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Int J Parasitol Parasites Wildl
2019 Jul 10;10:281-288. doi: 10.1016/j.ijppaw.2019.09.008.
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New morphological and genetic data of Gigantorhynchus echinodiscus (Diesing, 1851) (Acanthocephala: Archiacanthocephala) in the giant anteater Myrmecophaga tridactyla Linnaeus, 1758 (Pilosa: Myrmecophagidae).
Nascimento Gomes AP
,
Cesário CS
,
Olifiers N
,
de Cassia Bianchi R
,
Maldonado A
,
Vilela RDV
.
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Gigantorhynchus echinodiscus (Diesing, 1851) is a parasite of anteaters in South America. Although described by Diesing in 1851, there is still a lack of taxonomic and phylogenetic information regarding this species. In the present study, we redescribe G. echinodiscus collected from a giant anteater, Myrmecophaga tridactyla Linnaeus, 1758, from the Brazilian Cerrado (Savannah) in the State of São Paulo by light and scanning electron microscopy. In addition, phylogenies were inferred from partial DNA gene sequence of the nuclear large subunit ribosomal RNA gene (28S rRNA). We provide for the first time details of the proboscis with a crown having 18 large hooks and numerous small hooks, a lateral papilla at the base of the proboscis, a ringed pseudo-segmented body, large testes, cemented glands in pairs, and a non-segmented region in the posterior end of the body, which contributed to the diagnosis of the species. Molecular phylogenetic analyses recovered G. echinodiscus forming a well-supported monophyletic group with Mediorhynchus sp., which was congruent with morphological studies that allocate both genera within the family Gigantorhynchidae. In conclusion, the present work adds new morphological and molecular information, emphasizing the importance of adopting integrative taxonomic approaches in studies of Acanthocephala.
Figs.1–6. Line drawing of Gigantorhynchus echinodiscus from Mymercophaga tridactyla. 1. Praesoma with the proboscis presenting a crown with robust hooks followed by small hooks, a receptacle proboscis, and papillae in the base of the neck; 2. Three different robust hooks in the crown and a one small type in the proboscis; 3. Unsegmented anterior part of the trunk, and lemnisci filiform reaching the middle region of the trunk; 4. Posterior region of adult male showing reproductive organs; 5. Posterior region of adult female showing the uterus, vagina and gonopore subterminal; 6. Egg.
Figs. 7–11. Light microscopy of adult Gigantorhynchus echinodiscus from Mymercophaga tridactyla. 7. Proboscis with a crown of large hooks in the apex and small hooks, and a proboscis receptacle (Re); 8. Trunk with pseudo segmentation (arrows) and the end of the lemnisci (Le); 9. Male reproduction organs, testis (Te), cement glands in pair (Cgl), ejaculatory duct (Ed); 10. Detail of the posterior end of adult female showing the uterus (Ut), vagina (Va, arrow) and gonopore subterminal (Gp); 11. Egg ellipsoid showing the outer membrane thick (Om), inner membrane (Im) thin, embryo (Em).
Fig. 12–17. Scanning electron micrographs of adult Gigantorhynchus echinodiscus from Mymercophaga tridactyla. 12 and 13. Cylindrical proboscis armed with hooks (Ho) showing a space (Sp) between the two circles of large hooks and small rootless spines, neck (Ne), trunk (Tr), lateral papillae (Pa, arrowhead); 14. Detail of the crown with two circles of large hooks (arrow – 1st row and asterisk – 2nd row); 15. Detail of the lateral papillae; 16 and 17. Posterior end of adult male showing the region without pseudo-segmentation (cross) and a copulatory bursa protruding from the body (CB).
Fig. 18. Bayesian inference phylogenetic reconstruction tree of 28S rRNA gene sequences of G. echinodicus in the present study (in red and bold) and archiacanthocephalans sequences from GenBank. The class Palaeacanthocephala, and Eoacanthocephala were added as outgroups. Node values are MP-BP, aLRT, ML-BP, and BPP, respectively.* no support or node not recovered in the respective analysis. Blue – family Oligacanthorhynchidae; green – family Moniliformidae; red – family Gigantorhynchidae.
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