Theapusomonads (familyApusomonadidae) are a group ofprotozoanzooflagellates that glide on surfaces, and mostly consumeprokaryotes. They are of particular evolutionary interest because they appear to be the sister group to theOpisthokonts, the clade that includes bothanimals andfungi. Together with theBreviatea, these form theObazoa clade.[3][4][5]
Apusomonads are smallglidingheterotrophicbiflagellates (i.e. with twoflagella) that possess aproboscis, formed partly or entirely by the anterior flagellum surrounded by a membranous sleeve. There is apellicle 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:[6]
"Amastigomonas-like" cell plan, with an oval or oblong cell that generally formspseudopodia 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 withApusomonas. Organisms with this body plan, although historically assigned to the same genusAmastigomonas, are aparaphyletic group from whichApusomonas has evolved.[6][7]
The apusomonads are the sister group toOpisthokonta, the lineage that includesanimals,fungi and an array of relatedprotists. Because of this, apusomonads occupy an importantphylogenetic position to understandeukaryotic evolution. They retain ancestral characteristics, such as thebiflagellatebody plan, which in opisthokonts evolves into a uniflagellate plan.[7]
Apusomonads are vital to understandingmulticellularity. Genes involved in multicellularity have been found in the apusomonadThecamonas,[8] such as adhesion proteins, calcium-signaling genes and types of sodium channels characteristic of animals.[6] Thegenome of the strain "Amastigomonas sp." presents theintegrin-mediatedadhesion machinery, the primarycell-matrix adhesion mechanism seen inMetazoa (animals).[9]
^abCavalier-Smith, Thomas (May 2013). "Early evolution of eukaryote feeding modes, cell structural diversity, and classification of the protozoan phyla Loukozoa, Sulcozoa, and Choanozoa".European Journal of Protistology.49 (2): 115–178 Document online.doi:10.1016/j.ejop.2012.06.001.ISSN0932-4739.PMID23085100.
^abCavalier-Smith, Thomas; Chao, Ema E. (October 2010). "Phylogeny and evolution of Apusomonadida (Protozoa: Apusozoa): new genera and species".Protist.161 (4):549–576.doi:10.1016/j.protis.2010.04.002.PMID20537943.
^abcdeHeiss AA, Lee WJ, Ishida KI, Simpson AG (2015). "Cultivation and Characterisation of New Species of Apusomonads (the Sister Group to Opisthokonts), Including Close Relatives ofThecamonas (Chelonemonas n. gen.)".Journal of Eukaryotic Microbiology.62 (5):637–649.doi:10.1111/jeu.12220.PMID25912654.
^abcdefTorruella G, Galindo LJ, Moreira D, Ciobanu M, Heiss AA, Yubuki N, et al. (November 2022). "Expanding the molecular and morphological diversity of Apusomonadida, a deep-branching group of gliding bacterivorous protists".Journal of Eukaryotic Microbiology.70 (2) e12956.doi:10.1111/jeu.12956.hdl:2117/404026.
^Adl SM, Bass D, Lane CE, Lukeš J, Schoch CL, Smirnov A, Agatha S, Berney C, Brown MW, Burki F, Cárdenas P, Čepička I, Chistyakova L, del Campo J, Dunthorn M, Edvardsen B, Eglit Y, Guillou L, Hampl V, Heiss AA, Hoppenrath M, James TY, Karnkowska A, Karpov S, Kim E, Kolisko M, Kudryavtsev A, Lahr DJG, Lara E, Le Gall L, Lynn DH, Mann DG, Massana R, Mitchell EAD, Morrow C, Park JS, Pawlowski JW, Powell MJ, Richter DJ, Rueckert S, Shadwick L, Shimano S, Spiegel FW, Torruella G, Youssef N, Zlatogursky V, Zhang Q (2019)."Revisions to the Classification, Nomenclature, and Diversity of Eukaryotes".Journal of Eukaryotic Microbiology.66 (1):4–119.doi:10.1111/jeu.12691.PMC6492006.PMID30257078.
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