The Chrysophyceae, usually called chrysophytes, chrysomonads, golden-brown algae, or golden algae, are a large group of algae, found mostly in freshwater.
The Chrysophyceae should not be confused with the Chrysophyta, which is a more ambiguous taxon. Although "chrysophytes" is the anglicization of "Chrysophyta", it generally refers to the Chrysophyceae.
Members
Originally they were taken to include all such forms of the
and multicellular
brown algae, but since then they have been divided into several different groups (e.g.,
Haptophyceae,
[Medlin, L. K., W. H. C. F. Kooistra, D. Potter, G. W. Saunders, and R. A. Anderson. 1997. Phylogenetic relationships of the “golden algae” (haptophytes, heterokont chromophytes) and their plastids. Plant Systematics and Evolution (Supplement) 11: 187–219.] Synurophyceae) based on pigmentation and cell structure. Some heterotrophic flagellates as the
and choanoflagellates were sometimes seen as related to golden algae too.
They are now usually restricted to a core group of closely related forms, distinguished primarily by the structure of the flagellum in motile cells, also treated as an order Chromulinales. It is possible membership will be revised further as more species are studied in detail.
The Chrysophyceae have been placed by some in the polyphyletic Chromista. The broader monophyletic group to which the Chrysophyceae belong includes various non-algae including the bicosoecids, not the collar flagellates, opalines, oomycete fungi, proteromonads, actinophryid heliozoa, and other heterotrophic flagellates and is referred to as the Stramenopiles.
Description
The "primary" cell of chrysophytes contains two
heterokont. The active, "feathered" (with
mastigonemes) flagellum is oriented toward the moving direction. The smooth passive flagellum, oriented toward the opposite direction, may be present only in rudimentary form in some species.
An important characteristic used to identify members of the class Chrysophyceae is the presence of a siliceous cyst that is formed endogenously. Called statospore, stomatocyst or statocyst, this structure is usually globose and contains a single pore. The surface of mature cysts may be ornamented with different structural elements and are useful to distinguish species.
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Most members are unicellular , with either two visible flagella, as in Ochromonas, or sometimes one, as in Chromulina. The Chromulinales as first defined by Pascher in 1910 included only the latter type, with the former treated as the order Ochromonadales. However, structural studies have revealed that a short second flagellum, or at least a second basal body, is always present, so this is no longer considered a valid distinction. Most of these have no cell covering. Some have loricae or shells, such as Dinobryon, which grows in branched colonies. Most forms with silicaceous scales are now considered a separate group, the , but a few belong among the Chromulinales proper, such as Paraphysomonas.
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Some members are generally amoeboid, with long branching cell extensions, though they pass through flagellate stages as well. Chrysamoeba and Rhizochrysis are typical of these. There is also one species, Myxochrysis paradoxa, which has a complex life cycle involving a multinucleate plasmodial stage, similar to those found in . These were originally treated as the order Chrysamoebales. The superficially similar Rhizochromulina was once included here, but is now given its own order based on differences in the structure of the flagellate stage.
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Other members are non-motile. Cells may be naked and embedded in mucilage, such as Chrysosaccus, or coccoid and surrounded by a cell wall, as in Chrysosphaera. A few are filamentous or even in organization, such as Phaeoplaca. These were included in various older orders, most of the members of which are now included in separate groups. Hydrurus and its allies, freshwater genera which form branched gelatinous filaments, are often placed in the separate order Hydrurales, but may belong here.
Classifications
Pascher (1914)
Classification of the class Chrysophyceae according to Pascher (1914):
[Round, F.E. (1986). The Chrysophyta - a reassessment. In: Chrysophytes: Aspects and Problems. Kristiansen, J. and R.A. Andersen Eds.. Cambridge University Press, Cambridge, p. 12.][Sharma, O. P. (1986). Textbook of Algae. McGraw Hill. p. 23, [3].]
Smith (1938)
According to
Smith system:
Bourrely (1957)
According to Bourrely (1957):
[Andersen, R.A. (2007). Molecular systematics of the Chrysophyceae and Synurophyceae. In: Unravelling the algae: the past, present, and future of algal systematics. The Systematics Association Special Volume Series, 75. (Brodie, J. & Lewis, J. Eds), pp. 285-313. Boca Raton: CRC Press.]
Starmach (1985)
According to Starmach (1985):
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Class Chrysophyceae
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Subclass Heterochrysophycidae
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Subclass Acontochrysophycidae
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Subclass Craspedomonadophycidae
Kristiansen (1986)
Classification of the class Chrysophyceae and splinter groups according to Kristiansen (1986):
- * Order Ochromonadales
- * Order Mallomonadales
- * Order Chrysamoebales
- * Order Chrysocapsales
- * Order Hydrurales
- * Order Chrysosphaerales
- * Order Phaeothamniales
- * Order Sarcinochrysidales
- * Order Pedinellales
- * Order Dictyochales
Margulis et al. (1990)
Classification of the phylum Chrysophyta according to Margulis et al. (1990):
[Lynn Margulis, J.O. Corliss, M. Melkonian, D.J. Chapman. Handbook of Protoctista. Jones and Bartlett Publishers, Boston, 1990.]
van den Hoek et al. (1995)
According to van den Hoek, Mann and Jahns (1995):
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Class Chrysophyceae
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Order Ochromonadales (e.g., Ochromonas, Pseudokephyrion, Dinobryon)
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Order Mallomonadales (= Class Synurophyceae, e.g., Mallomonas, Synura)
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Order Pedinellales (= Class Pedinellophyceae, e.g., Pedinella)
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Order Chrysamoebidales (e.g., Rhizochrysis, Chrysarachnion)
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Order Chrysocapsales (e.g., Chrysocapsa, Hydrurus)
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Order Chrysosphaerales (e.g., Chrysosphaera)
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Order Phaeothamniales (e.g., Phaeothamnion, Thallochrysis)
Preisig (1995)
Classification of the class Chrysophyceae and splinter groups according to Preisig (1995):
- * Order Bicosoecales
- * Order Chromulinales
- * Order Hibberdiales
- * Order Hydrurales
- * Order Sancinochrysidales
- * Order Chrysomioridales
- * Order Pedinellales
- * Order Rhizochromulinales
- * Order Dictyochales
- * Order Synurales
Guiry and Guiry (2019)
According to Guiry and Guiry (2019):
Ecology
Chrysophytes live mostly in
freshwater, and are important for studies of
food web dynamics in
oligotrophic freshwater ecosystems, and for assessment of environmental degradation resulting from
eutrophication and
acid rain.
[Sandgren et al. (1995).]
Evolution
Chrysophytes contain the pigment
fucoxanthin.
Because of this, they were once considered to be a specialized form of
cyanobacteria. Because many of these organisms had a silica capsule, they have a relatively complete fossil record, allowing modern biologists to confirm that they are, in fact, not derived from cyanobacteria, but rather an ancestor that did not possess the capability to photosynthesize. Many of the chrysophyta precursor fossils entirely lacked any type of photosynthesis-capable pigment. The most primitive stramenopiles are regarded as heterotrophic, such as the ancestors of the Chrysophyceae were likely heterotrophic flagellates that obtained their ability to photosynthesize from an endosymbiotic relationship with fucoxanthin-containing cyanobacteria.
Bibliography
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Andersen, R. A. 2004. Biology and systematics of heterokont and haptophyte algae. American Journal of Botany 91(10): 1508–1522. 2004.
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Duff, K.E., B.A. Zeeb & J.P. Smol. 1995. Atlas of Chrysophycean Cysts, Vol. 1., [6]; 2001, Vol. 2, [7]. Kluwer Academic Publishers, Dordrecht.
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Jørgen Kristiansen. 2005. Golden algae: a biology of chrysophytes. A.R.G. Gantner Verlag, distributed by Koeltz Scientific Books, Königstein, Germany, vii + 167 pp. .
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Kristiansen, J. and R.A. Andersen Eds.. 1986. Chrysophytes: Aspects and Problems. Cambridge University Press, Cambridge, xiv + 337 pp.
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Kristiansen, J. and Preisig, H. Eds.. 2001. Encyclopedia of chrysophyte genera. Bibliotheca Phycologica, Vol. 110, J. Cramer, Berlin.
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Medlin, L. K., W. H. C. F. Kooistra, D. Potter, G. W. Saunders, and R. A. Anderson. 1997. Phylogenetic relationships of the “golden algae” (haptophytes, heterokont chromophytes) and their plastids. Plant Systematics and Evolution (Supplement) 11: 187–219.
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Sandgren, C.D., J.P. Smol, and J. Kristiansen Eds.. 1995. Chrysophyte algae: ecology, phylogeny and development. Cambridge University Press, New York. .
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Škaloud, P., Škaloudová, M., Pichrtová, M., Němcová, Y., Kreidlová, J. & Pusztai, M. 2013. www.chrysophytes.eu – a database on distribution and ecology of silica-scaled chrysophytes in Europe. Nova Hedwigia, Beiheft 142: 141-146. link
