Constraints on Phylogenetic Interrelationships among Four Free-living Litostomatean Lineages Inferred from 18S rRNA gene-ITS Region sequences and Secondary Structure of the ITS2 molecule

Ľubomír Rajter,

Peter Vďačný


We investigated interrelationships between four free-living litostomatean lineages, using 18S rRNA gene and ITS region sequences as well as the secondary structure of the ITS2 molecules. Our phylogenetic analyses confirmed the deep split of free-living litostomateans into Rhynchostomatia and Haptoria represented here by Haptorida, Pleurostomatida, and Spathidiida. This bifurcation is also corroborated by the signature of the rhynchostomatian and haptorian ITS2 molecules. Specifically, the consensus stems of helices II and III are longer by one base pair in Rhynchostomatia, while the terminal loops of both helices are longer by one or two nucleotide/-s in Haptoria. A close relationship of Pleurostomatida and Haptorida is favored by quartet likelihood-mapping and supported by a 5’-AG vs. CU-3’ motif in the variable part of helix II and by two morphological apomorphies, i.e., meridionally extending somatic kineties and a non-three-rowed dorsal brush. Although monophyletic origin of Spathidiida is poorly supported in phylogenetic trees, the unique motif 5’-GA vs. UC-3’ present in the consensus helix II stem could be an important molecular synapomorphy of spathidiids, apart from the ancestrally anteriorly curved somatic kineties and the three-rowed dorsal brush. The peculiar family Pseudoholophryidae has very likely found its phylogenetic home among spathidiids, as an early branching lineage.

Słowa kluczowe: dorsal brush, Haptoria, molecular synapomorphies, morphological evolution, Pseudoholophryidae, Rhynchostomatia

Alfaro M. E., Zoller S., Lutzoni F. (2003) Bayes or bootstrap? A simulation study comparing the performance of Bayesian Markov Chain Monte Carlo sampling and bootstrapping in assessing phylogenetic confidence. Mol. Biol. Evol. 20: 255–266

André E. (1915) Recherches sur la faine pélagique du Léman et description de neoveaux genres d’infusoires. Revue Suisse Zool. 22: 179–193

Berger H., Foissner W., Adam H. (1984). Taxonomie, Biometrie und Morphogenese einiger terricoler Ciliaten (Protozoa: Ciliophora). Zool. Jahrb. Syst. 111: 339–367

Bernhart S. H., Hofacker I. L., Will S., Gruber A. R., Stadler P. F. (2008) RNAalifold: improved consensus structure prediction for RNA alignments. BMC Bioinformatics 9: 474

Chang T.-H., Horng J.-T., Huang H.-D. (2008) RNALogo: a new approach to display structural RNA alignment. Nucleic Acids Res. 36: W91–W96

Coleman A. W. (2003) ITS2 is a double-edged tool for eukaryote evolutionary comparisons. Trends Genet. 19: 370–375

Coleman A. W. (2005) Paramecium aurelia revisited. J. Eukaryot. Microbiol. 52: 68–77

Coleman A. W. (2007) Pan-eukaryote ITS2 homologies revealed by RNA secondary structure. Nucleic Acids Res. 35: 3322–3329

Corliss J. O. (1974) The changing world of ciliate systematics: historical analysis of past efforts and a newly proposed phylogenetic scheme of classification for the protistan phylum Ciliophora. Syst. Zool. 23: 91–138

Côté C. A., Greer C. L., Peculis B. A. (2002) Dynamic conformational model for the role of ITS2 in pre-rRNA processing in yeast. RNA 8: 786–797

Ehrenberg C. G. (1838) Die Infusionsthierchen als vollkommene Organismen. Ein Blick in das tiefere organische Leben der Natur. Verlag von Leopold Voss, Leipzig

Fauré-Fremiet E. (1950) Ecologie des ciliés psammophiles littoraux. Bull. Biol. Fr. Belg. 84: 35–75

Ferreira-Cerca S. (2008) Analysis of the in vivo functions and assembly pathway of small subunit ribosomal proteins in Saccharomyces cerevisiae. PhD Thesis, Universität Regensburg. Available at

Foissner W. (1983) Taxonomische Studien über die Ciliaten des Großglocknergebietes (Hohe Tauern, Österreich) I. Familien Holophryidae, Prorodontidae, Plagiocampidae, Colepidae, Enchelyidae und Lacrymariidae nov. fam. Ann. Nat. Hist. Mus. Wien Ser. B Bot. Zool. 84: 49–85

Foissner W. (1984) Infraciliatur, Silberliniensystem und Biometrie einiger neuer und wenig bekannter terrestrischer, limnischer und mariner Ciliaten (Protozoa: Ciliophora) aus den Klassen Kinetofragminophora, Colpodea und Polyhymenophora. Stapfia 12: 1–165

Foissner W. (1987) Neue terrestrische und limnische Ciliaten (Protozoa, Ciliophora) aus Österreich und Deutschland. Sber. Österr. Akad. Wiss., Math.-naturwiss. Kl., Abt. I 195 (year 1986): 217–268

Foissner W. (1996) Ontogenesis in ciliated protozoa, with emphasis on stomatogenesis. In: Ciliates: Cells as Organisms, (Eds. K. Hausmann, B. C. Bradbury). Fischer Verlag, Stuttgart, Jena, New York, 95–177

Foissner W. (1997) Updating the trachelocercids (Ciliophora, Karyorelictea). IV. Transfer of Trachelocerca entzi Kahl, 1927 to the Gymnostomatea as a new genus, Trachelotractus gen. n. (Helicoprorodontidae). Acta Protozool. 36: 63–74

Foissner W. (2016) Terrestrial and semiterrestrial ciliates (Protozoa, Ciliophora) from Venezuela and Galápagos. Denisia 35: 1–912

Foissner W., Al-Rasheid K. (2007) Notes on soil ciliates (Protozoa, Ciliophora) from The Netherlands, with description of Keronopsis schminkei nov. spec. and Apobryophyllum schmidingeri nov. spec. Acta Protozool. 46: 201–220

Foissner W., Foissner I. (1988) The fine structure of Fuscheria terricola Berger et al., 1983 and a proposed new classification of the subclass Haptoria Corliss, 1974 (Ciliophora, Litostomatea). Arch. Protistenkd135: 213–235

Foissner W., Xu K. (2007) Monograph of the Spathidiida (Ciliophora, Haptoria). Vol. I: Protospathidiidae, Arcuospathidiidae, Apertospathulidae. Springer Verlag, Dordrecht

Foissner W., Berger H., Blatterer H., Kohmann F. (1995) Taxonomische und ökologische Revision der Ciliaten des Saprobiensystems – Band IV: Gymnostomatea, Loxodes, Suctoria. Informationsberichte des Bayerischen Landesamtes für Wasserwirtschaft, Deggendorf

Foissner W., Berger H., Schaumburg J. (1999) Identification and ecology of limnetic plankton ciliates. Informationsberichte des Bayerischen Landesamtes für Wasserwirtschaft, Deggendorf

Foissner W., Agatha S., Berger H. (2002) Soil ciliates (Protozoa, Ciliophora) from Namibia (Southwest Africa) with emphasis on two contrasting environments, the Etosha region and the Namib Desert. Denisia 5: 11459

Gabilondo R., Foissner W. (2009) Four new fuscheriid soil ciliates (Ciliophora: Haptorida) from four biogeographic regions. Acta Protozool. 48: 1–24

Gao F., Warren A., Zhang Q., Gong J., Miao M., Sun P., Xu D., Huang J., Yi Z., Song W. (2016) The all-data-based evolutionary hypothesis of ciliated protists with a revised classification of the phylum Ciliophora (Eukaryota, Alveolata). Sci. Rep. 6: 24874

Gao S., Song W., Ma H., Clamp J. C., Yi Z., Al-Rasheid K. A. S., Chen Z., Lin X. (2008) Phylogeny of six genera of the subclass Haptoria (Ciliophora, Litostomatea) inferred from sequences of the gene coding for small subunit ribosomal RNA. J. Eukaryot. Microbiol. 55: 562–566

Gentekaki E., Kolisko M., Boscaro V., Bright K. J., Dini F., Di Giuseppe G., Gong Y., Miceli C., Modeo L., Molestina R. E., Petroni G., Pucciarelli S., Roger A. J., Strom S. L., Lynn D. H. (2014) Large-scale phylogenomic analysis reveals the phylogenetic position of the problematic taxon Protocruzia and unravels the deep phylogenetic affinities of the ciliate lineages. Mol. Phylogenet. Evol. 78: 36–42

Gentekaki E., Kolisko M., Gong Y., Lynn D. (2017) Phylogenomics solves a long-standing evolutionary puzzle in the ciliate world: the subclass Peritrichia is monophyletic. Mol. Phylogenet. Evol. 106: 1–5

Gruber A. R., Lorenz R., Bernhart S. H., Neuböck R., Hofacker I. L. (2008) The Vienna RNA Websuite. Nucleic Acids Res. 36 (Suppl. 2): W70–W74

Guindon S., Gascuel O. (2003) A simple, fast, and accurate algorithm to estimate large phylogenies by maximum likelihood. Syst. Biol. 52: 696‒704

Guindon S., Dufayard J. F., Lefort V., Anisimova M., Hordijk W., Gascuel O. (2010) New algorithms and methods to estimate maximum-likelihood phylogenies: assessing the performance of PhyML 3.0. Syst. Biol. 59: 307‒321

Hall T. A. (1999) BioEdit: a user-friendly biological sequence alignment editor and analysis program for Windows 95/98/NT. Nucleic Acids Symp. Ser. 41: 95–98

Hillis D. M., Bull J. J. (1993) An empirical test of bootstrapping as a method for assessing confidence in phylogenetic analysis. Syst. Biol. 42: 182–192

Huson D. H. (1998) SplitsTree: analyzing and visualizing evolutionary data. Bioinformatics 14: 68–73

Huson D. H., Dezulian T., Kloepper T., Steel M. A. (2004) Phylogenetic super-networks from partial trees. Trans. Comp. Biol. Bioinform. 1: 151–158

Jang S. W., Vďačný P., Shazib S. U. A., Shin M. K. (2014) Morphological and molecular characterization of the name-bearing type species Rimaleptus binucleatus (Kahl, 1931), with a phylogenetic re-analysis of dileptid evolutionary history (Ciliophora: Litostomatea: Rhynchostomatia). Eur. J. Protistol. 50: 456–471

Jang S. W., Vďačný P., Shazib S. U. A., Shin M. K. (2015) Morphology, ciliary pattern and molecular phylogeny of Trachelophyllum brachypharynx Levander, 1894 (Litostomatea, Haptoria, Spathidiida). Acta Protozool. 54: 123–135

Jang S. W., Vďačný P., Shazib S. U. A., Shin M. K. (2017) Linking morphology and molecules: integrative taxonomy of spathidiids (Protista: Ciliophora: Litostomatea) from Korea. J. Nat. Hist. 51: 939–974

Jankowski A. W. [Ânkovskij A. V.] (1978) Novye vysšie taksony resničnyh prostejših (Ciliophora) [New higher taxa of ciliated protozoa (Ciliophora)]. In: Morfologiâ, sistematika i èvolûciâ životnyh. Sbornik naučnyh rabot [Morphology, systematics and evolution of animals. Set of scientific papers], (Ed. L. Â. Borkin [L. Ya. Borkin]). Akademiâ Nauk SSSR, Zool. Inst., Leningrad: 88–90 (in Russian)

Jankowski A. W. [Ânkovskij A. V.] (1980) Konspekt novoj sistemy tipa Ciliophora [Conspectus of a new system of the phylum Ciliophora]. Trudy Zool. Inst. Leningrad 94: 103–121 (in Russian)

Johnson M. D., Tengs T., Oldach D. W., Delwiche C. F., Stoecker D. K. (2004) Highly divergent SSU rRNA genes found in the marine ciliates Myrionecta rubra and Mesodinium pulexProtist 155: 347–359

Kahl A. (1930a) Neue und ergänzende Beobachtungen holotricher Infusorien II. Arch. Protistenkd. 70: 313–416

Kahl A. (1930b) Urtiere oder Protozoa I: Wimpertiere oder Ciliata (Infusoria) 1. Allgemeiner Teil und Prostomata. Tierwelt Dtl. 18: 1–180

Kahl A. (1931) Urtiere oder Protozoa I: Wimpertiere oder Ciliata (Infusoria) 2. Holotricha außer den im 1. Teil behandelten Prostomata. Tierwelt Dtl. 21: 181–398

Kreutz M., Foissner W. (2006) The Sphagnum ponds of Simmelried in Germany: a biodiversity hot-spot for microscopic organisms. Protozool. Monogr. 3: 1–267

Kwon C. B., Vďačný P., Shazib S. U. A., Shin M. K. (2014) Morphology and molecular phylogeny of a new haptorian ciliate, Chaenea mirabilis sp. n., with implications for the evolution of the dorsal brush in haptorians (Ciliophora, Litostomatea). J. Eukaryot. Microbiol. 61: 278–292

Li J., Liu W., Gao S., Warren A., Song W. (2013) Multigene-based analyses of the phylogenetic evolution of oligotrich ciliates, with consideration of the internal transcribed spacer 2 secondary structure of three systematically ambiguous genera. Eukaryot. Cell 12: 430–437

Li J., Zhan Z., Xu K. (2017) Systematics and molecular phylogeny of the ciliate genus Pseudokeronopsis (Ciliophora, Hypotrichia). J. Eukaryot. Microbiol. 64: 850–872

Lin X., Song W., Li J. (2007) Description of two new marine pleurostomatid ciliates, Loxophyllum choii nov. spec. and L. shini nov. spec. (Ciliophora, Pleurostomatida) from China. Eur. J. Protistol. 43: 131‒139

Lin X., Al-Rasheid K. A. S., Al-Quaraishy S. A., Al-Farraj S. A., Song W. (2008) Identification of three highly confused marine Loxophyllum (Ciliophora: Pleurostomatida) with a key to seven congeners from the China Sea. J. Eukaryot. Microbiol. 55: 331‒342

Lin X., Warren A., Song W. (2009) Pleurostomatids. In: Free-living Ciliates in the Bohai and Yellow Seas, China (Eds. W. Song, A. Warren, X. Hu). Science Press, Beijing, 93–134

Lipscomb D. L., Riordan G. P. (1990) The ultrastructure of Chaenea teres and an analysis of phylogeny of the haptorid ciliates. J. Protozool. 37: 287–330

Lynn D. H. (2008) The Ciliated Protozoa. Characterization, Classification and Guide to the literature. 3rd ed. Springer, Dordrecht

Medlin L., Elwood H. J., Stickel S., Sogin M. L. (1988) The characterization of enzymatically amplified eukaryotic 16S-like rRNA-coding regions. Gene 71: 491–499

Miao M., Warren A., Song W., Wang S., Shang H., Chen Z. (2008) Analysis of the internal transcribed spacer 2 (ITS2) region of scuticociliates and related taxa (Ciliophora, Oligohymenophorea) to infer their evolution and phylogeny. Protist 159: 519–533

Miller M. A., Pfeiffer W., Schwartz T. (2010) Creating the CIPRES Science Gateway for inference of large phylogenetic trees. In: Proceedings of the Gateway Computing Environments Workshop (GCE). New Orleans, LA, 1–8

Pan H., Gao F., Li J., Lin X., Al-Farraj S. A., Al-Rasheid K. A. S. (2010) Morphology and phylogeny of two new pleurostomatid ciliates, Epiphyllum shenzhenense n. sp. and Loxophyllum spirellum n. sp. (Protozoa, Ciliophora) from a mangrove wetland, South China. J. Eukaryot. Microbiol. 57: 421428

Pan H., Gao F., Lin X., Warren A., Song W. (2013) Three new Loxophyllum species (Ciliophora: Pleurostomatida) from China with a brief review of the marine and brackish Loxophyllum species. J. Eukaryot. Microbiol. 60: 44–56

Pawlowski J. (2000) Introduction to the molecular systematics of foraminifera. Micropaleontology 46 (Suppl. 1): 1–12

Ponce-Gordo F., Fonseca-Salamanca F., Martínez-Díaz R. A. (2011) Genetic heterogeneity in internal transcribed spacer genes of Balantidium coli (Litostomatea, Ciliophora). Protist 162: 774–794

Posada D. (2008) JModelTest: phylogenetic model averaging. Mol. Biol. Evol. 25: 1253–1256

Quennerstedt A. (1867) Bidrag till sveriges infusorie-fauna. II. Acta Univ. Lund. 4: 1–48

Rajter Ľ., Vďačný P. (2016) Rapid radiation, gradual extinction and parallel evolution challenge generic classification of spathidiid ciliates (Protista, Ciliophora). Zool. Scr. 45: 200–223

Schewiakoff W. [Ševâkov V.] (1896) Organizacia i sistematika infusoria Aspirotricha (Holotricha auctorum) [The organization and systematics of the infusoria Aspirotricha (Holotricha auctorum)]. Zap. Imp. Akad. Nauk (8e Série) 4: 1–395 (in Russian)

Schmidt H. A., Strimmer K., Vingron M., von Haeseler A. (2002) TREE-PUZZLE: maximum likelihood phylogenetic analysis using quartets and parallel computing. Bioinformatics 18: 502–504

Schultz J., Maisel S., Gerlach D., Müller T., Wolf M. (2005) A common core of secondary structure of the internal transcribed spacer 2 (ITS2) throughout the Eukaryota. RNA 11: 361–364

Sela I., Ashkenazy H., Katoh K., Pupko T. (2015) GUIDANCE2: accurate detection of unreliable alignment regions accounting for the uncertainty of multiple parameters. Nucleic Acids Res. 43: 7–14

Shazib S. U. A., Vďačný P., Kim J. H., Jang S. W., Shin M. K. (2016) Molecular phylogeny and species delimitation within the ciliate genus Spirostomum (Ciliophora, Postciliodesmatophora, Heterotrichea), using the internal transcribed spacer region. Mol. Phylogenet. Evol. 102: 128–144

Small E. B., Lynn D. H. (1981) A new macrosystem for the Phylum Ciliophora Doflein, 1901. BioSystems 14: 387–401

Stein F. (1863) Auf der Reise in die Ostsee bei Wismar beobachtete neue oder noch nicht genügend bekannte Infusorienformen. Amtl. Ber. Ver. Dt. Naturf. Ärzte Karlsbad 37: 161–162, 165–166

Stokes A. C. (1890) Notices of new fresh-water infusoria. Proc. Am. Phil. Soc. 28: 74–80

Strimmer K., von Haeseler A. (1997) Likelihood-mapping: a simple method to visualize phylogenetic content of a sequence alignment. Proc. Natl. Acad. Sci. USA 94: 6815–6819

Strüder-Kypke M. C., Wright A.-D. G., Foissner W., Chatzinotas A., Lynn D. H. (2006) Molecular phylogeny of litostome ciliates (Ciliophora, Litostomatea) with emphasis on free-living haptorian genera. Protist 157: 261278

Sun P., Clamp J. C., Xu D. (2010) Analysis of the secondary structure of ITS transcripts in peritrich ciliates (Ciliophora, Oligohymenophorea): implications for structural evolution and phylogenetic reconstruction. Mol. Phylogenet. Evol. 56: 242–251

Sun P., Clamp J. C., Xu D., Huang B., Shin M. K., Turner F. (2013) An ITS-based phylogenetic framework for the genus Vorticella : finding the molecular and morphological gaps in a taxonomically difficult group. Proc. R. Soc. B 280: 20131177

van Nues R. W., Rientjes J. M., van der Sande C. A., Zerp S. F., Sluiter C., Venema J., Planta R. J., Raué H. A. (1994) Separate structural elements within internal transcribed spacer 1 of Saccharomyces cerevisiae precursor ribosomal RNA direct the formation of 17S and 26S rRNA. Nucleic Acids Res. 22: 912–919

Vďačný P. (2017) Integrative taxonomy of ciliates: Assessment of molecular phylogenetic content and morphological homology testing. Eur. J. Protistol. 61: 388–398

Vďačný P., Foissner W. (2009) Ontogenesis of Dileptus terrenus and Pseudomonilicaryon brachyproboscis (Ciliophora, Haptoria). J. Eukaryot. Microbiol. 56: 232–243

Vďačný P., Foissner W. (2012) Monograph of the dileptids (Protista, Ciliophora, Rhynchostomatia). Denisia 31: 1–529

Vďačný P., Foissner W. (2013) Synergistic effects of combining morphological and molecular data in resolving the phylogenetic position of Semispathidium (Ciliophora, Haptoria), with description of S. breviarmatum sp. n. from tropical Africa. Zool. Scr. 42: 529–549

Vďačný P., Rajter Ľ. (2015) Reconciling morphological and molecular classification of predatory ciliates: evolutionary taxonomy of dileptids (Ciliophora, Litostomatea, Rhynchostomatia). Mol. Phylogenet. Evol. 90: 112–128

Vďačný P., Rataj M. (2017) Evaluation of systematic position of helicoprorodontids and chaeneids (Ciliophora, Litostomatea): an attempt to break long branches in 18S rRNA gene phylogenies. J. Eukaryot. Microbiol. 64: 608–621

Vďačný P., Orsi W., Foissner W. (2010) Molecular and morphological evidence for a sister group relationship of the classes Armophorea and Litostomatea (Ciliophora, Intramacronucleata, Lamellicorticata infraphyl. nov.), with an account on basal haptorid litostomateans. Eur. J. Protistol. 46: 298–309

Vďačný P., Bourland W. A., Orsi W., Epstein S. S., Foissner W. (2011a) Phylogeny and classification of the Litostomatea (Protista, Ciliophora), with emphasis on free-living taxa and the 18S rRNA gene. Mol. Phylogenet. Evol. 59: 510‒522

Vďačný P., Orsi W., Bourland W. A., Shimano S., Epstein S. S., Foissner W. (2011b) Morphological and molecular phylogeny of dileptids: resolution at the base of the class Litostomatea (Ciliophora, Intramacronucleata)Eur. J. Protistol. 47: 295313

Vďačný P., Bourland W. A., Orsi W., Epstein S. S., Foissner W. (2012) Genealogical analyses of multiple loci of litostomatean ciliates (Protista, Ciliophora, Litostomatea). Mol. Phylogenet. Evol. 65: 397‒411

Vďačný P., Breiner H.-W., Yashchenko V., Dunthorn M., Stoeck T., Foissner W. (2014) The chaos prevails: molecular phylogeny of the Haptoria (Ciliophora, Litostomatea). Protist 165: 93‒111

Vďačný P., Rajter Ľ., Shazib S. U. A, Jang S. W., Kim J. H., Shin M. K. (2015) Reconstruction of evolutionary history of pleurostomatid ciliates (Ciliophora, Litostomatea, Haptoria): interplay of morphology and molecules. Acta Protozool. 54: 9–29

Vďačný P., Rajter Ľ., Shazib S. U. A, Jang S. W., Shin M. K. (2017) Diversification dynamics of rhynchostomatian ciliates: the impact of seven intrinsic traits on speciation and extinction in a microbial group. Sci. Rep. 7: 9918

Weisse T., Strüder-Kypke M. C., Berger H., Foissner W. (2008) Genetic, morphological, and ecological diversity of spatially separated clones of Meseres corlissi Petz & Foissner, 1992 (Ciliophora, Spirotrichea). J. Eukaryot. Microbiol. 55: 257–270

Wolf M., Achtziger M. C., Schultz J., Dandekar T., Müller T. (2005) Homology modeling revealed more than 20,000 rRNA internal transcribed spacer 2 (ITS2) secondary structures. RNA 11: 1616–1623

Wu L., Clamp J. C., Yi Z., Li J., Lin X. (2015) Phylogenetic and taxonomic revision of an enigmatic group of haptorian ciliates, with establishment of the Kentrophyllidae fam. n. (Protozoa, Ciliophora, Litostomatea, Pleurostomatida). PLoS One 10: e0123720

Wu L., Jiao X., Shen Z., Yi Z., Li J., Warren A., Lin X. (2016) New taxa refresh the phylogeny and classification of pleurostomatid ciliates (Ciliophora, Litostomatea). Zool. Scr. 46: 245–253

Yi Z., Chen Z., Warren A., Roberts D., Al-Rasheid K. A. S., Miao M., Gao S., Shao C., Song W. (2008) Molecular phylogeny of Pseudokeronopsis (Protozoa, Ciliophora, Urostylida), with reconsideration of three closely related species at inter- and intra-specific levels inferred from the small subunit ribosomal RNA gene and the ITS1-5.8S-ITS2 region sequences. J. Zool. 275: 268–275

Zhang Q., Simpson A., Song W. (2012) Insights into the phylogeny of systematically controversial haptorian ciliates (Ciliophora, Litostomatea) based on multigene analyses. Proc. R. Soc. Lond. B Biol. Sci. 279: 2625–2635

Zuker M. (2003) Mfold web server for nucleic acid folding and hybridization prediction. Nucleic Acids Res. 31: 3406–3415

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