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      Morphological and molecular description of Rhadinorhynchus laterospinosus Amin, Heckmann & Ha, 2011 (Acanthocephala, Rhadinorhynchidae) from marine fish off the Pacific coast of Vietnam Translated title: Description morphologique et moléculaire de Rhadinorhynchus laterospinosus Amin, Heckmann & Ha, 2011 (Acanthocephala, Rhadinorhynchidae) des poissons marins du large de la côte pacifique du Vietnam

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          Rhadinorhynchus laterospinosus Amin, Heckmann & Ha, 2011 (Rhadinorhynchidae) was described from a single female collected from a trigger fish, Balistes sp. (Balistidae) from the northern Pacific coast of Vietnam in Halong Bay, Gulf of Tonkin. More recent collections of fishes in 2016 and 2017 revealed wider host and geographical distributions. We report this Acanthocephala from nine species of fish representing six families (including the original record from Balistes sp.) along the whole Pacific coast of Vietnam. The fish species are Alectis ciliaris (Carangidae), Auxis rochei (Scombridae), Auxis thazard (Scombridae), Leiognathus equulus (Leiognathidae), Lutjanus bitaeniatus (Lutjanidae), Megalaspis cordyla (Carangidae), Nuchequula flavaxilla (Leiognathidae), and Tylosurus sp. (Belonidae). We provide a complete description of males and females of R. laterospinosus, discuss its hook metal microanalysis using EDAX, and its micropores. Specimens of this species characteristically have lateral trunk spines bridging the anterior ring of spines with posterior field of ventral spines and a proboscis with 15–19 longitudinal alternating rows of 21–26 hooks each varying with host species. We demonstrate the effect of host species on the distribution and size of the trunk, proboscis, proboscis hooks, trunk spines, and reproductive structures. The molecular profile of this acanthocephalan, based on 18S rDNA and cox1 genes, groups with other Rhadinorhynchus species and further seems to confirm the paraphyly of the genus, which is discussed.

          Translated abstract

          Rhadinorhynchus laterospinosus Amin, Heckmann & Ha, 2011 (Rhadinorhynchidae) a été décrit d’une seule femelle prélevée chez Balistes sp. (Balistidae) sur la côte nord du Pacifique du Vietnam, dans la Baie d’Along, golfe du Tonkin. Des collections de poissons plus récentes, en 2016 et 2017, ont révélé une répartition en hôtes et en localités géographiques plus étendue. Nous rapportons cet Acanthocéphale de 9 espèces de poissons représentant 6 familles (y compris la mention originale chez Balistes sp.), le long de la côte pacifique du Vietnam. Les espèces de poissons sont Alectis ciliaris (Carangidae), Auxis rochei (Scombridae), Auxis thazard (Scombridae), Leiognathus equulus (Leiognathidae), Lutjanus bitaeniatus (Lutjanidae), Megalaspis cordyla (Carangidae), Nuchequula flavaxilla (Leiognathidae) et Tylosurus sp. (Belonidae). Nous fournissons une description complète des mâles et des femelles de R. laterospinosus, de la microanalyse des métaux des crochets à l’aide d’EDAX, et de ses micropores. Les spécimens de cette espèce ont généralement des épines latérales du tronc reliant l’anneau antérieur d’épines avec un champ postérieur d’épines ventrales et un proboscis avec 15–19 rangées longitudinales alternées de 21 à 26 crochets, variant avec l’espèce hôte. Nous démontrons l’effet des espèces hôtes sur la distribution et la taille du tronc, du proboscis, des crochets du proboscis, des épines du tronc et des structures de reproduction. Le profil moléculaire de cet acanthocéphale, basé sur les gènes de l’ADNr 18S et de cox1, forme un groupe avec d’autres espèces de Rhadinorhynchus et semble en outre confirmer la paraphylie du genre, ce qui est discuté.

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          Most cited references 37

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          Classification of the acanthocephala.

           O Amin (2013)
          In 1985, Amin presented a new system for the classification of the Acanthocephala in Crompton and Nickol's (1985) book 'Biology of the Acanthocephala' and recognized the concepts of Meyer (1931, 1932, 1933) and Van Cleave (1936, 1941, 1947, 1948, 1949, 1951, 1952). This system became the standard for the taxonomy of this group and remains so to date. Many changes have taken place and many new genera and species, as well as higher taxa, have been described since. An updated version of the 1985 scheme incorporating new concepts in molecular taxonomy, gene sequencing and phylogenetic studies is presented. The hierarchy has undergone a total face lift with Amin's (1987) addition of a new class, Polyacanthocephala (and a new order and family) to remove inconsistencies in the class Palaeacanthocephala. Amin and Ha (2008) added a third order (and a new family) to the Palaeacanthocephala, Heteramorphida, which combines features from the palaeacanthocephalan families Polymorphidae and Heteracanthocephalidae. Other families and subfamilies have been added but some have been eliminated, e.g. the three subfamilies of Arythmacanthidae: Arhythmacanthinae Yamaguti, 1935; Neoacanthocephaloidinae Golvan, 1960; and Paracanthocephaloidinae Golvan, 1969. Amin (1985) listed 22 families, 122 genera and 903 species (4, 4 and 14 families; 13, 28 and 81 genera; 167, 167 and 569 species in Archiacanthocephala, Eoacanthocephala and Palaeacanthocephala, respectively). The number of taxa listed in the present treatment is 26 families (18% increase), 157 genera (29%), and 1298 species (44%) (4, 4 and 16; 18, 29 and 106; 189, 255 and 845, in the same order), which also includes 1 family, 1 genus and 4 species in the class Polyacanthocephala Amin, 1987, and 3 genera and 5 species in the fossil family Zhijinitidae.
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            Phylogenetic relationships among Syndermata inferred from nuclear and mitochondrial gene sequences.

            Phylogenetic relationships among Syndermata have been extensively debated, mainly because the sister-group of the Acanthocephala has not yet been clearly identified from analyses of morphological and molecular data. Here we conduct phylogenetic analyses on samples from the 4 classes of Acanthocephala (Archiacanthocephala, Eoacanthocephala, Polyacanthocephala, and Palaeacanthocephala) and the 3 Rotifera classes (Bdelloidea, Monogononta, and Seisonidea). We do so using small-subunit (SSU) and large-subunit (LSU) ribosomal DNA and cytochrome c oxidase subunit 1 (cox 1) sequences. These nuclear and mitochondrial DNA sequences were obtained for 27 acanthocephalans, 9 rotifers, and representatives of 6 phyla that were used as outgroups. Maximum parsimony (MP), maximum likelihood (ML), and Bayesian analyses were conducted on the nuclear rDNA(SSU+LSU) and the combined sequence dataset(SSU+LSU+cox 1 genes). Phylogenetic analyses of the combined rDNA and cox 1 data uniformly provided strong support for a clade including rotifers plus acanthocephalans (Syndermata). Strong support was also found for monophyly of Acanthocephala in analyses of the combined dataset or rDNA sequences alone. Within the Acanthocephala the monophyletic grouping of the representatives of each class was strongly supported. Our results depicted Archiacanthocephala as the sister-group to the remaining acanthocephalans. Analyses of the combined dataset recovered a sister-group relationship between Acanthocephala and Bdelloidea by parsimony, likelihood, and Bayesian methods. Support for this clade was generally strong. Alternative topologies that depicted a different rotifer sister-group of Acanthocephala (or monophyly of Rotifera) were significantly worse. In this paraphyletic assemblage of rotifers, the relative positions of Seisonidea and Monogononta to the clade Bdelloidea+Acanthocephala were inconsistent among trees based on different inference methods. These results indicate that Bdelloidea is the free-living sister-group to acanthocephalans, which should prove key for comparative investigations of the morphological, molecular, and ecological changes accompanying the evolution of parasitism.
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              Phylogenetic relationships of Palaeacanthocephala (Acanthocephala) inferred from SSU and LSU rDNA gene sequences.

              The Palaeacanthocephala is traditionally represented by 2 orders, Echinorhynchida and Polymorphida, with 10 and 3 families, respectively. To test the monophyly of the class, these 2 orders, and certain families, phylogenies were inferred using nuclear small-subunit (SSU) and large-subunit (LSU) ribosomal DNA sequences obtained for 29 species representing 10 families, 2 other classes of acanthocephalans, and 3 rotifer outgroups. Phylogenetic relationships were inferred by analyzing combined SSU and LSU sequences using maximum parsimony (MP) and maximum likelihood (ML) methods. Parsimony and ML trees inferred from combined analysis of these rDNA data strongly supported monophyly of Palaeacanthocephala and provided good resolution among species. Neither Polymorphida nor Echinorhynchida was monophyletic. Gorgorhynchoides bullocki (Echinorhynchida) was nested within the 6 species representing Polymorphida, and this clade was nested within species representing Echinorhynchida. Three of 4 palaeacanthocephalan families that could be evaluated were not monophyletic, and this finding was strongly supported. These results indicate that the family level classification of palaeacanthocephalans, which is mainly based on combinations of shared characters (not shared derived characters), needs to be reevaluated with respect to comprehensively sampled phylogenetic hypotheses.

                Author and article information

                EDP Sciences
                06 March 2019
                : 26
                : ( publisher-idID: parasite/2019/01 )
                [1 ] Institute of Parasitic Diseases 11445 E. Via Linda 2-419 Scottsdale AZ 85259 USA
                [2 ] Department of Biology, Brigham Young University 1114 MLBM Provo UT 84602 USA
                [3 ] Department of Animal Biology, Vegetal Biology and Ecology, Universitat Autònoma de Barcelona Cerdanyola 08193 Barcelona Spain
                [4 ] Department of Parasitology, Institute of Ecology and Biological Resources (IEBR), Vietnam Academy of Science and Technology 18 Hoang Quoc Viet Cau Giay Hanoi Vietnam
                Author notes
                [* ]Corresponding author: omaramin@ 123456aol.com
                parasite190006 10.1051/parasite/2019015
                © O.M. Amin et al., published by EDP Sciences, 2019

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                Page count
                Figures: 11, Tables: 6, Equations: 0, References: 48, Pages: 20
                Research Article


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