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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.

Metazoan parasite communities can experience temporal structural changes related to seasonal and/or local variations in several biotic and abiotic environmental factors. However, few studies have addressed this issue in tropical regions, where changes in water temperature are less extreme than in temperate regions, so the factors or processes that can generate variations in these parasite communities are as yet unclear. We quantified and analysed the parasite communities of 421 Lutjanus peru (Nichols & Murphy, 1922) collected from Acapulco Bay in Guerrero, Mexico, over a four-year period (August 2018 to April 2021), to identify any interannual variation due to local biotic and abiotic factors influenced by natural oceanographic phenomena, such as El Niño–Southern Oscillation, or La Niña. Twenty-five metazoan parasite taxa were recovered and identified: seven Digenea species; two Monogenea; one Cestoda; one Acanthocephala; four Nematoda; and ten of Crustacea (seven Copepoda and three Isopoda). The digeneans and copepods were the best represented parasite groups. The parasite communities were characterized by a high numerical dominance of helminth larvae. Species richness at the component community level (13 to 19 species) was similar to reported richness in other Lutjanus spp. The parasite communities of L. peru had a high variability in species composition, but low aggregate variability (e.g. species diversity), suggesting that structure of these communities may be quite stable over time. A clear interannual variation pattern was not observed, suggesting that parasite species of this host may respond differently to variations in environmental factors. Interannual variations were possibly caused by a combination of biotic (i.e. host feeding behaviour and body size) and local abiotic factors (influenced by climatic anomalies) which generated notable changes in the infection levels of several component species.

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A significant population of Chapultepec splitfin Girardinichthys viviparus was discovered in Lake Tecocomulco. Measurements of males and females and comments on the need for conservation of this locality are given.

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.