Zoochlorella (: zoochlorellae) is a colloquial term for any

green algae 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 ...

that lives symbiotically within the body of an aquatic

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

animal or a

protozoa Protozoa (: protozoan or protozoon; alternative plural: protozoans) are a polyphyletic group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic debris. Historically ...

Classification

Zoochlorellae are various genera belonging to the classes Chlorophyceae and

Trebouxiophyceae The Trebouxiophyceae, also known as trebouxiophytes, are a class of green algae, in the division Chlorophyta. Members of this class are single-celled, colonial, or multicellular and are found in freshwater, terrestrial or marine habitats worldwid ...

, historically treated as a single genus ''Zoochlorella'' due to their similar appearance to the genus ''

Chlorella ''Chlorella'' is a genus of about thirteen species of single- celled or colonial green algae of the division Chlorophyta. The cells are spherical in shape, about 2 to 10 μm in diameter, and are without flagella. Their chloroplasts contain t ...

''. However, this genus was found to be

polyphyletic A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...

through

molecular phylogeny Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

, and currently considered '' nomen rejiciendum''. As a consequence, the two species belonging to this obsolete genus have been transferred to different green algal genera. * ''Zoochlorella conductrix'' → '' Micractinium'' * ''Zoochlorella parasitica'' → '' Choricystis''

Origin

The analogy between zoochlorellae and

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 was used by the botanist Konstantin Mereschkowski in 1905 to argue about the symbiotic origin of chloroplasts (then called 'chromatophores', a term used for completely different structures today).Martin W, and Kowallik, K V. 1999, Annotated English translation of Mereschkowsky's 1905 paper 'Über Nature und Ursprung der Chromatophoren im Pflanzenreich'. Eur. J. Phycol., 34: 287-295
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Occurrence

In animals

Zoochlorellae are responsible for the

green Green is the color between cyan and yellow on the visible spectrum. It is evoked by light which has a dominant wavelength of roughly 495570 nm. In subtractive color systems, used in painting and color printing, it is created by a com ...

ish colour of

sea anemone Sea anemones ( ) are a group of predation, predatory marine invertebrates constituting the order (biology), order Actiniaria. Because of their colourful appearance, they are named after the ''Anemone'', a terrestrial flowering plant. Sea anemone ...

tentacle In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work main ...

s. Zoochlorellae and zooxanthellae may both be found in the Pacific coast sea anemones '' Anthopleura elegantissima'' and '' Anthopleura xanthogrammica''.

In protists

Four species of distantly related

testate amoebae Testate amoebae (formerly thecamoebians, Testacea or Thecamoeba) are a polyphyletic group of unicellular amoeboid protists, which differ from naked amoebae in the presence of a test (biology), test that partially encloses the cell, with an apert ...

have independently evolved into obligate mixotrophy through the acquisition of zoochlorellae: '' Hyalosphenia papilio'' and '' Heleopera sphagni'', two lobose amoebae belonging to the order Arcellinida within the phylum

Amoebozoa Amoebozoa is a major Taxonomy (biology), taxonomic group containing about 2,400 described species of Amoeba, amoeboid protists, often possessing blunt, fingerlike, Pseudopod#Morphology, lobose pseudopods and tubular mitochondrial cristae. In trad ...

; '' Archerella flavum'', a member of the Labyrinthulomycetes in

Stramenopiles The stramenopiles, also called heterokonts, are Protist, protists distinguished by the presence of stiff tripartite external hairs. In most species, the hairs are attached to flagella, in some they are attached to other areas of the cellular sur ...

; and '' Placocista spinosa'', a filose amoeba belonging to the order Euglyphida within the phylum

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 ...

. Various

ciliates The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to eukaryotic flagella, but are in general shorter and present in much larger numbers, with a different ...

present zoochlorellae, such as the genera ''

Paramecium ''Paramecium'' ( , , plural "paramecia" only when used as a Common name, vernacular name) is a genus of eukaryotic, unicellular ciliates, widespread in freshwater, brackish, and Ocean, marine environments. Paramecia are often abundant in stagna ...

'', '' Stentor'', '' Climacostomum'', '' Coleps'' and '' Euplotes''. In the centrohelid '' Acanthocystis turfacea'' lives a unique zoochlorella species known as '' Chlorella heliozoae''.

References

Chlorellaceae Trebouxiophyceae genera Monotypic algae genera {{Green algae-stub