Labyrinthulomycetes (

ICNafp The ''International Code of Nomenclature for algae, fungi, and plants'' (ICN or ICNafp) is the set of rules and recommendations dealing with the formal botanical names that are given to plants, fungi and a few other groups of organisms, all th ...

) or Labyrinthulea (

ICZN The International Code of Zoological Nomenclature (ICZN) is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals. It is also informally known as the ICZN Code, for its formal author, t ...

) is a

class Class, Classes, or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used d ...

protist A protist ( ) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus. Protists do not form a natural group, or clade, but are a paraphyletic grouping of all descendants of the last eukaryotic common ancest ...

s that produce a network of filaments or tubes, which serve as tracks for the cells to glide along and absorb

nutrients A nutrient is a substance used by an organism to survive, grow and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...

for them. The two main groups are the labyrinthulids (or slime nets) and thraustochytrids. They are mostly marine, commonly found as

parasite Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted str ...

s on

alga Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular microalgae, suc ...

e and

seagrass Seagrasses are the only flowering plants which grow in marine (ocean), marine environments. There are about 60 species of fully marine seagrasses which belong to four Family (biology), families (Posidoniaceae, Zosteraceae, Hydrocharitaceae and ...

es or as decomposers on dead plant material. They also include some parasites of marine invertebrates and

mixotroph A mixotroph is an organism that uses a mix of different sources of energy and carbon, instead of having a single trophic mode, on the continuum from complete autotrophy to complete heterotrophy. It is estimated that mixotrophs comprise more than ...

ic 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 A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. Bi ...

. 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 In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid) is a solid that lacks the long-range order that is a characteristic of a crystal. The terms "glass" and "glassy solid" are sometimes used synonymousl ...

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 A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...

, but a

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

group of

eukaryote The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...

s within the

Stramenopiles The stramenopiles, also called heterokonts, are Protist, protists distinguished by the presence of stiff tripartite external hairs. In most species, the hairs are attached to flagella, in some they are attached to other areas of the cellular sur ...

. They belong to the phylum

Bigyra Bigyra () is a phylum of microscopic eukaryotes that are found at the base of the Stramenopiles clade. It includes three well-known heterotrophic groups Bicosoecida, Opalinata and Labyrinthulomycetes, as well as several small clades initially disc ...

, which contains other heterotrophic microorganisms such as the

bicosoecid Bicosoecida ( ICZN) or Bicosoecales/Bicoecea ( ICBN) is an order of Bikosea, a small group of unicellular flagellates, included among the stramenopiles. Informally known as bicosoecids, they are free-living cells, with no chloroplasts, and in som ...

s. Considering that the

plastid A plastid is a membrane-bound organelle found in the Cell (biology), cells of plants, algae, and some other eukaryotic organisms. Plastids are considered to be intracellular endosymbiotic cyanobacteria. Examples of plastids include chloroplasts ...

s from

are possibly the result of an event of

endosymbiosis An endosymbiont or endobiont is an organism that lives within the body or cells of another organism. Typically the two organisms are in a mutualism (biology), mutualistic relationship. Examples are nitrogen-fixing bacteria (called rhizobia), whi ...

in their

last common ancestor A most recent common ancestor (MRCA), also known as a last common ancestor (LCA), is the most recent individual from which all organisms of a set are inferred to have descended. The most recent common ancestor of a higher taxon is generally assu ...

, the bicosoecids and the labyrinthulomycetes could have originated from a

mixotrophic A mixotroph is an organism that uses a mix of different sources of energy and carbon, instead of having a single trophic mode, on the continuum from complete autotrophy to complete heterotrophy. It is estimated that mixotrophs comprise more than ...

algal Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular microalgae, s ...

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

chloroplast A chloroplast () is a type of membrane-bound organelle, organelle known as a plastid that conducts photosynthesis mostly in plant cell, plant and algae, algal cells. Chloroplasts have a high concentration of chlorophyll pigments which captur ...

s. 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

, the labyrinthulomycetes are the

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

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 In biology, a phylum (; : phyla) is a level of classification, or taxonomic rank, that is below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botany the term division (taxonomy), division has been used instead ...

Labyrinthulomycota. They were originally considered unusual

slime mould Slime mold or slime mould is an informal name given to a polyphyletic assemblage of unrelated eukaryotic organisms in the Stramenopiles, Rhizaria, Discoba, Amoebozoa and Holomycota clades. Most are near-microscopic; those in the Myxogastria ...

s, 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

heterokont The stramenopiles, also called heterokonts, are protists distinguished by the presence of stiff tripartite external hairs. In most species, the hairs are attached to flagella, in some they are attached to other areas of the cellular surface, an ...

s, 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 ** Family Aplanochytriaceae/ Aplanochytriidae *** '' Aplanochytrium'' ''Labyrinthuloides'' ">Labyrinthuloides.html" ;"title="''Labyrinthuloides">''Labyrinthuloides'' ** Family Labyrinthulaceae/Labyrinthulidae *** ''Labyrinthomyxa'' *** ''Pseudoplasmodium'' *** '' Labyrinthula'' [=''Labyrinthodictyon'' ; ''Labyrinthorhiza'' ] ** 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'' * Order Oblongichytriales/ Oblongichytrida ** Family Oblongichytriaceae/ Oblongichytriidae *** '' Oblongichytrium'' * Order Thraustochytriales/ Thraustochytrida ** '' Pyrrhosorus'' Juel 1901 ** '' Thanatostrea'' Franc & Arvy 1969 ** Family Althornidiaceae/ Althorniidae *** '' Althornia'' ** Family Thraustochytriacae/ Thraustochytriidae *** '' 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 ** Family "Amphitremidiaceae"/ Amphitremidae *** '' Paramphitrema'' *** '' Archerella'' *** '' Amphitrema'' ** Family "Diplophrydaceae"/ Diplophryidae *** '' Diplophrys'' * Order "Amphifilales"/ Amphifilida ** 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 A mitochondrion () is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is us ...

which use as a

stop codon In molecular biology, a stop codon (or termination codon) is a codon (nucleotide triplet within messenger RNA) that signals the termination of the translation process of the current protein. Most codons in messenger RNA correspond to the additio ...

instead of coding for

Leucine Leucine (symbol Leu or L) is an essential amino acid that is used in the biosynthesis of proteins. Leucine is an α-amino acid, meaning it contains an α-amino group (which is in the protonated −NH3+ form under biological conditions), an α-Car ...

. This code is represented by

NCBI The National Center for Biotechnology Information (NCBI) is part of the National Library of Medicine (NLM), a branch of the National Institutes of Health (NIH). It is approved and funded by the government of the United States. The NCBI is loca ...

translation table 23, ''Thraustochytrium'' mitochondrial code.

Gallery

File:Aplanolm.jpg, '' Aplanochytrium'' sp. under

light microscope The optical microscope, also referred to as a light microscope, is a type of microscope that commonly uses visible spectrum, visible light and a system of lens (optics), lenses to generate magnified images of small objects. Optical microscopes ...

File:Aplanosem.png, ''Aplanochytrium'' sp. under SEM File:Aurantiochytrium limacinum SR21.jpg, ''Aurantiochytrium'' sp. File:Collection Penard MHNG Specimen 48-2-4 Amphitrema stenostoma.tif, Test of '' Amphitrema'', a testate amoeba recently included in the group File:Tsenkovsky Lev Semyonovich.jpg, Leon Cienkowski, Russian botanist who in 1867 described '' Labyrinthula'', the first genus of the groupCienkowski, L. (1867). Ueber den Bau und die Entwicklung der Labyrinthuleen. ''Arch. mikr. Anat.'', 3:274

References

External links

Labyrinthulomycota
{{Taxonbar, from1=Q1148791, from2=Q16653009, from3=Q131275915 Stramenopile classes Bigyra