Opalinata is a diverse assemblage of modified parasitic protists known as 'opalines'. They inhabit the intestines of various animals, primarily amphibians. They are found on every continent. Among them, the opalinids are highly unusual protists: their large cells have numerous flagella and from two to hundreds of nuclei. Their cell surface is delicately folded, giving it an iridescent appearance (hence their name, a reference to the iridescent opal). Another important group of opalines is Blastocystis, a prevalent parasite of humans and other animals.[5]
Bicosoecida is a small group that contains free-living marine and freshwaternanoflagellates that feed on bacteria. They are present in every ecosystem, including extreme environments such as the deep sea or salt flats. They play a crucial role in the microbial food web by composing the link between bacteria and higher trophic levels. They are also important in biogeochemical cycles by remineralizing the nutrients. Their classification has changed multiple times over the years,[6] and is still an unresolved issue.[7]
All of Bigyra are heterotrophic microorganisms evolved from the last common ancestor of Stramenopiles, which is thought to have been phototrophic. Following this hypothesis, the bigyran ancestor would have secondarily lost their photosynthetic plastids. Some characteristics of bigyran groups can be explained by their origin from ancestral plastids. For example, labyrinthulomycetes can produce omega-3 poly-unsaturated fatty acids through a desaturase usually present in chloroplasts.[9]
The monophyly of Bigyra remains uncertain. The positions of the two bigyran clades (Opalozoa and Sagenista) are not consistent between the published studies, because they diverged from each other very early after the separation from the ancestor of all stramenopiles. This 'deep branching' makes it difficult to find the exact branching order of bigyran clades.[2] Additionally, not all clades are well-represented by molecular data in these studies.[10] Several studies support the monophyly of Bigyra.[10][11] Other studies support its paraphyly.[12][13]
Bigyra was first described in 1997 by the protozoologistThomas Cavalier-Smith as a phylum within Heterokonta (synonym of Stramenopiles). Bigyra was defined as organisms with the synapomorphy of a ciliary transition region (i.e. a structure that controls protein transport at the base of the flagellum) with structures in the shape of two helices or rings, hence the name 'bigyra' meaning 'double helix'. It contained three subgroups:[1]
Posterior analyses completely changed the phylogeny of Stramenopiles. They revealed Pseudofungi and Bigyromonadea were more closely related to a monophyletic Ochrophyta than they were to Opalinata, meaning that the synapomorphy of a double helix could have been present in the common ancestor of all heterokonts. This rendered Bigyra paraphyletic. Consequently, Bigyra was revised and modified in 2006 to comprise a different set of three subphyla:
^ abcAdl 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.
^ abcBennett, Reuel M.; Honda, D.; Beakes, Gordon W.; Thines, Marco (2017). "Chapter 14. Labyrinthulomycota". In Archibald, John M.; Simpson, Alastair G.B.; Slamovits, Claudio H. (eds.). Handbook of the Protists. Springer. pp. 507–542. doi:10.1007/978-3-319-28149-0_25. ISBN978-3-319-28147-6.
^Karpov SA, Sogin ML, Silberman JD (2001). "Rootlet homology, taxonomy, and phylogeny of bicosoecids based on 18S rRNA gene sequences". Protistology. 2 (1): 34–47.
^Schoenle A, Hohlfeld M, Rybarski A, Sachs M, Freches E, Wiechmann K, Nitsche F, Arndt H (2022). "Cafeteria in extreme environments: Investigations on C. burkhardae and three new species from the Atacama Desert and the deep ocean". European Journal of Protistology. 85: 125905. doi:10.1016/j.ejop.2022.125905. PMID35868212. S2CID249935619.
^Tsui, Clement K M; Marshall, Wyth; Yokoyama, Rinka; Honda, Daiske; Lippmeier, J Casey; Craven, Kelly D; Peterson, Paul D; Berbee, Mary L (January 2009). "Labyrinthulomycetes phylogeny and its implications for the evolutionary loss of chloroplasts and gain of ectoplasmic gliding". Molecular Phylogenetics and Evolution. 50 (1): 129–40. doi:10.1016/j.ympev.2008.09.027. PMID18977305.
^ abCavalier-Smith T (1998). "Sagenista and Bigyra, two phyla of heterotrophic heterokont chromists". Archiv für Protistenkunde. 148 (3): 253–267. doi:10.1016/S0003-9365(97)80006-1.