The chlorarachniophytes are a small group of exclusively marine

alga Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular microalgae, suc ...

e widely distributed in tropical and temperate waters. They are typically

mixotrophic A mixotroph is an organism that uses a mix of different sources of energy and carbon, instead of having a single trophic mode, on the continuum from complete autotrophy to complete heterotrophy. It is estimated that mixotrophs comprise more than ...

, ingesting

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

and smaller

protist A protist ( ) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus. Protists do not form a natural group, or clade, but are a paraphyletic grouping of all descendants of the last eukaryotic common ancest ...

s as well as conducting

photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...

. Normally they have the form of small

amoeba An amoeba (; less commonly spelled ameba or amœba; : amoebas (less commonly, amebas) or amoebae (amebae) ), often called an amoeboid, is a type of Cell (biology), cell or unicellular organism with the ability to alter its shape, primarily by ...

e, with branching cytoplasmic extensions that capture prey and connect the cells together, forming a net. These extensions are dependent on the presence of

light Light, visible light, or visible radiation is electromagnetic radiation that can be visual perception, perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400– ...

and polymerization of the

actin Actin is a family of globular multi-functional proteins that form microfilaments in the cytoskeleton, and the thin filaments in muscle fibrils. It is found in essentially all eukaryotic cells, where it may be present at a concentration of ...

cytoskeleton The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including those of bacteria and archaea. In eukaryotes, it extends from the cell nucleus to the cell membrane and is compos ...

. They may also form

flagellate A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes and the ...

zoospore A zoospore is a motile asexual spore that uses a flagellum for locomotion in aqueous or moist environments. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Certain zoospores are ...

s, which characteristically have a single subapical flagellum that spirals backwards around the cell body, and walled coccoid cells. The

chloroplast A chloroplast () is a type of membrane-bound organelle, organelle known as a plastid that conducts photosynthesis mostly in plant cell, plant and algae, algal cells. Chloroplasts have a high concentration of chlorophyll pigments which captur ...

s were presumably acquired by ingesting some

green alga The green algae (: green alga) are a group of chlorophyll-containing autotrophic eukaryotes consisting of the phylum Prasinodermophyta and its unnamed sister group that contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ( ...

. They are surrounded by four membranes, the outermost of which is continuous with the

endoplasmic reticulum The endoplasmic reticulum (ER) is a part of a transportation system of the eukaryote, eukaryotic cell, and has many other important functions such as protein folding. The word endoplasmic means "within the cytoplasm", and reticulum is Latin for ...

, and contain a small

nucleomorph Nucleomorphs are small, vestigial eukaryotic nuclei found between the inner and outer pairs of membranes in certain plastids. They are thought to be vestiges of red and green algal nuclei that were engulfed by a larger eukaryote. Because the nucl ...

between the middle two, which is a remnant of the alga's nucleus. This contains a small amount of

DNA Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...

and divides without forming a

mitotic Mitosis () is a part of the cell cycle in eukaryotic cells in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis is an equational division which gives rise to genetically identical cells in which the t ...

spindle. The origin of the chloroplasts from green algae is supported by their pigmentation, which includes

chlorophyll Chlorophyll 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 allows plants to absorb energy ...

s ''a'' and ''b'', and by genetic similarities. The only other groups of algae that contain nucleomorphs are a few species of

dinoflagellate The Dinoflagellates (), also called Dinophytes, are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered protists. Dinoflagellates are mostly marine plankton, but they are also commo ...

s, which also have plastids originating from green algae, and the

cryptomonad The cryptomonads (or cryptophytes) are a superclass of algae, most of which have plastids. They are traditionally considered a division of algae among phycologists, under the name of Cryptophyta. They are common in freshwater, and also occur ...

s, which acquired their chloroplasts from a

red alga Red algae, or Rhodophyta (, ; ), make up one of the oldest groups of eukaryotic algae. The Rhodophyta comprises one of the largest Phylum, phyla of algae, containing over 7,000 recognized species within over 900 Genus, genera amidst ongoing taxon ...

. The chlorarachniophytes only include five genera, which show some variation in their life-cycles and may lack one or two of the stages described above. Genetic studies place them among the

Cercozoa Cercozoa (now synonymised with Filosa) is a phylum of diverse single-celled eukaryotes. They lack shared morphological characteristics at the microscopic level, and are instead united by phylogeny, molecular phylogenies of rRNA and actin or Ubiqu ...

, a diverse group of amoeboid and amoeboid-like protozoa. The chlorarachniophytes were placed before in the order Rhizochloridales, class

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 ...

(e.g., Smith, 1938), as algae, or in order Rhizochloridea, class Xanthomonadina (e.g., Deflandre, 1956), as protozoa. So far sexual reproduction has only been reported in two species; ''Chlorarachnion reptans'' and ''Cryptochlora perforans''.

Morphology

Phylogeny

Based on Shiratori et al. 2024.

Taxonomy

* Class Chlorarachniophyceae Hibberd & Norris 1984 hlorarachnea Cavalier-Smith 1998; Chlorarachniophyta Hibberd & Norris 1984; Chlorarachnia Cavalier-Smith 1993*::* Genus

incertae sedis or is a term used for a taxonomy (biology), taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...

'' Rhabdamoeba'' Dunkerly 1921 *::** Species '' Rhabdamoeba marina'' Dunkerly 1921 ** Order Minorisida Cavalier-Smith 2017 *** Family Minorisidae Cavalier-Smith 2017 **** Genus '' Minorisa'' Del Campo 2013 ***** Species '' Minorisa minuta'' Del Campo 2013 ** Order Chlorarachniales Ishida & Hara 1996 hlorarachniida Hibberd & Norris 1984*** Family Chlorarachniaceae (Pascher 1939) Ishida & Hara 1996 **** Genus '' Amorphochlora'' Ishida, Yabuki & Ota 2011 ***** Species '' Amorphochlora amoebiformis'' (Ishida & Hara 1996) Ishida, Yabuki & Ota 2011 'Lotharella amoeboformis'' Ishida & Hara 1996**** Genus '' Bigelowiella'' Moestrup 2001 ***** Species '' B. longifila'' Shuhei, Kunihiko & Kenichiro 2007 ***** Species '' B. natans'' Moestrup 2001 **** Genus '' Chlorarachnion'' Geitler 1930 ***** Species '' Chlorarachnion reptans'' Geitler 1930 **** Genus '' Cryptochlora'' Calderon-Saenz & Schnetter 1987 ***** Species '' Cryptochlora perforans'' Calderon-Saenz & Schnetter 1987 **** Genus '' Gymnochlora'' Ishida, Nakayama & Hara 1996 ***** Species '' G. dimorpha'' Ota 2011 ***** Species '' G. stellata'' Ishida, Nakayama & Hara 1996 **** Genus '' Lotharella'' Ishida & Hara 1996 ***** Species '' L. scrobicolata'' Ishida & Hara ***** Species '' L. polymorpha'' Dietz et al. 2003 ***** Species '' L. vacuolata'' Ota & Ishida 2005 ***** Species '' L. oceanica'' Ota 2009 ***** Species '' L. reticulosa'' Ohta 2012 ***** Species '' L. globosa'' (Ishida & Hara 1994) Ishida & Hara 1996 'Chlorarachnion globosum'' Ishida & Hara 1994**** Genus '' Norrisiella'' Ota, Ueda & Ishida 2007 ***** Species '' Norrisiella sphaerica'' Ota, Ueda & Ishida 2007 **** Genus '' Partenskyella'' Ota et al. 2009 ***** Species '' Partenskyella glossopodia'' Ota et al. 2009 **** Genus '' Viridiuvalis'' T.Shiratori, S.Fujita, T.Shimizu & K.Ishida 2017 ***** Species '' Viridiuvalis adhaerens'' T.Shiratori, S.Fujita, T.Shimizu & K.Ishida 2017 File:Chlorarachniophyte, Lotharella globosa, extending a filopodium.png, ''Lotharella globosa'' extending a filopodium (Fp) through a pore of the cell wall (CW) from a walled amoeboid cell. Py: pyrenoid.
Scale bar = 10 μm File:Binary and quaternary cell divisions of a chlorarachniophyte, Lotharella globosa.png, Binary and quaternary cell divisions of ''Lotharella globosa''. Arrowheads indicate the parental cell wall.
Scale bar = 10 μm File:Flagellate cell of a chlorarachniophyte, Lotharella globosa, with a single flagellum and plastid.png, Flagellate cell of ''Lotharella globosa'' with a single flagellum (Fl) and plastid (P)
Scale bar = 10 μm

References

External links

AlgaeBase: Chlorarachniophyta

Tree of Life: Chlorarachniophyta
{{Taxonbar, from=Q136146 Filosa Algal taxonomy