Cercozoa is a phylum of diverse single-celled
eukaryotes.
They lack shared morphological characteristics at the microscopic level,
and are instead defined by
molecular phylogenies
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 ...
of
rRNA
Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes. Ribosomal RNA is transcribed from ribosoma ...
and
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 ov ...
or
polyubiquitin.
They were the first major
eukaryotic
Eukaryotes () are organisms whose Cell (biology), cells have a cell nucleus, 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 ...
group to be recognized mainly through
molecular phylogenies
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 ...
.
They are the natural predators of many species of
microbacteria and
Archea
Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaeb ...
. They are closely related to the phylum
Retaria
Retaria is a clade within the supergroup Rhizaria containing the Foraminifera and the Radiolaria. In 2019, the Retaria were recognized as a basal Rhizaria group, as sister of the Cercozoa
Cercozoa is a phylum of diverse single-celled eukaryote ...
, comprising amoeboids that usually have complex shells, and together form a supergroup called
Rhizaria
The Rhizaria are an ill-defined but species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are all non-photosynthethic, but many forami ...
.
Characteristics
The group includes most
amoeboid
An amoeba (; less commonly spelled ameba or amœba; plural ''am(o)ebas'' or ''am(o)ebae'' ), often called an amoeboid, is a type of cell or unicellular organism with the ability to alter its shape, primarily by extending and retracting pseudopo ...
s and
flagellates that feed by means of filose pseudopods. These may be restricted to part of the cell surface, but there is never a true
cytostome
A cytostome (from ''cyto-'', cell and ''stome-'', mouth) or cell mouth is a part of a cell specialized for phagocytosis, usually in the form of a microtubule-supported funnel or groove. Food is directed into the cytostome, and sealed into vacuol ...
or mouth as found in many other protozoa. They show a variety of forms
and have proven difficult to define in terms of structural characteristics, although their unity is strongly supported by
phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
studies.
Diversity
Some cercozoans are grouped by whether they are "filose" or "reticulose" in the behavior of their
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 com ...
when moving:
*Filose, meaning their
pseudopod
A pseudopod or pseudopodium (plural: pseudopods or pseudopodia) is a temporary arm-like projection of a eukaryotic cell membrane that is emerged in the direction of movement. Filled with cytoplasm, pseudopodia primarily consist of actin filament ...
s develop as
filopodia
Filopodia (singular filopodium) are slender cytoplasmic projections that extend beyond the leading edge of lamellipodia in migrating cells. Within the lamellipodium, actin ribs are known as ''microspikes'', and when they extend beyond the lame ...
. For example:
**
Euglyphid
The euglyphids are a prominent group of filose amoebae that produce shells or tests from siliceous scales, plates, and sometimes spines. These elements are created within the cell and then assembled on its surface in a more or less regular arran ...
s, filose amoebae with shells of
siliceous
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...
scales or plates, which are commonly found in soils, nutrient-rich waters, and on aquatic plants.
**''
Gromia
''Gromia'' is a genus of protists, closely related to foraminifera, which inhabit marine and freshwater environments. It is the only genus of the family Gromiidae. ''Gromia'' are ameboid, producing filose pseudopodia that extend out from the ce ...
'', a shelled amoeba.
**
Tectofilosid
The tectofilosids are a group of filose amoebae with shells. These are composed of organic materials and sometimes collected debris, in contrast to the euglyphids, which produce shells from siliceous scales. The shell usually has a single openi ...
s, filose amoebae that produce organic shells.
**
Cercomonad
Cercomonads are small flagellates, widespread in aqueous habitats and common in soils.
Characteristics
The cells are generally around 10 μm in length, without any shell or covering. They produce filose pseudopods to capture bacteria, but do n ...
s, common soil-dwelling amoeboflagellates.
*Reticulose, meaning they form a reticulating net of
pseudopod
A pseudopod or pseudopodium (plural: pseudopods or pseudopodia) is a temporary arm-like projection of a eukaryotic cell membrane that is emerged in the direction of movement. Filled with cytoplasm, pseudopodia primarily consist of actin filament ...
s. For example:
**
Chlorarachniophytes, set apart by the presence of
chloroplasts bound by four membranes and still possess a vestigial nucleus, called a nucleomorph. As such, they have been of great interest to researchers studying the endosymbiotic origins of organelles.
Other important ecological groups are:
*
Granofilosea
Granofilosea is a class of cercozoans in the subphylum Filosa.
Three groups that were traditionally considered heliozoans belong here: the Heliomonadida, Desmothoracida and Gymnosphaerida, which were recently grouped into the new class of Gra ...
, comprising several groups traditionally considered
heliozoa
Heliozoa, commonly known as sun-animalcules, are microbial eukaryotes ( protists) with stiff arms ( axopodia) radiating from their spherical bodies, which are responsible for their common name. The axopodia are microtubule-supported projections f ...
such as
Heliomonadida
The Heliomonadida (formerly Dimorphida) are a small group of heliozoan amoeboids that are unusual in possessing flagella throughout their life cycle.
Classification
Genetic studies place them among the Cercozoa, a group including various other ...
,
Desmothoracida and
Gymnosphaerida.
*
Phaeodaria
Phaeodarea, or Phaeodaria, is a group of amoeboid cercozoan organisms. They are traditionally considered radiolarians, but in molecular trees do not appear to be close relatives of the other groups, and are instead placed among the Cercozoa. They ...
, marine protozoa previously considered
radiolaria
The Radiolaria, also called Radiozoa, are protozoa of diameter 0.1–0.2 mm that produce intricate mineral skeletons, typically with a central capsule dividing the cell into the inner and outer portions of endoplasm and ectoplasm. The el ...
ns.
[
*]Phytomyxea
The Phytomyxea are a class of parasites that are cosmopolitan, obligate biotrophic protist parasites of plants, diatoms, oomycetes and brown algae. They are divided into the orders Plasmodiophorida (ICZN, or Plasmodiophoromycota, ICBN) and Phag ...
, parasites of mostly plants, including the fungi-like plasmodiophores.
* Ascetosporea, parasites of mostly marine invertebrates.
Ecology
As well as being highly diverse in morphology
Morphology, from the Greek and meaning "study of shape", may refer to:
Disciplines
* Morphology (archaeology), study of the shapes or forms of artifacts
* Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...
and physiology
Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...
, Cercozoa also shows high ecological diversity
Ecosystem diversity deals with the variations in ecosystems within a geographical location and its overall impact on human existence and the environment.
Ecosystem diversity addresses the combined characteristics of biotic properties (biodiver ...
. The phylum Cercozoa includes many of the most abundant and ecologically significant protozoa in soil
Soil, also commonly referred to as earth or dirt
Dirt is an unclean matter, especially when in contact with a person's clothes, skin, or possessions. In such cases, they are said to become dirty.
Common types of dirt include:
* Debri ...
, marine and freshwater ecosystems.
Soil-dwelling cercozoans are one of the dominant groups of free-living eukaryotic microorganisms found in temperate
In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout ...
soils, accounting for around 30% of identifiable protozoan DNA in arid or semi-arid soils and 15% in more humid soils. In transcriptomic analyses they account for 40-60% of all identifiable protozoan RNA found in forest and grassland soils. They also comprise 9-24% of all operational taxonomic unit
An Operational Taxonomic Unit (OTU) is an operational definition used to classify groups of closely related individuals. The term was originally introduced in 1963 by Robert R. Sokal and Peter H. A. Sneath in the context of numerical taxonomy, w ...
s found in the ocean floor
The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as 'seabeds'.
The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...
.
Some cercozoa are coprophilic or coprozoic, meaning they use feces as a source of nutrients or as transport through animal hosts. The faecal habitat is an understudied reservoir of microbial eukaryotic diversity, dominated by amoeboflagellates from the phylum Cercozoa. Strongly coprophilic examples of cercozoa are the flagellates '' Cercomonas'', '' Proleptomonas'' and ''Helkesimastix
Cercomonads are small flagellates, widespread in aqueous habitats and common in soils.
Characteristics
The cells are generally around 10 μm in length, without any shell or covering. They produce filose pseudopods to capture bacteria, but do n ...
'', and the sorocarp
A sorocarp (from the Greek word ''soros'' "a heap" + ''karpos'' "fruit") is the fruiting body characteristic of certain cellular slime moulds (e.g., Dictyosteliida). Each sorocarp consists of both a sorophore (stalk) and a sorus.Lawrence, E. 2005 ...
ic amoeba '' Guttulinopsis''. Many new cercozoan lineages, especially among sarcomonad
The sarcomonads () or class Sarcomonadea are a group of amoeboid biciliate protists in the phylum Cercozoa. They are characterized by a propensity to move through gliding on their posterior cilium or through filopodia, a lack of scales or e ...
s, have been discovered through phylogenetic sampling of feces because they appear preferentially in this medium.
Cercozoan bacterivore A bacterivore is an organism which obtains energy and nutrients primarily or entirely from the consumption of bacteria. The term is most commonly used to describe free-living, heterotrophic, microscopic organisms such as nematodes as well as many s ...
s (i.e. predator
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...
s of bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
) are highly diverse and important in the plant phyllosphere, the leaf surfaces of plants. Particularly sarcomonad
The sarcomonads () or class Sarcomonadea are a group of amoeboid biciliate protists in the phylum Cercozoa. They are characterized by a propensity to move through gliding on their posterior cilium or through filopodia, a lack of scales or e ...
s, with their ability to cyst
A cyst is a closed sac, having a distinct envelope and division compared with the nearby tissue. Hence, it is a cluster of cells that have grouped together to form a sac (like the manner in which water molecules group together to form a bubble) ...
, feed and multiply within hours, are perfectly adapted to the fluctuating environmental factors in the phyllosphere. Their predation causes shifts in the bacterial communities: they reduce populations of alphaproteobacteria
Alphaproteobacteria is a class of bacteria in the phylum Pseudomonadota (formerly Proteobacteria). The Magnetococcales and Mariprofundales are considered basal or sister to the Alphaproteobacteria. The Alphaproteobacteria are highly diverse and ...
and betaproteobacteria
Betaproteobacteria are a class of Gram-negative bacteria, and one of the eight classes of the phylum Pseudomonadota (synonym Proteobacteria).
The ''Betaproteobacteria'' are a class comprising over 75 genera and 400 species of bacteria. Togeth ...
, which are less resistant to their grazing, in favour of other bacterial populations such as gammaproteobacteria.
Phylogeny
The initial molecular phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
analyses of Cercozoa, based on ribosomal RNA
Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes. Ribosomal RNA is transcribed from ribosom ...
and tubulin
Tubulin in molecular biology can refer either to the tubulin protein superfamily of globular proteins, or one of the member proteins of that superfamily. α- and β-tubulins polymerize into microtubules, a major component of the eukaryotic cytoske ...
s, recognized two subphyla, Endomyxa
Endomyxa is a subphylum of Rhizaria
The Rhizaria are an ill-defined but species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are a ...
and Filosa, and showed a close relationship with phylum Retaria
Retaria is a clade within the supergroup Rhizaria containing the Foraminifera and the Radiolaria. In 2019, the Retaria were recognized as a basal Rhizaria group, as sister of the Cercozoa
Cercozoa is a phylum of diverse single-celled eukaryote ...
.
However, the monophyly
In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...
of the group was still uncertain. Posterior phylogenomic
Phylogenomics is the intersection of the fields of evolution and genomics. The term has been used in multiple ways to refer to analysis that involves genome data and evolutionary reconstructions. It is a group of techniques within the larger fields ...
analyses consistently recovered Cercozoa as a paraphyletic group, and Endomyxa
Endomyxa is a subphylum of Rhizaria
The Rhizaria are an ill-defined but species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are a ...
was often clustered with Retaria
Retaria is a clade within the supergroup Rhizaria containing the Foraminifera and the Radiolaria. In 2019, the Retaria were recognized as a basal Rhizaria group, as sister of the Cercozoa
Cercozoa is a phylum of diverse single-celled eukaryote ...
. As a result, the current taxonomy of Rhizaria places Endomyxa
Endomyxa is a subphylum of Rhizaria
The Rhizaria are an ill-defined but species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are a ...
inside the phylum Retaria
Retaria is a clade within the supergroup Rhizaria containing the Foraminifera and the Radiolaria. In 2019, the Retaria were recognized as a basal Rhizaria group, as sister of the Cercozoa
Cercozoa is a phylum of diverse single-celled eukaryote ...
instead of Cercozoa, which has therefore become synonymous with Filosa.
Despite the taxonomic change of Endomyxa
Endomyxa is a subphylum of Rhizaria
The Rhizaria are an ill-defined but species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are a ...
into phylum Retaria
Retaria is a clade within the supergroup Rhizaria containing the Foraminifera and the Radiolaria. In 2019, the Retaria were recognized as a basal Rhizaria group, as sister of the Cercozoa
Cercozoa is a phylum of diverse single-celled eukaryote ...
, thanks to better phylogenomic sampling a 2019 analysis recovered phylum Cercozoa as a monophyletic group, with Endomyxa
Endomyxa is a subphylum of Rhizaria
The Rhizaria are an ill-defined but species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are a ...
being the sister group to Filosa. In the same analysis, Endomyxa
Endomyxa is a subphylum of Rhizaria
The Rhizaria are an ill-defined but species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are a ...
, Filosa, Reticulofilosa and Monadofilosa are proven to be monophyletic too.
In addition to Endomyxa
Endomyxa is a subphylum of Rhizaria
The Rhizaria are an ill-defined but species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are a ...
and Filosa, a variety of clades
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
inside Cercozoa have been discovered in other analyses and have slowly been described and named, such as Tremulida (previously known as Novel Clade 11) and Aquavolonida (Novel Clade 10), although their specific positions among the two main cercozoan subphyla have yet to be refined.
Classification
The classification of Cercozoa as revised in 2018, with the addition of Endomyxa
Endomyxa is a subphylum of Rhizaria
The Rhizaria are an ill-defined but species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are a ...
:
Gallery
File:Cercomonas sp.jpg, ''Cercomonas'' sp. (Cercozoa: Cercomonadida)
File:Ebria_tripartita.jpg, ''Ebria'' sp. (Cercozoa: Ebridea
The Ebridea is a group of phagotrophic flagellate eukaryotes present in marine coastal plankton communities worldwide. ''Ebria tripartita'' is one of two (possibly four) described extant species in the Ebridea.
Members of this group are named for ...
)
File:Rhipidodendron splendidum.jpg, ''Rhipidodendron'' sp. (Cercozoa: Spongomonadea)
File:Euglypha_sp.jpg, ''Euglypha'' sp. (Cercozoa: Euglyphida
The euglyphids are a prominent group of filose amoebae that produce shells or tests from siliceous scales, plates, and sometimes spines. These elements are created within the cell and then assembled on its surface in a more or less regular arran ...
)
File:Haeckel Phaeodaria 1.jpg, Phaeodarians (Cercozoa: Phaeodarea)
File:Clathrulina elegans - - Print - Iconographia Zoologica - Special Collections University of Amsterdam - UBAINV0274 113 04 0030.tif, ''Clathrulina elegans
''Clathrulina elegans'' is a species of heliozoan eukaryote
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 Eukaryot ...
'' (Cercozoa: Desmothoracida)
File:Chlorarachnion_reptans.jpg, '' Chlorarachnion'' sp. (Cercozoa: ( Chlorarachniophyta)
File:Vampyrella lateritia.jpg, ''Vampyrella'' sp. (Cercozoa: Vampyrellidae)
File:Orciraptor-gr1c.jpg, ''Orciraptor agilis'' ( Viridiraptoridae) attacking '' Mougeotia'' sp. (Zygnemataceae
The Zygnemataceae are a family of filamentous or unicellular, uniseriate (unbranched) green algae. The filaments are septated and reproduction is by conjugation; ''Spirogyra'' is commonly used in schools to demonstrate this kind of reproductio ...
)
File:Die_Gartenlaube_(1890)_b_083.jpg, ''Gromia
''Gromia'' is a genus of protists, closely related to foraminifera, which inhabit marine and freshwater environments. It is the only genus of the family Gromiidae. ''Gromia'' are ameboid, producing filose pseudopodia that extend out from the ce ...
'' (Cercozoa: Gromiidea
Gromiida is an order of cercozoans. It is the only order in the class Gromiidea.
Taxonomy
Class Gromiidea Cavalier-Smith 2003 sensu Bass et al. 2009
* Order Gromiida Claparède & Lachmann 1856 s.s.
** Family Gromiidae Ruess 1862 romiina Dela ...
)
File:Powdery scab (Spongospora subterranea) of potatoes (1914) (14577838889).jpg, Powdery scab
Powdery scab is a disease of potato tubers. It is caused by the cercozoan ''Spongospora subterranea'' f. sp. ''subterranea'' and is widespread in potato growing countries. Symptoms of powdery scab include small lesions in the early stages of th ...
(Cercozoa: Plasmodiophorida)
File:Auranticordis_quadriverberis_1a.jpg, '' Auranticordis'' (Cercozoa: Marimonadida)
References
External links
Tree of Life
Cercozoa
phylogeny of Phaeodarea
{{Taxonbar, from=Q500497
SAR supergroup phyla
Taxa named by Thomas Cavalier-Smith