Armophorea is a class ofciliates in the subphylumIntramacronucleata.[1][2].[3] It was first resolved in 2004[4] and comprises three orders: Metopida, Clevelandellida,[5] and Armophorida.[6] Previously members of this class were thought to beheterotrichs because of similarities in morphology, most notably a characteristic dense arrangement ofcilia surrounding their oral structures.[7] However, the development ofgenetic tools and subsequent incorporation of DNA sequence information has led to major revisions in the evolutionary relationships of manyprotists, including ciliates.[8] Metopids, clevelandellids, and armophorids were grouped into this class based on similarities in theirsmall subunit rRNA sequences, making them one of two so-called "riboclasses" of ciliates, however, recent analyses suggest that Armophorida may not be related to the other two orders.[9]
The name Armophorea is thought to be derived from the Latin wordarma, meaning weapons, orarmus, meaning shoulder. This name refers to the caenomorphid members of this class, which have a characteristic military helmet-like morphology, and also a twisted appearance that looks like a shoulder.[7]
Free-living armophoreans live inanoxic or microaerobic habitats, in the sediment or water column where there is reduced or absent oxygen. Thus their distribution is quite limited, although they are found globally in both marine and freshwater habitats, as well as in terrestrial sediment. Clevelandellids live ascommensal symbionts inside of the digestive tracts of terrestrial and aquatic animals.[7]
Armophoreans can survive byencystment when in unfavorable environmental conditions. This is quite important for clevelandellids because it facilitates their transmission between hosts.[7]
Like most anaerobic ciliates, armophoreans have mitochondria-derived organelles calledhydrogenosomes. These specialized organelles produce energy for the cell in absence of oxygen by thefermentation of pyruvate into acetate and hydrogen. Armophoreans harbormethanogenicendosymbioticarchaea that have been located in the cytoplasm adjacent to their hydrogenosomes. Host cells can contain up to 10,000 methanogens, and they are thought to play roles in host growth and metabolism.[10] It is hypothesized that these symbionts consume the hydrogen that is produced as an end-product of fermentation, making it a more favorable reaction and increasing its energetic yield.[11] Marine armophoreans also harbor ectosymbiotic bacteria that aresulfate reducers, which are thought to play a similar role as the endosymbiotic methanogens in that they also consume hydrogen as a metabolite of host fermentation.[10]
Methanogenesis by these endosymbiotic archaea can contribute substantially to the production of methane in sulfate-rich, anoxic detrital sediments and the anoxic water column, but the contribution is modest (>2%) in sandy sediments where the ciliates are lower in number.[12] This is in contrast to clevelandellids: over 80% of the methane produced by the American cockroach can be attributed to these ciliates via their methanogenic endosymbionts.[7]
^AFFA'A, FELIX-MARIE; HICKEY, DONAL A.; STRUDER-KYPKE, MICHAELA; LYNN, DENIS H. (May 2004). "Phylogenetic Position of Species in the Genera Anoplophrya, Plagiotoma, and Nyctotheroides (Phylum Ciliophora), Endosymbiotic Ciliates of Annelids and Anurans".The Journal of Eukaryotic Microbiology.51 (3):301–306.doi:10.1111/j.1550-7408.2004.tb00570.x.ISSN1066-5234.PMID15218698.S2CID34941205.
^De Puytorac, P; Grain, J (1976). "Ultrastructure du cortex buccal et évolution chez les ciliés".Protistologica.12:49–67.
^Jankowski, AW (1964). "Morphology and evolution of Ciliophora. III. Diagnoses and phylogenesis of 53 sapropelobionts, mainly of the order Heterotrichida".Protist.107:185–294.
^abcdeLynn, Denis H. (2008).The Ciliated Protozoa: Characterization, Classification, and Guide to the Literature. Springer Science + Business Media B.V.ISBN978-1-4020-8239-9.OCLC758317642.
^Li, Song; Bourland, William A.; Al-Farraj, Saleh A.; Li, Lifang; Hu, Xiaozhong (October 2017). "Description of two species of caenomorphid ciliates (Ciliophora, Armophorea): Morphology and molecular phylogeny".European Journal of Protistology.61 (Pt A):29–40.doi:10.1016/j.ejop.2017.08.001.PMID28843744.
^abFenchel, Tom; Finlay, Bland J. (2010), "Free-Living Protozoa with Endosymbiotic Methanogens",(Endo)symbiotic Methanogenic Archaea, Springer Berlin Heidelberg, pp. 1–11,doi:10.1007/978-3-642-13615-3_1,ISBN978-3-642-13614-6
^Worm, Petra; Müller, Nicolai; Plugge, Caroline M.; Stams, Alfons J. M.; Schink, Bernhard (2010), "Syntrophy in Methanogenic Degradation",(Endo)symbiotic Methanogenic Archaea, Springer Berlin Heidelberg, pp. 143–173,doi:10.1007/978-3-642-13615-3_9,ISBN978-3-642-13614-6
^Fenchel, T. (January 1993). "Methanogenesis in marine shallow water sediments: The quantitative role of anaerobic protozoa with endosymbiotic methanogenic bacteria".Ophelia.37 (1):67–82.doi:10.1080/00785326.1993.10430378.ISSN0078-5326.
^abLukáš Pecina; Peter Vďačný (2022). "DNA barcoding and coalescent-based delimitation of endosymbiotic clevelandellid ciliates (Ciliophora: Clevelandellida): a shift to molecular taxonomy in the inventory of ciliate diversity in panesthiine cockroaches".Zoological Journal of the Linnean Society.194 (4):1072–1102.doi:10.1093/zoolinnean/zlab063.
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Data related toArmophorea at Wikispecies