Amorphea
is a taxonomic
supergroup that includes the basal
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 ...
and
Obazoa
Obazoa is a proposed sister clade of Amoebozoa (which together form Amorphea). The term Obazoa is based on the OBA acronym for Opisthokonta, Breviatea, and Apusomonadidae, the group's three constituent clades.
Determining the placement of Bre ...
. That latter contains the
Opisthokont
The opisthokonts () are a broad group of eukaryotes, including both the animal and fungus kingdoms. The opisthokonts, previously called the "Fungi/Metazoa group", are generally recognized as a clade. Opisthokonts together with Apusomonadida and ...
a, which includes the
fungi
A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...
,
animals
Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia (). With few exceptions, animals consume organic material, breathe oxygen, have myocytes and are able to move, can reproduce sexually, and grow from a ...
and the
choanoflagellate
Choanoflagellates are a group of free-living unicellular and colonial flagellate eukaryotes considered to be the closest living relatives of animals. The name refers to the characteristic funnel-shaped "collar" of interconnected microvilli and ...
s. The
taxonomic
280px, Generalized scheme of taxonomy
Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme of classes (a taxonomy) and the allocation ...
affinities of the members of this
clade
In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
were originally described and proposed by
Thomas Cavalier-Smith
Thomas (Tom) Cavalier-Smith, FRS, FRSC, NERC Professorial Fellow (21 October 1942 – 19 March 2021), was a professor of evolutionary biology in the Department of Zoology, at the University of Oxford.
His research has led to discov ...
in 2002.
The International Society of Protistologists, the recognised body for taxonomy of protozoa, recommended in 2012 that the term Unikont be changed to Amorphea because the name "Unikont" is based on a hypothesized
synapomorphy
In phylogenetics, an apomorphy (or derived trait) is a novel Phenotypic trait, character or character state that has evolution, evolved from its ancestral form (or Plesiomorphy and symplesiomorphy, plesiomorphy). A synapomorphy is an apomorphy sh ...
that the ISOP authors and other scientists later rejected.
It includes
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 ...
,
opisthokont
The opisthokonts () are a broad group of eukaryotes, including both the animal and fungus kingdoms. The opisthokonts, previously called the "Fungi/Metazoa group", are generally recognized as a clade. Opisthokonts together with Apusomonadida and ...
s,
and
apusomonads.
Taxonomic revisions within this group
Thomas Cavalier-Smith
Thomas (Tom) Cavalier-Smith, FRS, FRSC, NERC Professorial Fellow (21 October 1942 – 19 March 2021), was a professor of evolutionary biology in the Department of Zoology, at the University of Oxford.
His research has led to discov ...
proposed two new phyla:
Sulcozoa
Podiates (Cavalier-Smith, 2012, excl. Ancyromonadida) are a proposed clade containing the Amorphea (incl. Opisthokonta, Amoebozoa, apusomonads and breviates) and the organisms now assigned to the clade CRuMs. Ancyromonadida does not appear ...
, which consists of the subphyla
Apusozoa
The Apusozoa are a paraphyletic phylum of flagellate eukaryotes. They are usually around 5–20 μm in size, and occur in soils and aquatic habitats, where they feed on bacteria. They are grouped together based on the presence of an organic shel ...
(
Apusomonadida
The apusomonads (family Apusomonadidae) are a group of protozoan zooflagellates that glide on surfaces, and mostly consume prokaryotes. They are of particular evolutionary interest because they appear to be the sister group to the Opisthokonts ...
and
Breviatea
Breviatea, commonly known as breviate amoebae, are a group of free-living, amitochondriate protists with uncertain phylogenetic position. They are biflagellate, and can live in anaerobic (oxygen-free) environments. They are currently placed in ...
), and
Varisulca
Varisulca was a proposed basal Podiate taxon. It encompassed several lineages of heterotrophic protists, most notably the ancyromonads (planomonads), collodictyonids (diphylleids), rigifilids (''Rigifila'', ''Micronuclearia'') and mantamona ...
, which includes the subphyla
Diphyllatea,
Discocelida,
Mantamonadidae
Mantamonads are a group of free-living heterotrophic flagellates that move primarily by gliding on surfaces (rather than swimming). They are classified as one genus ''Mantamonas'' in the monotypic family Mantamonadidae, order Mantamonadida, cl ...
,
Planomonadida and
Rigifilida.
Further work by Cavalier-Smith showed that Sulcozoa is
paraphyletic
Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...
.
Apusozoa also appears to be paraphyletic.
Varisulca
Varisulca was a proposed basal Podiate taxon. It encompassed several lineages of heterotrophic protists, most notably the ancyromonads (planomonads), collodictyonids (diphylleids), rigifilids (''Rigifila'', ''Micronuclearia'') and mantamona ...
has been redefined to include planomonads,
Mantamonas and
Collodictyon. A new taxon has been created -
Glissodiscea - for the planomonads and
Mantamonas. Again, the validity of this revised taxonomy awaits confirmation.
Amoebozoa seems to be monophyletic with two major branches:
Conosa
Conosa is a grouping of Amoebozoa. It is subdivided into three groups: Archamoeba, Variosea and Mycetozoa.
In some classifications, the mycetozoan Myxogastria and Dictyostelia are united in Macromycetozoa (= Eumycetozoa).
Conosa includes t ...
and
Lobosa. Conosa is divided into the aerobic infraphylum
Semiconosia (
Mycetozoa
Mycetozoa is a polyphyletic grouping of slime molds. It was originally thought to be a monophyletic clade, but in 2010 it was discovered that protostelia are a polyphyletic group within Conosa.
Classification
It can be divided into dictyoste ...
and
Variosea
Conosa is a grouping of Amoebozoa. It is subdivided into three groups: Archamoeba, Variosea and Mycetozoa.
In some classifications, the mycetozoan Myxogastria and Dictyostelia are united in Macromycetozoa (= Eumycetozoa).
Conosa includes t ...
) and secondarily anaerobic
Archamoebae
The Archamoebae are a group of protists originally thought to have evolved before the acquisition of mitochondria by eukaryotes. They include genera that are internal parasites or commensals of animals ('' Entamoeba'' and '' Endolimax''). A few ...
. Lobosa consists entirely of non-flagellated lobose amoebae and has been divided into two classes:
Discosea
Discosea is a class of Amoebozoa, consisting of naked amoebae with a flattened, discoid body shape. Members of the group do not produce tubular or subcylindrical pseudopodia, like amoebae of the class Tubulinea. When a discosean is in motion, a ...
, which have flattened cells, and
Tubulinea
The Tubulinea are a major grouping of Amoebozoa, including most of the more familiar amoebae genera like ''Amoeba'', '' Arcella'', '' Difflugia'' and '' Hartmannella''.
Characteristics
During locomotion most Tubulinea have a roughly cylindrica ...
, which has predominantly tube-shaped pseudopodia.
Clade
The group includes
eukaryotic
The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...
cells that, for the most part, have a single emergent
flagellum
A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...
, or are amoebae with no flagella. The unikonts include
opisthokonts
The opisthokonts () are a broad group of eukaryotes, including both the animal and fungus kingdoms. The opisthokonts, previously called the "Fungi/Metazoa group", are generally recognized as a clade. Opisthokonts together with Apusomonadida and ...
(
animal
Animals are multicellular, eukaryotic organisms in the Biology, biological Kingdom (biology), kingdom Animalia (). With few exceptions, animals heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, ...
s,
fungi
A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...
, and related forms) and
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 ...
. By contrast, other well-known eukaryotic groups, which more often have two emergent flagella (although there are many exceptions), are often referred to as
bikonts
A bikont ("two flagella") is any of the eukaryotic organisms classified in the group Bikonta. Many single-celled and multi-celled organisms are members of the group, and these, as well as the presumed ancestor, have two flagella.
Enzymes
Anothe ...
. Bikonts include
Archaeplastida
The Archaeplastida (or kingdom Plantae '' sensu lato'' "in a broad sense"; pronounced ) are a major group of eukaryotes, comprising the photoautotrophic red algae (Rhodophyta), green algae, land plants, and the minor group glaucophytes. It als ...
(plants and relatives) and
SAR supergroup, the
Cryptista
Cryptista is a clade of alga-like eukaryotes. It is most likely related to Archaeplastida which includes plants and many algae, within the larger group Diaphoretickes.
Other characteristic features of cryptophyte mtDNAs include large syntenic ...
,
Haptista
Haptista is a proposed group of protists made up of centrohelids and haptophytes. Phylogenomic studies indicate that Haptista, together with ''Ancoracysta twista'', forms a sister clade to the SAR supergroup#Internal phylogeny, TSAR Supergroup (b ...
,
Telonemia
Telonemia is a phylum of microscopic eukaryotes commonly known as telonemids. They are unicellular free-living flagellates with a unique combination of Cell (biology), cell structures, including a highly complex cytoskeleton unseen in other eu ...
and
Picozoa
Picozoa, Picobiliphyta, Picobiliphytes, or Biliphytes are protists of a phylum of marine unicellular heterotrophic eukaryotes with a size of less than about 3 micrometers. They were formerly treated as eukaryotic algae and the smallest member of ...
.
Characteristics
The unikonts have a triple-gene fusion that is lacking in the bikonts. The three genes that are
fused together in the unikonts, but not bacteria or bikonts, encode enzymes for synthesis of the
pyrimidine
Pyrimidine (; ) is an aromatic, heterocyclic, organic compound similar to pyridine (). One of the three diazines (six-membered heterocyclics with two nitrogen atoms in the ring), it has nitrogen atoms at positions 1 and 3 in the ring. The oth ...
nucleotide
Nucleotides are Organic compound, organic molecules composed of a nitrogenous base, a pentose sugar and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both o ...
s:
carbamoyl phosphate synthase,
dihydroorotase,
aspartate carbamoyltransferase
Aspartate carbamoyltransferase (also known as aspartate transcarbamoylase or ATCase) catalyzes the first step in the pyrimidine biosynthetic pathway ().
In '' E. coli'', the enzyme is a multi- subunit protein complex composed of 12 subunits ( ...
. This must have involved a double fusion, a rare pair of events, supporting the shared ancestry of Opisthokonta and Amoebozoa.
Cavalier-Smith
originally proposed that unikonts ancestrally had a single flagellum and single
basal body
A basal body (synonymous with basal granule, kinetosome, and in older cytological literature with blepharoplast) is a protein structure found at the base of a eukaryotic undulipodium (cilium or flagellum). The basal body was named by Theodor Wi ...
. This is unlikely, however, as flagellated opisthokonts, as well as some flagellated Amoebozoa, including ''
Breviata
''Breviata anathema'' is a single-celled flagellate amoeboid eukaryote, previously studied under the name '' Mastigamoeba invertens''. The cell lacks mitochondria, much like the pelobionts to which the species was previously assigned, but has rem ...
'', actually have two basal bodies, as in typical 'bikonts' (even though only one is flagellated in most unikonts). This paired arrangement can also be seen in the organization of
centrioles
In cell biology a centriole is a cylindrical organelle composed mainly of a protein called tubulin. Centrioles are found in most eukaryotic cells, but are not present in conifers ( Pinophyta), flowering plants ( angiosperms) and most fungi, an ...
in typical animal cells. In spite of the name of the group, the common ancestor of all 'unikonts' was probably a cell with two basal bodies.
References
External links
* Tree of Life.org
{{Taxonbar, from=Q474156, from2=Q964455
Eukaryote taxa