Heterokontophyta

Heterokonts

Pacific rockweed, Fucus distichus, in Olympic National Park
Scientific classification
Domain:Eukaryota
Kingdom:Chromalveolata
Phylum:Heterokontophyta
Typical classes


Colored groups
Chrysophyceae (golden algae)
Synurophyceae
Actinochrysophyceae (axodines)
Pelagophyceae
Phaeothamniophyceae
Bacillariophyceae (diatoms)
Bolidophyceae
Raphidophyceae
Eustigmatophyceae
Xanthophyceae (yellow-green algae)
Phaeophyceae (brown algae)
Colorless groups
Oomycetes (water moulds)
Hyphochytridiomycetes
Bicosoecea
Labyrinthulomycetes (slime nets)
Opalinea
Proteromonadea


The heterokonts or stramenopiles are a major line of eukaryotes presently containing about 10,500 known species.[1] Most are algae, ranging from the giant multicellular kelp to the unicellular diatoms, which are a primary component of plankton. Other notable members of the Stramenopila include the (generally parasitic) oomycetes, including Phytophthora of Irish potato famine fame and Pythium which causes seed rot and damping off.

Chloroplasts

Heterokont algae are chromists with chloroplasts surrounded by four membranes, which are counted from the outermost to the innermost membrane. The first membrane is continuous with the host's chloroplast endoplasmic reticulum, or cER. The second membrane presents a barrier between the lumen of the endoplasmic reticulum and the primary endosymbiont or chloroplast, which represents the next two membranes, within which the thylakoid membranes are found. This arrangement of membranes suggest that heterokont chloroplasts were obtained from the reduction of a symbiotic red algal eukaryote, which had arisen by evolutionary divergence from the monophyletic primary endosymbiotic ancestor that is thought to have given rise to all eukaryotic photoautotrophs. The chloroplasts characteristically contain chlorophyll a and chlorophyll c, and usually the accessory pigment fucoxanthin, giving them a golden-brown or brownish-green color.

Most basal heterokonts are colorless, suggesting they diverged before aqcuisition of chloroplasts within the group. However, fucoxanthin-containing chloroplasts are also found among the haptophytes, and evidence suggests that the two groups have a common ancestry, as well as possible a common phylogenetic history with cryptomonads. In this case the ancestral heterokont was an alga, and all colorless groups arose through loss of the secondary endosymbiont and hence its chloroplast.

Motile cells

Many heterokonts are unicellular flagellates, and most others produce flagellate cells at some point in their life-cycle, for instance as gametes or zoospores. The name heterokont refers to the characteristic form of these cells, which typically have two unequal flagella. The anterior or tinsel flagellum is covered with lateral bristles or mastigonemes, while the other flagellum is whiplash, smooth and usually shorter, or sometimes reduced to a basal body. The flagella are inserted subapically or laterally, and are usually supported by four microtubule roots in a distinctive pattern.

Mastigonemes are manufactured from glycoproteins in the cell's endoplasmic reticulum before being transported to its surface. When the tinsel flagellum moves, these create a backwards current, pulling the cell through the water or bringing in food. The mastigonemes have a peculiar tripartite structure, which may be taken as the defining characteristic of the group, thereby including a few protists that do not produce cells with the typical heterokont form. They have been lost in a few lines, most notably the diatoms.

Classification

As noted above, classification varies considerably. Originally the heterokont algae were treated as two divisions, first within the kingdom Plantae and later the Protista:

Division Chrysophyta
    Class Chrysophyceae (golden algae)
    Class Bacillariophyceae (diatoms)
Division Phaeophyta (brown algae)

In this scheme, however, the Chrysophyceae are paraphyletic to both other groups. As a result, various members have been given their own classes and often divisions. Recent systems often treat these as classes within a single division, called the Heterokontophyta, Chromophyta or Ochrophyta. This is not universal, however - for instance Round et al. treat the diatoms as a division.

The discovery that oomycetes and hypochytrids are related to these algae, rather than fungi as previously thought, has led many authors to include them among the heterokonts. Should it turn out that they evolved from colored ancestors, the group would be paraphyletic in their absence. Once again, however, usage varies. David J. Patterson named this extended group the stramenopiles, characterized by the presence of tripartite mastigonemes, mitochondria with tubular cristae, and open mitosis. He used the stramenopiles as a prototype for a classification without Linnaean ranks. Their composition has been essentially stable, but their use within ranked systems varies.

The origin of the name stramenopile is explained by Adl and coauthors:

Regarding the spelling of stramenopile, it was originally spelled stramenopile. The Latin word for ‘‘straw’’ is stramine-us, -a, -um, adj. [stramen], made of straw—thus, it should have been spelled straminopile. However, Patterson (1989)[1] clearly stated that this is a common name (hence, lower case, not capitalized) and as a common name, it can be spelled as Patterson chooses. If he had stipulated that the name was a formal name, governed by rules of nomenclature, then his spelling would have been an orthogonal mutation and one would simply correct the spelling in subsequent publications (e.g. Straminopiles). But, it was not Patterson’s desire to use the term in a formal sense. Thus, if we use it in a formal sense, it must be formally described (and in addition, in Latin, if it is to be used botanically). However, and here is the strange part of this, many people liked the name, but wanted it to be used formally. So they capitalized the first letter, and made it Stramenopiles; others corrected the Latin spelling to Straminopiles.[2]


Thomas Cavalier-Smith treats the heterokonts as identical in composition with the stramenopiles; this is the definition followed here. He has proposed placing them in a separate kingdom Chromalveolata, together with the haptophytes, cryptomonads and alveolates. This is one of the most common revisions to the five-kingdom system, but has not been generally adopted, partly because some biologists doubt their monophyly. A few treat the Chromalveolata as identical in composition with the heterokonts, or list them as a kingdom Stramenopila.

References

1. ^ Patterson, D. J. (1999). The diversity of eukaryotes. American Naturalist 154: S96-S124
2. ^ Adl, S. M. et al. (2005). "The new higher level classification of eukaryotes with emphasis on the taxonomy of protists. Journal of Eukaryotic Microbiology 52: 399-451.

Further reading

  • Fletcher, R.L.1987. Seaweeds of the British Isles. Volume 3 Fucophyceae (Phaeophyceae) Part 1. British Museum (Natural History, London. ISBN 0 565 00992 3

External links

Location Washington, USA
Nearest city Port Angeles
Coordinates
Area 922,561 acres (3,734 km²)
Established June 29, 1938
Total visitation 2,749,197 (in 2006)
Governing body
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Scientific classification or biological classification is a method by which biologists group and categorize species of organisms. Scientific classification also can be called scientific taxonomy, but should be distinguished from folk taxonomy, which lacks scientific basis.
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Chromalveolata
Cavalier-Smith, 1998

Phyla
Heterokontophyta
Haptophyta
Cryptophyta
Alveolata
  • Ciliophora
  • Apicomplexa
  • Dinoflagellata


Chromalveolata
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Chrysophyceae

The golden algae or chrysophytes are a large group of heterokont algae, found mostly in freshwater. Originally they were taken to include all such forms except the diatoms and multicellular brown algae, but since then they have been divided into
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Synurophyceae

The synurids are a small group of heterokont algae, found mostly in freshwater, which are covered in silicate scales and spines. These are formed on the surface of the chloroplasts, of which there are usually two, but sometimes only one divided
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Actinochrysophyceae

Genera

Silicoflagellates
   Dictyocha
   Rhizochromulina
Actinodines
   Pedinella
   Apedinella
   
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Pelagophyta

Pelagophytes are a type of heterokont algae.
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Bacillariophyceae

Orders
  • Centrales
  • Pennales
Diatoms (Greek: διά (dia) = "through" + τέμνειν
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Raphidophyceae

Raphidophytes are a small group of eukaryotic algae that includes both marine and freshwater species[1]. All raphidophytes are unicellular, with large cells (50 → 100 μm) but no cell walls.
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Eustigmatophyceae

Eustigmatophytes are a small group (7 genera; ~12 species) of eukaryotic algae that includes marine, freshwater and soil-living species[1]. All eustigmatophytes are unicellular, with coccoid cells and polysaccharide cell walls.
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Xanthophyceae
Allorge ex Fritsch

Yellow-green algae or xanthophytes are an important group of heterokont algae. Most live in freshwater, but some are found in marine and soil habitats.
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Phaeophyceae
Kjellman

The Phaeophyceae or brown algae, (singular: alga) is a large group of mostly marine multicellular algae, including many seaweeds of colder Northern Hemisphere waters.
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Oomycetes

Orders

Lagenidiales
Leptomitales
Peronosporales
Rhipidiales
Saprolegniales
Sclerosporales
Water molds (or water moulds: see spelling differences) also known as Oomycetes
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Hyphochytridiomycetes

Constituent Order

Hyphochytriales

Hyphochytridiomycota is a phylum of "fungi" (actually classified as protists), within the Kingdom Chromalveolata.
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Bicosoecea

Genera
Bicosoeca
Cafeteria
Pseudobodo
Siluania
Symbiomonas
The biocosoecids are a small group of unicellular flagellates, included among the heterokonts.
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Labyrinthulomycetes

Genera

Labyrinthulids
Labyrinthula
Thraustochytrids
Aplanochytrium
Labyrinthuloides
Japonochytrium
Schizochytrium
Thraustochytrium
Ulkenia
Diplophryids
Diplophrys
The Labyrinthulomycetes
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Opalinea

Genera

Opalina
Protoopalina
Zelleriella
Protozelleriella
Cepedea
The opalines are a small group of peculiar protists, found as endosymbionts in the gut of frogs and toads.
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phytoplankton — provide the food base for most marine food chains. In very high densities (so-called algal blooms) these algae may discolor the water and outcompete or poison other life forms.
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Laminariales
Migula

Families

Alariaceae
Chordaceae
Laminariaceae
Lessoniaceae
Phyllariaceae
Pseudochordaceae

Kelp are large seaweeds (algae), belonging to the brown algae and classified in the order Laminariales.
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Bacillariophyceae

Orders
  • Centrales
  • Pennales
Diatoms (Greek: διά (dia) = "through" + τέμνειν
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Plankton are any drifting organism that inhabits the pelagic zone of oceans, seas, or bodies of fresh water. It is a description of life-style rather than a genetic classification.
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Parasitism is one version of symbiosis ("living together"), a phenomenon in which two organisms which are phylogenetically unrelated co-exist over a prolonged period of time, usually the lifetime of one of the individuals.
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Oomycetes

Orders

Lagenidiales
Leptomitales
Peronosporales
Rhipidiales
Saprolegniales
Sclerosporales
Water molds (or water moulds: see spelling differences) also known as Oomycetes
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Phytophthora

Species
Phytophthora arecae
Phytophthora botryosa
Phytophthora cactorum
Phytophthora cajani
Phytophthora cambivora
Phytophthora capsici
Phytophthora cinnamomi
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Pythium

Species

Pythium acanthicum
Pythium acanthophoron
Pythium acrogynum
Pythium adhaerens
Pythium amasculinum
Pythium anandrum
Pythium angustatum

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The Chromista are a paraphyletic eukaryotic supergroup, which may be treated as a separate kingdom or included among the Protista. They include all algae whose chloroplasts contain chlorophylls a and c
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Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. Chloroplasts absorb sunlight and use it in conjunction with water and carbon dioxide to produce sugars, the raw material for energy and biomass production in all green plants
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