Apusomonadida

The apusomonads (order 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 includes both animals and fungi. Together with the Breviatea, these form the Obazoa clade. Apusomonads are small gliding heterotrophic biflagellates (= with two flagella) that possess a proboscis, formed partly or entirely by the anterior flagellum surrounded by a membranous sleeve. There is a pellicle under the dorsal cell membrane that extends into the proboscis sleeve and into a skirt that covers the sides of the cell. Apusomonads present two different cell plans: Derived cell plan, represented by Apusomonas, with a round cell body and a mastigophore, a projection of the cell containing both basal bodies at its end. "Amastigomonas-like" cell plan, with an oval or oblong cell that generally forms pseudopodia from the ventral surface, with no mastigophore, and the proboscis comprising solely the flagellum and the sleeve. These characteristics are considered 'primitive' or 'ancestral' in comparison with Apusomonas. Organisms with this body plan, although historically assigned to the same genus Amastigomonas, are a paraphyletic group from which Apusomonas has evolved. The apusomonads are the sister group to Opisthokonta, the lineage that includes animals, fungi and an array of related protists. Because of this, apusomonads occupy an important phylogenetic position to understand eukaryotic evolution. They retain ancestral characteristics, such as the biflagellate body plan, which in opisthokonts evolves into a uniflagellate plan. Apusomonads are vital to understanding multicellularity. Genes involved in multicellularity have been found in the apusomonad Thecamonas, such as adhesion proteins, calcium-signaling genes and types of sodium channels characteristic of animals. The genome of the strain "Amastigomonas sp.

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Related concepts (14)

Eukaryote

The eukaryotes constitute the domain of Eukaryota (juːˈkærioʊts,_-əts), organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms are eukaryotes. They constitute a major group of life forms, alongside the two groups of prokaryotes, the Bacteria and the Archaea. Eukaryotes represent a small minority of the number of organisms, but due to their generally much larger size, their collective global biomass is much larger than that of prokaryotes.

Holozoa

Holozoa is a group of organisms that includes animals and their closest single-celled (protist) relatives, but excludes fungi and all other organisms. It is a monophyletic group or clade, a lineage consisting of all descendants of a common ancestor. Among these descendants, the protists are of high interest because of their close relationship to animals: in the search for the genes responsible for animal multicellularity within these protists, they help elucidate the nature of the unicellular ancestor of animals.

Apusomonadida