Golden algae

Golden algae
	Dinobryon divergens, a tree like sessile form with cells in the cup-like shells
Scientific classification
Domain:	Eukaryota
Clade:	Diaphoretickes
Clade:	SAR
Clade:	Stramenopiles
Phylum:	Gyrista
Subphylum:	Ochrophytina
Superclass:	Limnistia
Class:	Chrysophyceae; Pascher, 1914
Orders
	Chromulinales; Chrysosphaerales; Hibberdiales; Hydrurales; Phaeothamniales
Synonyms
	Chrysomonadales Engler 1903; Chrysomonadea Saville-Kent 1881; Chrysomonadina Stein 1878 emend. Klebs 1892;

The Chrysophyceae, usually called chrysophytes, chrysomonads, golden-brown algae or golden algae, are a large group of algae, found mostly in freshwater.^[3] Golden algae is also commonly used to refer to a single species, Prymnesium parvum, which causes fish kills.^[4]

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

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 flagella 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

Stramenopiles

.

Description

The "primary" cell of chrysophytes contains two

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.^[6]

Most members are unicellular flagellates, 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 is sessile and grows in branched colonies. Most forms with silicaceous scales are now considered a separate group, the synurids, but a few belong among the Chromulinales proper, such as Paraphysomonas.
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 slime molds. 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.

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 parenchymatous 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):^[1]^[7]^[8]

Division Chrysophyta
- Class Chrysophyceae
  - Order Chrysomonadales
  - Order Chrysocapsales
  - Order Chrysosphaerales
  - Order Chrysotrichales
- Class
  Heterokontae
- Class Diatomeae

Smith (1938)

According to Smith (1938):

Class Chrysophyceae
- Order Chrysomonadales
  - Suborder Cromulinae (e.g., Mallomonas)
  - Suborder Isochrysidineae (e.g., Synura)
  - Suborder Ochromonadineae (e.g., Dinobryon)
- Order Rhizochrysidales (e.g., Chrysamoeba)
- Order Chrysocapsales (e.g., Hydrurus)
- Order Chrysotrichales (e.g., Phaeothamnion)
- Order Chrysosphaerales (e.g., Epichrysis)

Bourrely (1957)

According to Bourrely (1957):^[9]

Class Chrysophyceae
- Order Phaeoplacales
- Order Stichogloeales
- Order Phaeothamniales
- Order Chrysapionales
- Order Thallochrysidales
- Order Chrysosphaerales
- Order Chrysosaccales
- Order Rhizochrysidales
- Order Ochromonadales
- Order Isochrysidales
- Order Silicoflagellales
- Order Craspedomonadales
- Order Chromulinales

Starmach (1985)

According to Starmach (1985):^[10]

Class Chrysophyceae
- Subclass Heterochrysophycidae
  - Order Chromulinales
  - Order Ochromonadales
- Subclass Acontochrysophycidae
  - Order Chrysarachniales
  - Order Stylococcales
  - Order Chrysosaccales
  - Order Phaeoplacales
- Subclass Craspedomonadophycidae
  - Order Monosigales

Kristiansen (1986)

Classification of the class Chrysophyceae and splinter groups according to Kristiansen (1986):^[10]

Class Chrysophyceae

Class Pedinellophyceae

Order Pedinellales

Class Dictyochophyceae

Order Dictyochales

Margulis et al. (1990)

Classification of the phylum Chrysophyta according to Margulis et al. (1990):^[11]

Phylum Chrysophyta
- Class
  Chrysophyceae
- Class Pedinellophyceae
- Class
  Silicoflagellata
  )

van den Hoek et al. (1995)

According to van den Hoek, Mann and Jahns (1995):

Class Chrysophyceae
- Order Ochromonadales (e.g., Ochromonas, Pseudokephyrion, Dinobryon)
- Order
  Synurophyceae, e.g., Mallomonas, Synura
  )
- Order Pedinellales (= Class Pedinellophyceae, e.g., Pedinella)
- Order Chrysamoebidales (e.g., Rhizochrysis, Chrysarachnion)
- Order Chrysocapsales (e.g., Chrysocapsa, Hydrurus)
- Order Chrysosphaerales (e.g., Chrysosphaera)
- Order Phaeothamniales (e.g., Phaeothamnion, Thallochrysis)

Preisig (1995)

Classification of the class Chrysophyceae and splinter groups according to Preisig (1995):^[10]

Class Chrysophyceae

Order
Bicosoecales
Order Chromulinales
Order Hibberdiales
Order Hydrurales
Order Sancinochrysidales
Order Chrysomioridales

Class Dictyochophyceae

Class
Synurophyceae

Order
Synurales

Guiry and Guiry (2019)

According to Guiry and Guiry (2019):^[12]

Class Chrysophyceae
- Order Chromulinales
- Order Hibberdiales
- Order Hydrurales
- Order Rhizochrysidales
- Order Thallochrysidales
- Chrysophyceae ordo incertae sedis (11 genera)

Ecology

Pond of *hikarimo* ("algae of light") in Hitachi, Japan. Uncertain genus (*Chromulina, Ochromonas* or *Chromophyton*).^[13]^[14]

Chrysophytes live mostly in

oligotrophic freshwater ecosystems, and for assessment of environmental degradation resulting from eutrophication and acid rain.^[15]

Evolution

Fucoxanthin

Chrysophytes contain the pigment fucoxanthin.^[16] Because of this, they were once considered to be a specialized form of cyanobacteria.^{[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.

References

^
S2CID 257830577
.

^ NCBI. Taxonomy Browser (Chrysophyceae)
^ "Introduction to the Chrysophyta". Retrieved 2009-06-13.
^ "Golden Alga: Management Data Series 236: Management of Prymnesium parvum at Texas State Fish Hatcheries".
^ 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.
^ 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.
^
ISBN 9780521462600
.

^ 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. Retrieved 2019-06-03.
^ 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.
^ Goff, Matt. "Chromophyton (Golden Glow Mystery Revisited)". Sitka Nature (online). March 16, 2011. link.
^ Sandgren et al. (1995).
^ "Chrysophyta". Archived from the original on 2008-09-22. Retrieved 2009-06-13.