Golden Algae

The algae group of Chrysophyceae is generally also known as chrysomonads or chrysophytes, and algae that belong to this group is called Golden Algae. Golden algae, commonly found in freshwater habitats, are sometimes also known as golden-brown algae, and they are closely associated with the brown algae group. Golden algae, which belongs to the phylum 'Ochrophyta', was often considered as the member species of the brown algae group. Group division or species classification of golden algae is mostly confusing, and they are also classified into the Chrysophyta phylum (which is an algal phylum that also includes yellow-green algae or xanthophytes). Golden algae are also characterized by their flagellar structure, which is one of their general characteristics. This article talks about the description of golden algae and answers many questions related to them, such as questions related to their habitats, why they are known as golden algae or golden-brown algae, and many more.

Golden Algae

The Chrysophycea, which are the common components of the plankton groups found in oligotrophic lakes, is commonly known as Golden Algae or sometimes, they are even called Golden-Brown Algae. Golden algae, also called the chrysophytes, are algal species mostly found in freshwater habitats. Sometimes, golden algae term is also used to refer to a single species of algae, i.e., Prymnesium parvum (An algae species that cause fish kills in the freshwater habitat). Dinobryon divergens, a golden algae species, generally form a tree-like sessile structure or form with its cells present in the cup-like shells that give them this form. The Chrysophyceae (a golden algae group) should not be confused with a more ambiguous taxon group of algae, i.e., Chrysophyta. However, it is considered that the chrysophytes are the anglicization of the Chrysophyta group, but generally, the chrysophytes term refers to the golden algae (Chrysophyceae).

Following are the common synonyms or similar terms which are used to refer to the golden algae group:

Chrysomonadina, termed by Stein in 1878 and further in 1892 by Klebs,
Chrysomonadea, a term for golden algae, is used by Saville-Kent in 1881,
And last, Chrysomonadales, first termed by Engler in 1903 for golden algae species.

Golden Algae: Etymology

The scientific name for golden algae, chrysophyte, is taken from the ancient Greek language in which 'khrusós' stands for 'gold', and 'phyte' means 'plant.' Thus, together they refer to Golden Algae species.

Golden Algae: Classification and distribution

An algal phylum named Chrysophyta is the phylum for the golden algae species, and this phylum also includes the species generally referred to as 'Yellow-Green Algae.' To be more precise about the classification of golden algae, members of their group belong to the Chrysophyceae subgroup of the Chrysophyta phylum. According to Pascher's system of classification, Chrysophytes or golden algae species are members of class Chrysophyceae, which, together with xenophytes species (yellow-green algae), comprises the phylum Chrysophyta. Following are the orders of the phylum Chrysophyta which comes under the classification of golden algae, and all the members of golden algae species found under these orders only:

Phaeothamniales order
Hibberdiales order
Chromulinales order
Hydrurales order
Chrysosphaerales order

All these orders of the phylum Chrysophyta belong to the members of golden algae, and members of all these orders share some common general characteristics.

Classifications of Golden Algae

The classification of golden algae is not very simple, and it is often very confusing because many persons attempted to classify these species and classified them differently. Therefore, with every new classification of golden algae, it becomes even more confusing to understand the similarity between the members of a group of golden algae. However, still, all these classifications are very much important to study. Therefore, all the classifications of golden algae that have been attempted previously by many botanists have been mentioned in this section. Following is the list of detailed classifications of the golden algae that are classified according to many famous botanists in the past:

1. Classification of golden algae according to Pascher:

Pascher made a classification of golden algae species in the year 1914, and according to this classification, the golden algae species belong to division Chrysophyta, and further, this division Chrysophyta have three following classes: class Chrysophyceae, class Diatomeae and class Heterokontae. Furthermore, the class Chrysophyceae includes the following order of golden algae species according to the Pascher classification:

Chrysomonadales order
Chrysotrichales order
Chrysocapsales order
Chrysosphaerales order

This is complete details about the classification of golden algae according to Pascher.

2. Classification of golden algae according to Smith:

Smith was a famous botanist who classified the golden algae group members in 1938 (more than 2 decades after Pascher's classification). He classified Golden algae in Class Chrysophyceae, and this class consists of the following order of Golden algae species:

Chrysosphaerales order (Example: Epichrysis)
Chrysocapsales order (Example: Hydrurus)
Chrysotrichales order (Example: Phaeothamnion)
Rhizochrysidales order (Example: Chrysamoeba)
Chrysomonadales order

Among the order for golden algae given above, the Chrysomonadales order is further classified into the following suborders by Smith:

Ochromonadineae suborder, which contains Dinobryon and many more such species of golden algae
Cromulinae suborder (Example: Mallomonas)
Isochrysidineae suborder (Example: Synura)

This is complete details of Smith classification of golden algae group where the example of golden algae in each classified order and suborder is provided.

3. Classification of golden algae according to Bourrely:

After Smith, Bourrely was the person who attempted to classify the golden algae species group, and he did the same in 1957, which was also two decades later the Smith classification of golden algae. In the Bourrely classification of golden algae, all golden algae species are included in the class Chrysophyceae. Further according to this classification system, the class Chrysophyceae consists of the following thirteen orders which belong to golden algae species:

Chromulinales order
Silicoflagellales order
Ochromonadales order
Chrysosaccales order
Thallochrysidales order
Phaeothamniales order
Phaeoplacales order
Craspedomonadales order
Isochrysidales order
Rhizochrysidales order
Chrysosphaerales order
Chrysapionales order
Stichogloeales order

4. Classification of golden algae according to Starmach:

Starmach was the next person who introduced a new pattern or system of classification for species belonging to the golden algae group. Starmach introduced his classification system for golden algae in the year 1985, and this was more than 3 decades after Bourrely introduced the classification system. Starmach also made several changes in his classification system for golden algae, and thus his classification system was different from all the other classification systems for golden algae introduced in the past. Starmach, in his classification system for golden algae, introduced that all golden algae species belong to Class Chrysophycea, which further have the following three subclasses:

Craspedomonadophycidae subclass
Acontochrysophycidae subclass
Heterochrysophycidae subclass

Now, each of the subclasses of the Class Chrysophycea contains one or more orders for golden algae species in them, according to the Starmach classification system.

(i) The subclass Heterochrysophycidae contains the following orders of golden algae:

Chromulinales order
Ochromonadales order

(ii) The subclass Craspedomonadophycidae contains the following order of golden algae:

Monosigales order

(iii) The subclass Heterochrysophycidae contains the following orders of golden algae:

Phaeoplacales order
Stylococcales order
Chrysosaccales order
Chrysarachniales order

The above is the complete details about the classification of golden algae according to Starmach.

5. Classification of golden algae according to Kristiansen:

The very next year of which Starmach introduced the classification system for golden algae, Kristiansen was the next person who introduced a new classification system for golden algae in 1986. The classification system for golden algae introduced by Kristiansen was very much different from all who introduced the classification system for golden algae in the past. According to the Kristiansen system of classification for golden algae, golden algae was classified not just into a single class but into three different classes, which are given below:

Pedinellophyceae class
Dictyochophyceae class
Chrysophyceae class

Each Class mentioned above contains one or more orders for golden algae species in them, according to the Kristiansen classification system.

(i) The class Dictyochophyceae contains the following order of golden algae:

Dictyochales order

(ii) The class Pedinellophyceae contains the following order of golden algae:

Pedinellales order

(iii) The class Chrysophyceae contains the following orders of golden algae:

Sarcinochrysidales order
Chrysosphaerales order
Chrysocapsales order
Mallomonadales order
Phaeothamniales order
Hydrurales order
Chrysamoebales order
Ochromonadales order

This is complete details about the classification of golden algae according to Kristiansen.

6. Classification of golden algae according to Margulis et al:

Margulis et al. was the next person after Kristiansen, who introduced a new classification system for golden algae species. Margulis et al. introduced the new classification system for the golden algae group in 1990 in which Margulis classified the golden algae species into the following three classes under phylum Chrysophyta:

Dictyochophyceae class (which is the same as class Silicoflagellata)
Pedinellophyceae class
Chrysophyceae class

This is complete details about the classification of golden algae made according to Margulis et al.

7. Classification of golden algae according to van den Hoek et al:

After the classification system of Margulis et al., Van den Hoek introduced a new classification system for golden algae in 1995, in collaboration with Mann and Jahns. The classification system of Van den Hoek, Mann, and Janas followed a similar classical pattern of classification for golden algae in which they classified golden algae species under Chrysophyceae class. Further, according to their system of classification, class Chrysophyceae have the following orders for golden algae species:

Phaeothamniales order (Example: Thallochrysis, Phaeothamnion, and many more)
Chrysocapsales order (Example: Hydrurus, Chrysocapsa, and many more)
Pedinellales order which is the same as Pedinellophyceae class in other classification systems of golden algae (Example: Pedinella)
Ochromonadales order (Example: Dinobryon, Pseudokephyrion, Ochromonas, and many more)
Chrysosphaerales order (Example: Chrysosphaera)
Chrysamoebidales order (Example: Chrysarachnion, Rhizochrysis, and many more)
Mallomonadales order which is the same as Synurophyceae class in other classification systems of golden algae (Example: Synura, Mallomonas, and many more)

This is complete details of Van den Hoek, Janas, and Mann's classification system of golden algae group where the example of golden algae species for each classified order is provided with them.

8. Classification of golden algae according to Preisig classification system:

In the same year, when Van den Hoek, Janas, and Mann introduced their system of classification for golden algae species (which is 2015), Preisig was the person who also introduced a separate system of classification for the golden algae group. But Preisig published his classification system for the golden algae group after the publication of Van den Hoek, Janas, and Mann classification system. In his classification system, Preisig classified the golden algae group into the following three classes:

Synurophyceae class
Dictyochophyceae class
Chrysophyceae class

Each Class mentioned above contains one or more orders for golden algae species in them, according to the Preisig classification system.

(i) The class Dictyochophyceae contains the following order of golden algae:

Dictyochales order
Pedinellales order
Rhizochromulinales order

(ii) The class Synurophyceae contains the following order of golden algae:

Synurales order

(iii) The class Chrysophyceae contains the following orders of golden algae:

Chrysomeridales order
Hydrurales order
Chromulinales order
Sancinochrysidales order
Hibberdiales order
Bicosoecales order

This is complete details about the classification of golden algae made according to Preisig.

9. Classification of golden algae group according to Guiry and Guiry:

The last ones in this list who introduced a new classification system for the golden algae group were Guiry and Guiry, and they introduced their new classification system recently and more than two decades after the publication of Preisig's classification system, i.e., in the year 2019. According to the classification system of Guiry and Guiry for the golden algae group, species belonging to this group are classified into one class (which is even seen in almost all classification systems introduced before), i.e., Class Chrysophyceae. Further, this class Chrysophyceae is divided into the following orders for golden algae species according to Guiry and Guiry classification system:

Thallochrysidales order
Hydrurales order
Chromulinales order
Rhizochrysidales order
Hibberdiales order

This is complete details about Guiry and Guiry's classification system of golden algae species.

It should also be noted that these classifications of orders and groups are bound to change and may lead to a newer system of classification whenever further studies and research are conducted on many more species belonging to these groups.

Golden Algae: Members

The phylum, which belongs to golden algae members, is restricted to the core members of the phylum, i.e., golden algae, but originally, they were taken to include all the forms of algae, which are multicellular and diatoms such as brown algae. Further, all these species of algae, divided into several different groups, such as Synurophyceae, Haptophyceae, etc., in which each group represents a specific type of algae that can be brown, red algae, golden algae, etc. These classifications of algae in multiple groups were based on their cell structure and pigmentation that caused their appearance color.

Some of the heterotrophic flagellates, such as the choanoflagellates and bicosoecids, are sometimes considered and related as the associates of the golden algae species. The association and membership of these algal member species will likely be revised further when more species belonging to their group are studied in detail and proper research is conducted on them.

Golden Algae: Evolution

Chrysophytes or Golden Algae were once considered a specialized form of the Blue-green Algae (Cyanobacteria) group because of the presence of the fucoxanthin pigment in them. One of the major reasons for considering them as a specialized form of Blue-green Algae is that many species of golden algae group had a silica capsule. Since golden algae species have a complete fossil record, modern botanists or biologists confirmed that these species are not derived or specialized form of Blue-green Algae but rather an associated ancestor of them that did not possess the capability to photosynthesize. The fossils of most golden algae species completely lacked any type of pigment which is capable of photosynthesis. Moreover, many biologists believe that by forming an endosymbiotic relationship with the Cyanobacteria group containing fucoxanthin pigment, the golden algae group obtained the adaptability to photosynthesize (photosynthesis pigment). That's why it is commonly presumed that the species belonging to the golden algae group are actually evolved from the ancestor species that went through many endosymbiotic events with other algal species.

Golden Algae: Description

The primary cell of the species belonging to the golden algae group contains the following two specialized flagella:

(i) The active feathered flagellum: This flagellum of golden algae species is oriented towards the moving direction, and it contains the mastigonemes, which causes the feathered texture of the flagellum.

(ii) The passive smooth flagellum: This type of flagellum in golden algae species is may be present only in the rudimentary form of some species of them, and it is oriented towards the opposite direction to the movement.

The presence of a siliceous cyst formed endogenously is one of the important characteristics that is usually used to identify the members of the golden algae group that belong to the Chrysophyceae class. The siliceous cyst structure in golden algae species, also called statocyst, stomatocyst, or statospore, usually contains a single pore and globose. The surface of the mature siliceous cyst in most golden algae species may be ornamented with many different structural elements, which are very useful to distinguish these species groups.

Description of Members of Golden Algae group:

Most of the golden algae group members have unicellular flagellate in which it is either one visible flagellum, as in Chromulina species, or sometimes double visible flagella, as in Ochromonas. The Chromulina species of golden algae was first defined in Pascher's classification system and included in the one visible flagella category and the Ochromonas of double flagella category treated in the order Ochromonadales. However, many studies later found that in Chromulina species, a short flagellum was always present, or at least a second basal body was present in them. Therefore, this flagella point was no longer considered as the valid point of distinction between them. Most of these members of the golden algae group have no cell covering, whereas some of them have shells or loricae, such as in Dinobryon. These shells or loricae of these members grow in branched colonies and are sessile. According to the latest classification system, most of the sillicaceous scale members are now placed in a separate group, i.e., the synurids, but earlier, they belonged to the Chromulinales.
Some members of the golden algae group have long branch extension and amoeboid, and contrary to this, they also pass through the flagellate stage of development. Examples of such types of golden algae members are Rhizochrysis and Chrysamoeba. Other than this, Myxochrysis paradoxa is also a golden algae species that is very similar to those found in slime molds because it has a complex life cycle that involves a multinucleate plasmodial stage of development (same as in slime molds). These members of the golden algae group were originally treated and belonged to the order Chrysamoebales, and Rhizochromulina (which is also superficially similar to this order) also belonged here once. But, now Rhizochromulina species have given their own order in the classification system, and this order is based on differences in their structure at the flagellate stage of the development.
Other members of the golden algae group are non-motile, and cells of these members are embedded in mucilage and maybe naked, as in coccoid or in Chrysosaccus, and cells of some of these species are surrounded by a cell wall, as in Chrysosphaera. Some of these species are also parenchymatous or even filamentous in the organization, as in Phaeoplaca. These members were earlier included in various orders according to the older classification systems, and most of them now have their separate groups according to the latest classification system.

Golden Algae: Ecology and distribution

Most of the species that belong to the golden algae group are freshwater habitat species, and all of them are primarily found in lakes and rivers (that are a prominent source of fresh water). The species belonging to the golden algae group are very important contributors to the food web, which is very dynamic in freshwater environments, and thus studies of these species become even more important. Prymnesium parvum is a golden algae species generally associated with harmful algal bloom. This species is also famous for its toxins because the toxins produced by Prymnesium parvum cause fish kills whenever the condition is favorable for amplified algal growth and reproduction, algal blooms are formed. Although, there is no such evidence that indicates that toxins produced by Prymnesium parvum or any other golden algae species can cause any actual threat to mammals or humans who consume the dead fishes (killed because of golden algae's toxin).

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