Members of Polymorphidae, including Hexaglandula corynosoma, are acanthocephalans commonly found as intestinal parasites in marine mammals, fish-eating birds and waterfowl. Hexaglandula corynosoma is distributed throughout the Southeastern U. S. and southwards to Puerto Rico and Brazil. An acanthocephalan (and its larvae) resembling H. corynosoma were found parasitizing intermediate (decapod crustaceans, Uca spinicarpa) and definitive hosts (yellow-crowned night herons, Nyctanacea violacea) from various localities in Mexico. A morphological and genetic study, in combination with previous studies, confirmed that the larvae and adults were conspecific and corresponded to H. corynosoma. This is the first record of H. corynosoma in Mexico parasitizing intermediate and definitive hosts.

Three new diterpene alkaloids, (+)-8-epiagelasine T (1), (+)-10-epiagelasine B (2), and (+)-12-hydroxyagelasidine C (3), along with three known compounds, (+)-ent-agelasine F (4), (+)-agelasine B (5), and (+)-agelasidine C (6), were isolated from the sponge Agelas citrina, collected on the coasts of the Yucatán Peninsula (Mexico). Their chemical structures were elucidated by 1D and 2D NMR spectroscopy, HRESIMS techniques, and a comparison with literature data. Although the synthesis of (+)-ent-agelasine F (4) has been previously reported, this is the first time that it was isolated as a natural product. The evaluation of the antimicrobial activity against the Gram-positive pathogens Staphylococcus aureus, Streptococcus pneumoniae, Enterococcus faecalis showed that all of them were active, with (+)-10-epiagelasine B (2) being the most active compound with an MIC in the range of 1–8 µg/mL. On the other hand, the Gram-negative pathogenes Acinetobacter baumannii, Pseudomonas aeruginosa, and Klebsiella pneumoniae were also evaluated, and only (+)-agelasine B (5) showed a moderate antibacterial activity with a MIC value of 16 μg/mL.

Two new species of Parapharyngodon Chatterji, 1933 , parasitizing 3 species of hylid frogs (Diaglena spatulata, Triprion petasatus, and Trachycephalus typhonius) from Mexico are described. The 2 new species share the presence of a gubernaculum with Parapharyngodon lamothei and belong to the group of those species with short spicule; both differ from the remaining species of the genus in the papillar pattern on ventrolateral and dorsal lips and in the thickness of cuticular annulations and cuticular ornamentation in the female specimens. These are the third and fourth reports of Parapharyngodon spp. parasitizing hylid frogs. In addition to the egg characteristics, we propose that length of the lateral alae is also a taxonomically relevant feature to differentiate species of the genus. A bibliographic review of all species historically assigned to Parapharyngodon is given, including those that have been declared species inquirenda, or transferred to other genera and those that are considered valid.

A total of 51 sponges (Porifera) and 13 ascidians (Chordata) were collected on the coast of the Yucatan Peninsula (Mexico) and extracted with organic solvents. The resulting extracts were screened for antibacterial activity against four multidrug-resistant (MDR) bacterial pathogens: the Gram-negative Acinetobacter baumannii, Klebsiella pneumoniae, and Pseudomonas aeruginosa and the Gram-positive Staphylococcus aureus. The minimum inhibitory concentrations (MICs) of the organic extracts of each marine organism were determined using a broth microdilution assay. Extracts of eight of the species, in particular the Agelas citrina and Haliclona (Rhizoniera) curacaoensis, displayed activity against some of the pathogens tested. Some of the extracts showed similar MIC values to known antibiotics such as penicillins and aminoglycosides. This study is the first to carry out antimicrobial screening of extracts of marine sponges and ascidians collected from the Yucatan Peninsula. Bioassay-guided fractionation of the active extracts from the sponges Amphimedon compressa and A. citrina displayed, as a preliminary result, that an inseparable mixture of halitoxins and amphitoxins and (-)-agelasine B, respectively, are the major compounds responsible for their corresponding antibacterial activities. This is the first report of the antimicrobial activity of halitoxins and amphitoxins against major multidrug-resistant human pathogens. The promising antibacterial activities detected in this study indicate the coast of Yucatan Peninsula as a potential source of a great variety of marine organisms worthy of further research.

During January 2002, 3 specimens of an undescribed species of Oochoristica Lühe, 1898, were collected in Ctenosaura pectinata (Wiegmann, 1834) from Santa Mará Mixtequilla, Oaxaca, Mexico. Oochoristica leonregagnonae n. sp. differs from 71 of 82 species of the genus by its large number of testes (78-112 [95] vs. less than 65 per proglottid, respectively). In addition, the numerous ovarian lobes (31-79 [51]) possessed by the new species distinguish it from the other 10, with a maximum of 20 ovarian lobes. The new species differs from Oochoristica acapulcoensis Brooks, Pérez-Ponce de León and García-Prieto, 1999, which also infects C. pectinata in Mexico, by the presence of numerous staining granules throughout the parenchyma of the scolex in the latter species; likewise, testes in O. acapulcoensis reach and even overpass the excretory canals, whereas in the new species they are limited to the central region between these tubules.

A survey of adults of gryporhynchid tapeworms (Cestoda: Cyclophyllidea) from herons and related fish-eating birds (Ciconiiformes: Ardeidae and Threskiornithidae) along the Atlantic coast of Mexico from Tamaulipas to Yucatán is presented, based on the taxonomic evaluation of freshly collected specimens. They belong to the following 16 species (taxa reported as adults from Mexico for the first time are marked with an asterisk): Cyclustera capito (Rudolphi, 1819); Cyclustera ibisae (Schmidt and Bush, 1972); Dendrouterina ardeae (Rausch, 1955); *Dendrouterina (?) fuhrmanni (Clerc, 1906); D. (?) papillifera (Fuhrmann, 1908); *Dendrouterina pilherodiae Mahon, 1956; Glossocercus auritus (Rudolphi, 1819); *Glossocercus caribaensis (Rysavy and Macko, 1973); *Glossocercus cyprinodontis Chandler, 1935; *Glossocercus sp.; Neogryporhynchus cheilancristrotus (Wedl, 1855); *Paradilepis sp.; Parvitaenia cochlearii Coil, 1955; *Valipora campylancristrota (Wedl, 1855); *Valipora minuta (Coil, 1950); and Valipora m...