The raphidophytes, formally known as Raphidomonadea or Raphidophyceae (formerly referred to as Chloromonadophyceae and Chloromonadineae), are a small group of

eukaryotic Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bact ...

alga Algae ( , ; : alga ) are any of a large and diverse group of photosynthetic, eukaryotic organisms. The name is an informal term for a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from u ...

e that includes both marine and

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does in ...

species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...

. All raphidophytes are

unicellular A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and ...

, with large cells (50 to 100

μm The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...

), but no

cell walls A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mech ...

. Raphidophytes possess a pair of

flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...

, organised such that both originate from the same invagination (or gullet). One flagellum points forwards, and is covered in hair-like mastigonemes, while the other points backwards across the cell surface, lying within a

ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

groove. Raphidophytes contain numerous

ellipsoid An ellipsoid is a surface that may be obtained from a sphere by deforming it by means of directional scalings, or more generally, of an affine transformation. An ellipsoid is a quadric surface; that is, a surface that may be defined as the ...

chloroplast A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it ...

s, which contain

chlorophyll Chlorophyll (also chlorophyl) is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words , ("pale green") and , ("leaf"). Chlorophyll allow plants to ...

s a, c₁ and c₂. They also make use of accessory pigments including β-carotene and

diadinoxanthin Diadinoxanthin is a pigment found in phytoplankton. It has the formula C40H54O3. It gives rise to the xanthophylls diatoxanthin and dinoxanthin. Diadinoxanthin is a plastid pigment. Plastid pigments include chlorophylls a and c, fucoxanthin, he ...

. Unlike other heterokontophytes, raphidophytes do not possess the photoreceptive organelle (or eyespot) typical of this group. In terms of

ecology Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overl ...

, raphidophytes occur as

photosynthetic Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...

autotroph An autotroph or primary producer is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) using carbon from simple substances such as carbon dioxide,Morris, J. et al. (2019). "Biology: How Life Works", ...

s across a range of aquatic systems. Freshwater species are more common in acidic waters, such as pools in

bog A bog or bogland is a wetland that accumulates peat as a deposit of dead plant materials often mosses, typically sphagnum moss. It is one of the four main types of wetlands. Other names for bogs include mire, mosses, quagmire, and muskeg; a ...

s. Marine species often produce large blooms in summer, particularly in coastal waters. Off the Japanese coast, the resulting

red tide A harmful algal bloom (HAB) (or excessive algae growth) is an algal bloom that causes negative impacts to other organisms by production of natural phycotoxin, algae-produced toxins, mechanical damage to other organisms, or by other means. HABs are ...

s often cause disruption to fish farms, although raphidophytes are not usually responsible for

toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subs ...

blooms. The position of this group varied in former classifications. Some protozoologists treated the chloromonads as an order within the phytoflagellates. Some phycologists classified them with the

Xanthophyceae Yellow-green algae or the Xanthophyceae (xanthophytes) are an important group of heterokont algae. Most live in fresh water, but some are found in marine and soil habitats. They vary from single-celled flagellates to simple colonial and filamen ...

and the

Eustigmatophyceae Eustigmatophytes are a small group (17 genera; ~107 species) of eukaryotic forms of algae that includes marine, freshwater and soil-living species. All eustigmatophytes are unicellular, with coccoid cells and polysaccharide cell walls. Eust ...

in the division Xanthophyta. Others considered them as related to the Chrysophyceae, Dinophyceae, or Cryptophyceae Recently, the heliozoan

Actinophyrida The actinophryids are an order of heliozoa, a polyphyletic array of stramenopiles, having a close relationship with pedinellids and ''Ciliophrys''. They are common in fresh water and occasionally found in marine and soil habitats. Actinophryids ...

was moved to the group.

Taxonomy

Classification based on Cavalier-Smith and Scoble 2013 * Class Raphidomonadea Silva 1980 emend. Cavalier-Smith 2013 aphidophyceae Chadefaud 1950 emend. Silva 1980 s.l.** nplaced genera*** Genus '' Psammamonas'' Grant et al. 2013 *** Genus '' Chloromorum'' Tomas et al. ** Subclass Raphopoda Cavalier-Smith 2013 *** Order Commatiida Cavalier-Smith 1997 **** Family Commatiidae Cavalier-Smith 2013 ***** Genus ''

Commation ''Commation'' is a genus of marine heterotrophic protists closely related to the actinophryids. It contains two species, '' Commation cryoporinum'' and '' Commation eposianum'', discovered in antarctic waters and described in 1993. Currently, t ...

'' Thomsen & Larsen 1993 *** Order

Hartmann 1913 ctinophrydia Kühn 1926; Actinophrydea Hartmann 1913**** Family

Actinosphaeriidae The actinophryids are an order of heliozoa, a polyphyletic array of stramenopiles, having a close relationship with pedinellids and ''Ciliophrys''. They are common in fresh water and occasionally found in marine and soil habitats. Actinophryids ...

Cavalier-Smith 2013 ***** Genus '' Actinosphaerium'' Ritter von Stein 1857 'Camptonema'' Schaudinn 1894; ''Echinosphaerium">Camptonema.html" ;"title="'Camptonema">'Camptonema'' Schaudinn 1894; ''Echinosphaerium'' Hovasse 1965] **** Family Helioraphidae Cavalier-Smith 2013 ***** Genus ''Heliorapha'' Cavalier-Smith 2013 **** Family Actinophryidae Dujardin 1841 ***** Genus '' Actinophrys'' Ehrenberg 1830 'Trichoda'' Müller 1773 nomen oblitum; ''Peritricha (genus)">Peritricha'' Bory de St.Vincent 1824 nomen dubium non Stein 1859">Trichoda">'Trichoda'' Müller 1773 nomen oblitum; ''Peritricha (genus)">Peritricha'' Bory de St.Vincent 1824 nomen dubium non Stein 1859 ** Subclass Raphidophycidae Cavalier-Smith 2013 [Raphidophyceae Chadefaud 1950 emend. Silva 1980 s.s.; Chloromonadophyceae Rothmaler 1951; Raphidophyta] *** Order Raphidomonadales hattonellales Throndsen 1993; Chloromonadida; Chloromonadales; Raphidomonadida Heywood & Leedale 1983; Chloromonadina Klebs 1892**** Genus '' Viridilobus'' Demir-Hilton et al. 2012 **** Family Fibrocapsaceae Cavalier-Smith 2013 ***** Genus ''

Fibrocapsa ''Fibrocapsa'' is a genus of algae belonging to the family Fibrocapsaceae. Species: * ''Fibrocapsa japonica'' S.Toriumi & H.Takano References {{Taxonbar, from=Q21368614 Ochrophyta Heterokont genera ...

'' Toriumi & Takano 1973 **** Family Haramonadaceae Cavalier-Smith 2013 ***** Genus '' Haramonas'' Horiguchi 1996 **** Family Chattonellaceae Throndsen ***** Genus '' Oltmannsia'' Schiller 1925 ***** Genus '' Chlorinimonas'' Yamaguchi et al. 2010 ***** Genus ''

Heterosigma ''Heterosigma akashiwo'' is a species of microscopic algae of the class Raphidophyceae. It is a swimming marine alga that episodically forms toxic surface aggregations known as harmful algal bloom. The species name ''akashiwo'' is from the Jap ...

'' Hada 1967 ex Hara & Chihara 1987 ***** Genus '' Chattonella'' Biecheler 1936 'Hornellia'' Subrahmanyan 1954; ''Hemieutreptia">Hornellia.html" ;"title="'Hornellia">'Hornellia'' Subrahmanyan 1954; ''Hemieutreptia'' Hada 1974] **** Family Vacuolariaceae ***** Genus ''Swirenkoiamonas'' Skvortzov 1968 ***** Genus ''Vacuolaria'' Cienkowski 1870 ***** Genus ''Merotricha'' Mereschkowsky 1877 ***** Genus ''

Gonyostomum ''Gonyostomum'' is a genus of freshwater algae in the class Raphidophyceae. They include the species '' Gonyostomum semen'', which causes nuisance algal blooms. References {{Taxonbar, from=Q5582133 Ochrophyta Heterokont genera ...

'' Diesing 1866

References

{{Taxonbar, from=Q134928 Ochrophyta