• Source: Labyrinthulomycetes

Labyrinthulomycetes (ICBN) or Labyrinthulea (ICZN) is a class of protists that produce a network of filaments or tubes, which serve as tracks for the cells to glide along and absorb nutrients for them. The two main groups are the labyrinthulids (or slime nets) and thraustochytrids. They are mostly marine, commonly found as parasites on algae and seagrasses or as decomposers on dead plant material. They also include some parasites of marine invertebrates and mixotrophic species that live in a symbiotic relationship with zoochlorella.




Characteristics



Although they are outside the cells, the filaments of Labyrinthulomycetes are surrounded by a membrane. They are formed and connected with the cytoplasm by a unique organelle called a sagenogen or bothrosome. The cells are uninucleated and typically ovoid, and move back and forth along the amorphous network at speeds varying from 5-150 μm per minute. Among the labyrinthulids, the cells are enclosed within the tubes, and among the thraustochytrids, they are attached to their sides.




Evolution






= Evolutionary origin

=
Labyrinthulomycetes are not fungi, but a monophyletic group of eukaryotes within the Stramenopiles. They belong to the phylum Bigyra, which contains other heterotrophic microorganisms such as the bicosoecids. Considering that the plastids from Stramenopiles are possibly the result of an event of endosymbiosis in their last common ancestor, the bicosoecids and the labyrinthulomycetes could have originated from a mixotrophic algal common ancestor that secondarily lost their plastids.
Some characteristics of the labyrinthulomycetes can be explained by their origin from ancestral plastids. They produce omega-3 poly-unsaturated fatty acids using a desaturase usually present in chloroplasts. The zoospores of labyrinthulids have an eyespot composed of membrane-bound granules that resembles eyespots of photosynthetic stramenopiles, which are either within a plastid or believed to be derived from a plastid.
Within Bigyra, the labyrinthulomycetes are the sister group to Eogyrea, a class containing the species Pseudophyllomitus vesiculosus and the environmental clade called MAST-4. Together they compose the subphylum Sagenista.




Classification


Labyrinthulomycetes or Labyrinthulea used to compose the defunct fungal phylum Labyrinthulomycota. They were originally considered unusual slime moulds, although they are not very similar to the other sorts. The structure of their zoospores and genetic studies show them to be a primitive group of heterokonts, but their classification and treatment remains somewhat unsettled.
This class usually contained two orders, Labyrinthulales and Thraustochytriales (ICBN), or Labyrinthulida and Thraustochytrida (ICZN), but a different classification has recently been proposed.

Order Labyrinthulales/Labyrinthulida E. A. Bessey 1950/Doffein 1901
Family Aplanochytriaceae/Aplanochytriidae Leander ex Cavalier-Smith 2012
Aplanochytrium Bahnweg & Sparrow 1972 [=Labyrinthuloides Perkins 1973]
Family Labyrinthulaceae/Labyrinthulidae Haeckel 1868/Cinekowksa 1867
Labyrinthomyxa Duboscq 1921
Pseudoplasmodium Molisch 1925
Labyrinthula Cienkowski 1864 [=Labyrinthodictyon Valkanov 1969; Labyrinthorhiza Chadefaud 1956]
Family-level clade "Stellarchytriaceae/Stellarchytriidae" – this group is provisionally placed in Labyrinthulida but, according to phylogenetic analyses, diverges before the rest of labyrinthulean clades.
Stellarchytrium FioRito & Leander 2016
Order Oblongichytriales/Oblongichytrida
Family Oblongichytriaceae/Oblongichytriidae Cavalier-Smith 2012
Oblongichytrium Yokoyama & Honda 2007
Order Thraustochytriales/Thraustochytrida Sparrow 1973
Pyrrhosorus Juel 1901
Thanatostrea Franc & Arvy 1969
Family Althornidiaceae/Althorniidae Jones & Alderman 1972
Althornia Jones & Alderman 1972
Family Thraustochytriacae/Thraustochytriidae Sparrow ex Cejp 1959
Japanochytrium Kobayasi & Ôkubo 1953
Monorhizochytrium Doi & Honda 2017
Sicyoidochytrium Yokoy., Salleh & Honda 2007
Aurantiochytrium Yokoy. & Honda 2007
Ulkenia Gaertn. 1977
Parietichytrium Yokoy., Salleh & Honda 2007
Botryochytrium Yokoy., Salleh & Honda 2007
Schizochytrium Goldst. & Belsky emend. Booth & Mill.
Thraustochytrium Sparrow 1936
Hondaea Amato & Cagnac 2018
Labyrinthulochytrium Hassett & Gradinger 2018
Order "Amphitremidales"/Amphitremida Gomaa et al. 2013
Family "Amphitremidiaceae"/Amphitremidae Poch 1913
Paramphitrema Valkanov 1970
Archerella Loeblich & Tappan 1961
Amphitrema Archer 1867
Family "Diplophrydaceae"/Diplophryidae Cavalier-Smith 2012
Diplophrys Barker 1868
Order "Amphifilales"/Amphifilida Cavalier Smith 2012
Family Sorodiplophryidae Cavalier-Smith 2012
Sorodiplophrys Olive & Dykstra 1975
Fibrophrys Takahashi et al. 2016
Family Amphifilidae Cavalier-Smith 2012
Genus Amphifila Cavalier-Smith 2012




Genetic code


The labyrinthulomycete Thraustochytrium aureum is notable for the alternative genetic code of its mitochondria which use TTA as a stop codon instead of coding for Leucine. This code is represented by NCBI translation table 23, Thraustochytrium mitochondrial code.




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References






External links



Labyrinthulomycota

Kata Kunci Pencarian:

• Protista
• Jamur lendir
• Opisthokonta
• Heterokonta
• Labyrinthulomycetes
• Slime mold
• Gorgonia ventalina
• Marine snow
• Bigyra
• Opisthokont
• Thraustochytriidae
• Flagellate
• Protist
• Thraustochytrids