TheChrysophyceae, usually calledchrysophytes,chrysomonads,golden-brown algae, orgolden algae, are a large group ofalgae, found mostly in freshwater.[3] Golden algae is also commonly used to refer to a single species,Prymnesium parvum, which causesfish kills.[4]
The Chrysophyceae should not be confused with theChrysophyta, which is a more ambiguoustaxon. Although "chrysophytes" is the anglicization of "Chrysophyta", it generally refers to the Chrysophyceae.
Originally they were taken to include all such forms of thediatoms and multicellularbrown algae, but since then they have been divided into several different groups (e.g.,Haptophyceae,[5]Synurophyceae) based on pigmentation and cell structure. Some heterotrophic flagellates as thebicosoecids andchoanoflagellates 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 theflagella 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 polyphyleticChromista. 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 theStramenopiles.
The "primary" cell of chrysophytes contains twospecialized flagella. The active, "feathered" (withmastigonemes) 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. Calledstatospore,stomatocyst orstatocyst, 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.[6]
Most members are unicellularflagellates, with either two visible flagella, as inOchromonas, or sometimes one, as inChromulina. TheChromulinales as first defined by Pascher in 1910 included only the latter type, with the former treated as the orderOchromonadales. 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 asDinobryon, which grows in branched colonies. Most forms with silicaceous scales are now considered a separate group, thesynurids, but a few belong among the Chromulinales proper, such asParaphysomonas.
Some members are generallyamoeboid, with long branching cell extensions, though they pass through flagellate stages as well.Chrysamoeba andRhizochrysis are typical of these. There is also one species,Myxochrysis paradoxa, which has a complex life cycle involving amultinucleate plasmodial stage, similar to those found inslime molds. These were originally treated as the orderChrysamoebales. The superficially similarRhizochromulina was once included here, but is now given its own order based on differences in the structure of the flagellate stage.
Other members are non-motile. Cells may be naked and embedded inmucilage, such asChrysosaccus, or coccoid and surrounded by a cell wall, as inChrysosphaera. A few are filamentous or evenparenchymatous in organization, such asPhaeoplaca. 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 orderHydrurales, but may belong here.
Chrysophytes contain the pigmentfucoxanthin.[16] Because of this, they were once considered to be a specialized form ofcyanobacteria.[citation needed] 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.
^Duff, K. E.; Zeeb, B. A.; Smol, John P. (1995).Atlas of Chrysophycean Cysts. Springer-Science+Business Media, B. V.
^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,[1].
^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.
^Margulis, L., J.O. Corliss, M. Melkonian, D.J. Chapman.Handbook of Protoctista. Jones and Bartlett Publishers, Boston, 1990.
^Guiry, M.D.; Guiry, G.M. (2019)."AlgaeBase". World-wide electronic publication, National University of Ireland, Galway. Retrieved2019-06-03.
^Ohishi H.; Yano H.; Ito H.; Nakahara M. 1991. Observations on a chrysophyte hikarimo in a pond in Hyogo prefecture, Japan. [兵庫県内の池に発生したヒカリモ(黄金藻)の観察.]Japanese Journal of Phycology 39(1): 37-42,link.
Sandgren, C.D., J.P. Smol, and J. Kristiansen [Eds.]. 1995.Chrysophyte algae: ecology, phylogeny and development. Cambridge University Press, New York.ISBN0-521-46260-6.
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
