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Spiral valves from specimens of the giant electric ray Narcine entemedor Jordan & Starks, 1895 were examined in search of tapeworms at 2 localities of the Mexican tropical Pacific Ocean. Acanthobothrium oceguerai n. sp. is described herein based on material from Ventanilla, Oaxaca and from Acapulco Bay, Guerrero. The new species is a category 6 species, distinguished by being apolytic, retaining proglottids on the strobila until they are gravid, having strobila of 166-322 proglottids, having a small scolex and very long bothridia relative to the scolex, and having abaxial prongs that are short and thin in comparison to the axial prongs, which are longer and more robust. Acanthobothrium oceguerai n. sp. can be differentiated from other members of category 6 by the hooks, which are shorter, more robust, and smaller than those of the other members of this category. The phylogenetic analysis based on the 28S rRNA locus placed Acanthobothrium oceguerai n. sp. as sister to an unidentified species of larval Acanthobothrium from Philadelphia, Pennsylvania. In addition, sequences of the mitochondrial cytochrome oxidase subunit I gene and nuclear 18S rDNA were generated to provide support for future taxon sampling. Acanthobothrium oceguerai n. sp. is the fifth species of cestode reported from N. entemedor in the tropical eastern Pacific., (© American Society of Parasitologists 2024.)

Despite the large number of species described to date for the onchoprotepcephalid genus Acanthobothrium (207), only 16 named species have a genetic sequence. With this background, specimens of adult cestodes of the stingray Hypanus longus were collected off San Blas, Nayarit, and onchoproteocephalid larvae in the carangid fish Trachinotus rhodopus from Puerto Ángel, Oaxaca, both located on the Pacific coast of Mexico. The objective of this work is to investigate the phylogenetic position of these adults and larvae using nuclear ribosomal markers (18S rDNA and 28S rDNA). Morphologically, adult specimens were identified as Acanthobothrium cleofanus; larvae were identified only to family level. The phylogenetic position of both taxa was investigated based on the information of two nuclear molecular markers analyzed under Parsimony (PA) and Bayesian Inference (BI) methods. The newly generated sequences of A. cleofanus from Nayarit are identical to the sequences of several samples of Acanthobothrium sp. collected in the Mexican Pacific, which sequence are available in GenBank; DNA sequences obtained from onchoproteocephalid larva clearly place this taxon within Acanthobothrium but representing an independent lineage. In the resulting phylogenetic trees, Uncibilocularis okei was found nested within Acanthobothrium with an unstable position depending on the optimality criteria, indicating the need for more molecular analyzes with a greater number of species of both genera prior to define its phylogenetic relationships., (Copyright © 2021 Elsevier B.V. All rights reserved.)