Two species ofAcanthobothrium(Onchoproteocephalidea: Onchobothriidae) are described from the spiral intestine ofNarcineentemedorJordan & Starks, 1895, in Bahía de Acapulco, Acapulco, Guerrero, Mexico. Based on the four criteria used for the identification of species ofAcanthobothrium,A.soniaesp. nov.is a Category 2 species (less than 15 mm in total length with less than 50 proglottids, less than 80 testes, and with the ovary asymmetrical in shape).Acanthobothriumvidalisp. nov.is a Category 6 species (more than 15 mm in total length with more than 50 proglottids, fewer than 80 testes, and the ovary is asymmetrical). The new species differ from similar species from the Pacific Ocean by total length, the number of proglottids, diameter of the accessory sucker, the length of the cirrus sac, the number of testes per proglottid and the measurements of hooks. With the recognition ofA.soniaesp. nov.andA.vidalisp. nov., 42 species ofAcanthobothriumhave been reported from the Pacific coast of the Americas. This is the first report of species ofAcanthobothriumfrom a member ofNarcinefrom Mexico and it brings the number of species reported from elasmobranchs from the Pacific Coast of Mexico to 13.

Species of Acanthobothrium have been documented as parasites of the spiral intestine of elasmobranchs. Results of a metadata analysis indicate that 114 species of elasmobranchs have been reported as hosts of 200 species of Acanthobothrium. The metadata analysis revealed that 3.7% of species of sharks and 14.9% of species of rays that have been reported as hosts to date; some species are parasitized by more than one species of Acanthobothrium. This work provides a Category designation, as proposed by Ghoshroy and Caira (2001), for each species of Acanthobothrium. These Category designations are a tool to facilitate comparisons among members of Acanthobothrium for descriptions of new species in the future.

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Three new species of Acanthobothrium Blanchard, 1848 (Onchoproteocephalidea: Onchobothriidae) are described from Pacific coastal waters of Mexico. Based on four criteria for categorization of species of Acanthobothrium, the three new species belong to Category 2 species, characterized by their total length (< 15 mm), number of proglottids (< 50) and testes (<80), and with asymmetrical ovary. Acanthobothrium ppdeleoni n. sp. from diamond stingray Hypanus dipterurus (Jordan & Gilbert) is differentiated from congeners by a combination of characters including total length of the whole worms, size of the scolex and bothridia, length of the bases of the hooks and abaxial prongs, and the size of the cirrus sacs in mature proglottids. Acanthobothrium hypanus n. sp. and A. sinaloaensis n. sp. are described from longtail stingray Hypanus longus (Garman). Acanthobothrium hypanus n. sp. is differentiated by a combination of characters including size of the scolex and bothridia, diameter of the accessory sucker, length of the abaxial prongs, size of the cirrus sacs and testes in mature proglottids. Acanthobothrium sinaloaensis n. sp. is differentiated by a combination of characters including size of the scolex and bothridia, diameter of the accessory sucker, size of the cirrus sacs in mature proglottids, number of immature proglottids, number of testes, the length of the lobes of the ovary and the absence of velum between medial margin of bothridia. Thirteen species of Acanthobothrium have been reported previously from elasmobranchs from the Pacific coast of Mexico. In the present study, the number of species is elevated to 16.