Eustigmatophytes are a small group (17

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomencla ...

; ~107

species In biology, a species is the basic unit of 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 the appropriate ...

) 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 ...

forms of

alga Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mi ...

e that includes marine,

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 includ ...

and soil-living species. All eustigmatophytes 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 coccoid cells and

polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with w ...

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 ...

. Eustigmatophytes contain one or more yellow-green

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 in ...

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 ...

a and the accessory pigments violaxanthin and

β-carotene β-Carotene is an organic, strongly coloured red-orange pigment abundant in fungi, plants, and fruits. It is a member of the carotenes, which are terpenoids (isoprenoids), synthesized biochemically from eight isoprene units and thus having 4 ...

. Eustigmatophyte zoids (

gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce ...

s) possess a single or 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 fro ...

, originating from the apex of the cell. Unlike other

heterokont Heterokonts are a group of protists (formally referred to as Heterokonta, Heterokontae or Heterokontophyta). The group is a major line of eukaryotes. Most are algae, ranging from the giant multicellular kelp to the unicellular diatoms, which ...

ophytes, eustigmatophyte zoids do not have typical photoreceptive organelles (or eyespots); instead an orange-red eyespot outside a chloroplast is located at the anterior end of the zoid. Ecologically, eustigmatophytes 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 Work ...

s across a range of systems. Most eustigmatophyte genera live in freshwater or in soil, although ''

Nannochloropsis ''Nannochloropsis'' is a genus of algae comprising six known species. The genus in the current taxonomic classification was first termed by Hibberd (1981). The species have mostly been known from the marine environment but also occur in fresh and ...

'' contains marine species of

picophytoplankton Photosynthetic picoplankton or picophytoplankton is the fraction of the phytoplankton performing photosynthesis composed of cells between 0.2 and 2 µm in size (picoplankton). It is especially important in the central oligotrophic regions of ...

(2–4

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 Uni ...

). The class was erected to include some algae previously classified in the Xanthophyceae.

Classification

* Class Eustigmatophyceae Hibberd & Leedale 1970 ** Order Eustigmatales Hibberd 1981 *** Genus '' Paraeustigmatos'' Fawley, Nemcová, & Fawley 2019 *** Family Eustigmataceae Hibberd 1981 hlorobothryaceae Pascher 1925; Pseudocharaciopsidaceae Lee & Bold ex Hibberd 1981**** Genus ?'' Ellipsoidion'' Pascher 1937 **** Genus ''

Chlorobotrys ''Chlorobotrys'' is a genus of algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthesis, photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct ...

'' Bohlin 1901 **** Genus '' Eustigmatos'' Hibberd 1981 **** Genus '' Pseudocharaciopsis'' Lee & Bold 1973 **** Genus '' Pseudostaurastrum'' Chodat 1921 **** Genus '' Vischeria'' Pascher 1938 - 16 spp. *** Family Monodopsidaceae Hibberd 1981 oboceae Hegewald 2007**** Genus '' Microchloropsis'' Fawley, Jameson & Fawley 2015 **** Genus '' Monodopsis'' Hibberd 1981 **** Genus ''

'' Hibberd 1981 **** Genus '' Pseudotetraedriella'' Hegewald & Padisák 2007 *** Family Neomonodaceae Amaral et al. 2020 **** Genus ?'' Botryochloropsis'' Preisig & Wilhelm 1989 **** Genus '' Characiopsiella'' Amaral et al. 2020 **** Genus '' Munda'' Amaral et al. 2020 **** Genus '' Neomonodus'' Amaral et al. 2020 **** Genus '' Pseudellipsoidion'' Neustupa & Nemková 2001 ** Order Goniochloridales Fawley, Elias & Fawley 2013 *** Family Goniochloridaceae **** Genus '' Goniochloris'' Geitler 1928 **** Genus '' Pseudostaurastrum'' Chodat 1921 **** Genus '' Tetraedriella'' Pascher 1930 **** Genus '' Trachydiscus'' H.Ettl 1964 **** Genus '' Vacuoliviride'' Nakayama et al. 2015

Phylogeny

Phylogeny of Eustigmatophyceae based on the work of Amaral et al 2020

References

Ochrophyta Heterokont classes Algae classes {{Heterokont-stub