Conosa is a grouping of

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 ...

. It is subdivided into three groups: Archamoeba, Variosea and

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 ...

. In some classifications, the mycetozoan

Myxogastria Myxogastria/Myxogastrea (myxogastrids, ICZN) or Myxomycetes ( ICN) is a class of slime molds that contains 5 orders, 14 families, 62 genera, and 888 species. They are colloquially known as the ''plasmodial'' or ''acellula ...

and Dictyostelia are united in Macromycetozoa (= Eumycetozoa). Conosa includes the species '' Dictyostelium discoideum,'' a social amoeba, and '' Entamoeba histolytica'', a human

pathogen In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a Germ theory of d ...

, among others. Conosa are morphologically defined by a conical microtubular structure, and have been found to be monophyletic.

Characteristics

The Conosa group was first proposed by Thomas Cavalier-Smith in 1998 as a subphylum of

. Cavalier-Smith originally separated this group into two infraphyla: Archamoebae and

. Notable characteristics of these two groups are that Mycetozoa are free living, while Archamoebae are amitochondrial. This clade is morphologically defined by their complex

microtubular Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nanometer, nm and have an inner diameter bet ...

skeleton that forms a partial or complete cone. They have a monolayer of microtubules that surround at least some of the anterior end of the cell and diverge into a cone shape towards the nucleus at the posterior end. This cone of microtubules usually starts at a single

centriole 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 ...

and extends towards the nucleus. They also have a lateral microtubular ribbon towards the cell surface. Conosa can exist as aggregate aerobes with

mitochondria A mitochondrion () is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is us ...

and also as solitary anaerobes with no mitochondria or

peroxisome A peroxisome () is a membrane-bound organelle, a type of microbody, found in the cytoplasm of virtually all eukaryotic cells. Peroxisomes are oxidative organelles. Frequently, molecular oxygen serves as a co-substrate, from which hydrogen perox ...

s. There are mitochondriate and amitochondriate members, as well as free living and parasitic representatives. Mitochondria reduction could be a result of transitions to a parasitic lifestyle, as is seen in the amitochondral human parasite ''Entamoeba histolytica.''

Phylogeny

Conosa are separated from Lobosa, the other Amoebozoa subphylum, by morphological characteristics and genomic differences. Conosa have both amoeboid and

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 ...

forms or stages and more pointed

pseudopodia A pseudopod or pseudopodium (: 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 filaments and ...

with branches. In contrast, Lobosa are entirely amoeboid with broad pseudopodia. Conosa's flagella are artifacts of their ancestral conditions and are seen in trophic and swarm cell phases. Flagellate Conosa have a cone-shaped microtubular skeleton, and non-ciliate forms contain extensive microtubes in the

cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...

, both of which are not seen in Lobosa. While morphological characteristics like pseudopodia and body shape, flagella, and cytoplasm properties have not been regarded as convincing taxonomic suggestions, emerging sequencing data is being used to support Conosa’s monophyly. A study using several hundred phylogenetic markers of 30 species found Conosa to be monophyletic as representatives of Mycetozoa, Entamoebidae, and Pelobionta grouped together using several amino acid sequencing analysis methods. The monophyly of Conosa and the Archamoebea infraphyla was also supported by cDNA sequencing of seventeen Amoebozoans. However, the monophyly of Conosa is not entirely supported. For example, another study using seven protein-coding genes did not find Conosa to be monophyletic due to members of Lobosa sharing a phylogenetic branch with the Conosan lineage Variosea. This same study did find all three Conosan lineages to be monophyletic.

Evolution

The

last common ancestor A most recent common ancestor (MRCA), also known as a last common ancestor (LCA), is the most recent individual from which all organisms of a set are inferred to have descended. The most recent common ancestor of a higher taxon is generally assu ...

of Conosa was likely an aerobic

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 ...

with anterior and recurrent flagellum. It likely had mitochondria, while mitochondrial reduction has resulted in both mitochondriate and amitochondriate members today. The ancestral biflagellate condition is seen in some extant Conosa forms. In some Archamoebae, the posterior flagella and its related cytoskeleton has been lost, and others have lost the entire flagellar system. The conical microtubular skeleton convergently evolved in Archamoebae and Variosea, but not in Mycetozoa. A study of the complete proteomic content of 23 eukaryotic genomes found that representative members of Mycetozoa and Archamoebae do share a common ancestor, and their divergence occurred almost as long ago as the split of

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

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, ...

Gallery

File:Entamoeba histolytica.jpg, '' Entamoeba histolytica'' trophozoite Pelomyxa palustris.jpg, '' Pelomyxa palustris'' File:Badhamia_utricularis_mature.jpg, '' Badhamia utricularis'' (

Physarales Physarales is an order of Amoebozoa in the class Myxomycetes. It contains three families, the Didymiaceae, the Lamprodermataceae, and the Physaraceae. Physarales was circumscribed by Thomas Huston Macbride and published in 1922. Undescr ...

)

References

{{Taxonbar, from=Q1130241 Taxa named by Thomas Cavalier-Smith Amorphea subphyla