is a genus of cryptomonads. It is characterized by its red colour, the square-shaped plates of its inner periplast, its short furrow ending in a gullet, and a distinctly shaped chloroplast closely associated with its nucleomorph. Historically, Rhodomonas was characterized by its red chloroplast alone, but this no longer occurs as its taxonomy has become increasingly based on molecular and cellular data. Currently, there is some debate about the taxonomic validity of Rhodomonas as a genus and further research is needed to verify its taxonomic status. Rhodomonas is typically found in marine environments, although freshwater reports exist. It is commonly used as a live feed for various aquaculture species.
Goniomonas is a genus of Cryptomonads and contains five species. It is a genus of single-celled eukaryotes, including both freshwater and marine species. It lacks plastids, which is very unusual among all of the Cryptophyte genera. It may reflect one of only a small number of times that the Cryptophytes evolved into freshwater habitats. Goniomonas seems to have a number of freshwater relatives which have not yet been cultured and named.
Geminigera /ˌdʒɛmɪnɪˈdʒɛɹə/ is a genus of cryptophyte from the family Geminigeraceae. Named for its unique pyrenoids, Geminigera is a genus with a single mixotrophic species. It was discovered in 1968 and is known for living in very cold temperatures such as under the Antarctic ice. While originally considered to be part of the genus Cryptomonas, the genus Geminigera was officially described in 1991 by D. R. A. Hill.
Guillardia is a genus of flagellate cryptomonad algae belonging to the family Geminigeraceae, containing a secondary plastid within a reduced cytoplasmic compartment that contains a vestigial nucleomorph. There is only one characterised member of this genus, Guillardia theta.
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.
Dinophysis is a genus of dinoflagellates common in tropical, temperate, coastal and oceanic waters. It was first described in 1839 by Christian Gottfried Ehrenberg.
Mesodinium chamaeleon is a ciliate of the genus Mesodinium. It is known for being able to consume and maintain algae endosymbiotically for days before digesting the algae. It has the ability to eat red and green algae, and afterwards using the chlorophyll granules from the algae to generate energy, turning itself from being a heterotroph into an autotroph. The species was discovered in January 2012 outside the coast of Nivå, Denmark by professor Øjvind Moestrup.
Triparma is a genus of unicellular algae in the family Triparmaceae in the order Parmales. They form siliceous plates on the cell surface that aid in identification. Triparma is distinguished by its possession of three shield plates, three triradiate girdle plates, a triradiate girdle plate with notched ends, and a small ventral plate. It was first described by Booth & Marchant in 1987 and the holotype is Triparma columacea.
Pyrenomonadaceae is a family of cryptomonads which includes three or four known genera. They are distinguished from other cryptomonads by their nucleomorphs being imbedded into the pyrenoid, and the presence of distinctive pigment phycoerythrin 545.
Chloropicophyceae is a class of green algae in the division Chlorophyta that, along with Picocystophyceae, coincides with the traditional "prasinophyte clade VII".