Amorphea
are members of a taxonomic supergroup that includes the basal
Amoebozoa
Amoebozoa is a major taxonomic group containing about 2,400 described species of amoeboid protists, often possessing blunt, fingerlike, lobose pseudopods and tubular mitochondrial cristae. In traditional and currently no longer supported classi ...
and
Obazoa
Obazoa (Brown et al., 2013) is a proposed sister clade of Amoebozoa (which together form Amorphea). Obazoa is composed of Breviatea, Apusomonadida and Opisthokonta. The term Obazoa is based on the OBA acronym for Opisthokonta, Breviatea, and Apu ...
. That latter contains the
Opisthokonta, which includes the
Fungi
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
,
Animal
Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
s and the Choanomonada, or
Choanoflagellate
The choanoflagellates are a group of free-living unicellular and colonial flagellate eukaryotes considered to be the closest living relatives of the animals. Choanoflagellates are collared flagellates, having a funnel shaped collar of interconne ...
s. The taxonomic affinities of the members of this clade 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 that the ISP authors and other scientists later rejected.
It includes
amoebozoa
Amoebozoa is a major taxonomic group containing about 2,400 described species of amoeboid protists, often possessing blunt, fingerlike, lobose pseudopods and tubular mitochondrial cristae. In traditional and currently no longer supported classi ...
,
opisthokonts,
and possibly
Apusozoa
The Apusozoa are an Obazoa phylum comprising several genera 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 prese ...
.
Taxonomic revisions within this group
Cavalier-Smith has 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 to ...
, which consists of the subphyla
Apusozoa
The Apusozoa are an Obazoa phylum comprising several genera 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 prese ...
(
Apusomonadida
The Apusomonadida 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, the clade that includ ...
and
Breviatea), and
Varisulca, which includes the subphyla
Diphyllatea,
Discocelida,
Mantamonadidae
The Mantamonadidae are of Motility, free-living heterotrophic flagellates that move primarily by gliding on surfaces (rather than swimming). There is one genus, ''Mantamonas''. It has been suggested previously that the Mantamonadidae be classifi ...
,
Planomonadida
Ancyromonadida or Planomonadida is a small group of biflagellated protists found in the soil and in aquatic habitats, where they feed on bacteria.Cavalier-Smith, T. (2013)Early evolution of eukaryote feeding modes, cell structural diversity, an ...
and
Rigifilida
Rigifilida is a clade of non-ciliate phagotrophic eukaryotes. It consists of two genera: ''Micronuclearia'' and '' Rigifila''.
Characteristics
Cells of rigifilids are covered with either a single or a double-layered submembrane pellicular lamina ...
.
The validity of this proposed taxonomy has yet to be ruled upon by the Society of Protistologists.
Further work by Cavalier-Smith has shown that Sulcozoa is
paraphyletic
In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...
.
Apusozoa also appears to be paraphyletic.
Varisulca has been redefined to include planomonads,
Mantamonas and
Collodictyon
''Collodictyon'' is a genus of single-celled, omnivorous eukaryotes belonging to the collodictyonids, also known as diphylleids. Due to their mix of cellular components, Collodictyonids do not belong to any well-known kingdom (biology), kingdom-l ...
. 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 – Archamoebae, Variosea (paraphyletic) and Mycetozoa (polyphyletic).
In some classifications, the mycetozoan Myxogastria and Dictyostelia are united in Macromycetozoa. ...
and
Lobosa
Lobosa is a taxonomic group of amoebae in the phylum Amoebozoa. Most lobosans possess broad, bluntly rounded pseudopods, although one genus in the group, the recently discovered ''Sapocribrum,'' has slender and threadlike (filose) pseudopodia. ...
. Conosa is divided into the aerobic infraphylum
Semiconosia
Conosa is a grouping of Amoebozoa. It is subdivided into three groups – Archamoebae, Variosea (paraphyletic) and Mycetozoa (polyphyletic).
In some classifications, the mycetozoan Myxogastria and Dictyostelia are united in Macromycetozoa.
...
(
Mycetozoa and
Variosea
Conosa is a grouping of Amoebozoa. It is subdivided into three groups – Archamoebae, Variosea (paraphyletic) and Mycetozoa (polyphyletic).
In some classifications, the mycetozoan Myxogastria and Dictyostelia are united in Macromycetozoa. ...
) 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 sp ...
. 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 cylindrical for ...
, which has predominantly tube-shaped pseudopodia.
Clade
The group includes
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. Bacte ...
cells that, for the most part, have a single emergent
flagellum
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 f ...
, or are amoebae with no flagella. The unikonts include
opisthokonts (
animal
Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
s,
fungi
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
, and related forms) and
Amoebozoa
Amoebozoa is a major taxonomic group containing about 2,400 described species of amoeboid protists, often possessing blunt, fingerlike, lobose pseudopods and tubular mitochondrial cristae. In traditional and currently no longer supported classi ...
. 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 members of the group, and the presumed ancestor, have two flagella.
Enzymes
Another shared trait of bikonts is the fusion of two g ...
. Bikonts include
Archaeplastida (plants and relatives) and
SAR supergroup, the
Cryptista
Cryptista is a clade of algae-like eukaryotes. It is most likely related to Archaeplastida which includes plants and many algae, within the larger group Diaphoretickes.
Although it has sometimes placed along with Haptista in the group Hacrobia, ...
,
Haptista,
Telonemia 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 other ...
nucleotide
Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecules wi ...
s:
carbamoyl phosphate synthase
Carbamoyl phosphate synthetase catalyzes the ATP-dependent synthesis
of carbamoyl phosphate from glutamine () or ammonia () and bicarbonate. This enzyme catalyzes the reaction of ATP and bicarbonate to produce carboxy phosphate and ADP. Carb ...
,
dihydroorotase
Dihydroorotase (, ''carbamoylaspartic dehydrase'', ''dihydroorotate hydrolase'') is an enzyme which converts carbamoyl aspartic acid into 4,5-dihydroorotic acid in the biosynthesis of pyrimidines. It forms a multifunctional enzyme with carbamoyl ...
,
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 (300 ...
. 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. 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 but has remnant mitochondrial genes, and possesses an organelle believed to be a modif ...
'', 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 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 unranked clades