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Members of the genus Maritrema Nicoll, 1907 include endoparasites of aquatic birds and mammals, distributed worldwide. Adult specimens were collected from the intestines of three bird species (the great black hawks, Buteogallus urubitinga Gmelin; laughing gull, Leucophaeus atricilla Linnaeus; and the willet, Tringa semipalmata Gmelin) in three localities along the Gulf of Mexico. Photogenophores were sequenced for the large subunit (LSU) from nuclear rDNA, and the new sequences were aligned with other microphalloid sequences available in GenBank. The maximum likelihood and Bayesian inference analyses revealed three independent lineages, one corresponding to a previously described species, Maritrema corai Hernández-Orts, Pinacho-Pinacho, García-Varela & Kostadinova, 2016, and two representing two undescribed species. These two new species are described in the current study. Maritrema itzamnai n. sp. can be morphologically differentiated from its four congeneric species occurring in coastal areas of Mexico by having smaller oral (20-29 × 20-38 μm) and ventral (20-39 × 19-33 μm) suckers. In addition, Maritrema itzamnai n. sp. possess annular vitellarium instead of a horseshoe-shaped vitellarium. Maritrema kukulkanni n. sp. can be distinguished from its congeneric species reported from Mexico by possessing a larger oesophagus (44-117μm) and by having a vitellarium distributed in both the hindbody and forebody. Maritrema corai is the third species recorded in this study parasitizing the great black hawk ( Buteogallus urubitinga ); this represents a new host and locality record, expanding its distribution range from the Mexican Pacific Ocean to the Gulf of Mexico.

Echinochasmids are a group of globally distributed digeneans, and the adults are found in the intestines of birds, mammals and reptiles. In the Neotropical region of Mexico, adult specimens were obtained from seven fish-eating bird species in six localities, whereas specimens of Stephanoprora aylacostoma were obtained experimentally in Argentina. Morphologically, the new specimens from the Neotropical region of Mexico were identified as Stephanoprora uruguayense and an undescribed species of Echinochasmus. Sequences for two nuclear (large subunit (28S) and internal transcribed spacer from DNA ribosomal (ITS1-5.8S-ITS2)) molecular markers were generated and analysed together with other sequences downloaded from GenBank. The phylogenies obtained with each molecular marker indicated that Echinochasmus is paraphyletic and agreed with previous phylogenetic studies. The first cluster included the type species (E. coaxatus, which has 24 head-collar spines) plus three congeneric species. The second cluster contained species of Echinochasmus plus Stephanoprora, including the species analysed herein, S. uruguayense, S. aylacostoma (with 22 head-collar spines) and Echinochasmus sp. (with 20 head-collar spines), which formed three independent subclades, allowing us to recognize a lineage that was described morphologically as a new species. Echinochasmus ostrowskiae n. sp. can be distinguished from its congeners by having a head collar with 20 spines in a single row, seven spines on each edge and three angle spines, and a pharynx with an irregular edge and by the body, egg and collar spine sizes. Additionally, new host and locality records for S. uruguayense are presented, expanding its geographical distribution range in the Americas., Competing Interests: Declaration of competing interest The authors declare there are no conflicts of interest., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Parastrigea brasiliana (Szidat, 1928) Dubois, 1964, was described from (Cochlearius cochlearius) in South America. The taxonomy of this species has been unstable due that it was described as a member of Strigea Abildgaard, 1790. However, the same author one year later transferred it to Apharyngostrigea Ciurea, 1927 and since then, it has been alternatively placed in the genus Apharyngostrigea or Parastrigea Szidat, 1928 from Strigeidae. In the current research, specimens identified as P. brasiliana were collected from type host in southeastern Mexico. We sequenced three molecular markers: the internal transcribed spacers ITS1 and ITS2 including the 5.8S gene (ITS region), the D1-D3 domains of the large subunit (LSU) from nuclear DNA and cytochrome c oxidase subunit I (cox 1) from mitochondrial DNA. These sequences were aligned with other sequences available in the GenBank dataset from Strigeidae. Maximum likelihood and Bayesian analyses inferred with three molecular markers consistently showed that P. brasiliana is not closely related to other members of the genus Parastrigea and are placed in a reciprocal monophyletic clade inside Apharyngostrigea, with very low genetic divergence, varying from 0 to 0.09% for the ITS, from 0 to 0.08% for the LSU and from 0.21 to 0.43% for cox 1. Consequently, we proposed to reallocate it to A. brasiliana. The phylogenetic analyses obtained are key and very useful for re-evaluate the morphology of A. brasiliana because this species share morphological characters with the genera Parastrigea (concentration of vitelline follicles distributed in two lateral expansions on the forebody) and Apharyngostrigea (absence of pharynx). Finally, the current record of A. brasiliana expands its distribution range in four countries, namely, the USA, Mexico, Venezuela and Brazil, in the Neotropical region., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Species in the genus Gorgoderina Looss, 1902 are parasites of the urinary bladder of amphibians and include around 50 species described globally. Molecular data on species of the genus are scarce, as is the information of their life-cycle patterns. During a survey on the genetic characterization of the frog trematodes in the tropical rain forest of Los Tuxtlas, in the Gulf of Mexico slope of Mexico, specimens of two morphotypes of Gorgoderina were sampled from the Rio Grande leopard frog, Rana berlandieri. One of them represented an undescribed species which is described herein as Gorgoderina rosamondae n. sp., whereas the other one was morphologically very similar to an apparently widely distributed North American species, G. attenuata, which has been previously reported in the same geographical area. Specimens of both morphotypes were sequenced for two nuclear and one mitochondrial genes. Phylogenetic trees corroborated the distinction of the new species, and data on the internal transcribed spacer 2 revealed genetic differences between G. attenuata sequenced from frogs in USA and specimens of Gorgoderina sp. from Los Tuxtlas, indicating the possibility that they also represent an undescribed species. COI sequences showed high genetic divergence values between the new species and Gorgoderina sp. from Los Tuxtlas (8.63-9.99%). Additionally, COI sequences of the larval forms (sporocyst, cercariae and metacercariae) sampled in the same locality from their first and second intermediate hosts (Pisidium sp. and Agriogomphus tumens, respectively) showed conspecificity, and the 3 host life-cycle of the new species was elucidated., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Translocation of fishes for aquaculture has resulted in the co-introduction of some of their parasites. African cichlid fishes, generically called "tilapias" have been introduced worldwide, along with their monogenean parasites. In a nation-wide survey, we characterised monogeneans of the genus Gyrodactylus infecting farmed "tilapia" throughout Mexico. We also collected native fishes around farms, to look for potential parasite spillover from cultured fishes. Monogeneans were identified taxonomically using morphological and molecular characters. Originally African, pathogenic Gyrodactylus cichlidarum was recorded in every farm surveyed, infecting different "tilapia" varieties, as well as three native cichlid fish species. Previously, we had shown that G. cichlidarum also infects native, non-cichlid fishes in Mexico. We also recorded that Gyrodactylus yacatli is widely distributed in Mexico, infecting cultured "tilapia" and native fishes; and present data indicating that this is a further translocated African parasite. A third, unidentified gyrodactylid infected farmed and native fishes in Chiapas, southern Mexico; we describe the new species as Gyrodactylus shinni n. sp., and provide evidence that this is a third monogenean translocated with African fish. The wide distribution of exotic parasites co-introduced with "tilapia" and their spillover to native fishes may have an important impact on the ichthyofauna in Mexico, one the world's megadiverse countries.

A new genus and species of Hexabothriidae Price, 1942 is described from specimens infecting the gill of the numbfish Narcine entemedor Jordan and Starks from the Pacific coast of Mexico. In addition to the new taxon described here, species of 8 genera also display symmetrical haptors and have eggs with two polar filaments. However, they differ in the combination of the following features: distal portion of the male copulatory organ tubular, unarmed and proximally dilated confining an internal coiled duct, as well as dorsal origin of haptoral appendix. Based on molecular data derived from 3 loci, the mitochondrial Cytochrome C oxidase subunit 1 as well as the nuclear ribosomal 18S and 28S, the new species was found nested within Hexabothriidae together with the other 4 genera with representatives in GenBank. This is the first species of Hexabothriidae reported from a species of Narcinidae., (Copyright © 2020 Elsevier B.V. All rights reserved.)

A new species of microphallid trematode was collected from the intestine of the yellow-crowned night heron Nyctanassa violacea (L.) (Pelecaniformes: Ardeidae) from Veracruz, Mexico. Maritrema kostadinovae n. sp. differs distinctly from other members of Maritrema Nicoll, 1907 from the Americas by its smaller body size (262-435 × 242-363 μm), the extension of caeca (reaching to anterior level of ventral sucker), the size and shape of the cirrus (short, tubular and unarmed) and metraterm (simple and thin-walled), the position of the genital pore (sinistrolateral to ventral sucker) and the arrangement of the vitellaria (horseshoe-shaped with posteriorly directed opening). Maximum likelihood and Bayesian inference analyses, based on partial 28S rDNA sequences, depicted M. kostadinovae n. sp. within the genus Maritrema with strong support. The new species is in a sister position to other available members of Maritrema, except for M. subdolum Jägerskiöld, 1909 that branches as the early divergent species in the Maritrema clade. The new species is the third species of Maritrema described from birds in Mexico. Comparative morphometric data for Maritrema taxa from birds and mammals from the Americas is provided.

In an ongoing investigation on the helminths of amphibians in southeastern Mexico, specimens of 2 undescribed species of Haematoloechus were collected from Rana brownorum . Haematoloechus ceciliae n. sp. is morphologically most similar to Haematoloechus meridionalis , but differs in the shape of the oral sucker, in the nature of the acetabulum, and in the distribution of the glandular cells in the pharyngeal region; Haematoloechus celestunensis n. sp. closely resembles Haematoloechus floedae , but differs in the form and size of the testes and measurements of acetabulum. COI and 28S DNA sequences of both new species show high divergence compared to other species of the genus. In the phylogenetic trees, H. ceciliae appears most closely related to Haematoloechus danbrooksi and H. celestunensis to Haematoloechus veracruzanus .

Gyrodactylus mojarrae n. sp. is described from the gills of the Neotropical cichlids Thorichthys maculipinnis, Rocio octofasciata, Vieja zonata and V. fenestrata from several localities across southern Mexico. The new species is erected on the basis of the morphology of the haptoral elements (anchors, bars and hooks), and its phylogenetic position within the Gyrodactylidae is evaluated based on the analysis of partial sequences of the ITS1, 5.8 rRNA gene and ITS2. Gyrodactylus mojarrae n. sp. differs from other congeneric species by having hooks with a straight shaft and recurved point, pointed toe and convex heel, presence of reduced superficial anchor roots, by the number and disposition of spinelets of the male copulatory organ, and the absence of shield and lateral processes of the superficial bar. Molecular circumscription of isolates of G. mojarrae n. sp. from different host and hydrological basins showed that these isolates are conspecific and represent a distinct lineage from other congeners, including newly sequenced isolates of Gyodactylus sp. A and Gyrodactylus sp. B from Astyanax mexicanus (Characidae) and Gobiomorus dormitor (Eleotridae), respectively. Genetic affinities of Gyodactylus sp. A and B indicate that they might represent undescribed species infecting freshwater fish from the Americas., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Integrative taxonomy uses several sources of information to establish more robust species delimitation criteria. In this study, we followed that approach to describe two new species of allocreadiid trematodes from freshwater fish distributed in locations across Middle America. The new species were first recognized by using sequences of the domains D1-D3 of the ribosomal 28S rRNA gene and then, morphological data (light and scanning electron microscopy (SEM)), host association, and geographical distribution were considered as additional sources of information to complement the species delimitation and description. Auriculostoma tica n. sp. was found in the intestine of Gymnotus maculosus Albert and Miller in Costa Rica, while Wallinia anindoi n. sp. was found in the intestine of Astyanax aeneus (Günther) in Oaxaca and Chiapas, Mexico, as well as in a location of Guatemala. A phylogenetic analysis combining newly generated sequences of the two new species along with those available for other allocreadiids in GenBank, revealed that isolates of each species are reciprocally monophyletic, and also their interrelationships: Au. tica n. sp. is a sister taxon of Auriculostoma totonacapanensis Razo-Mendivil et al., 2014, and W. anindoi n. sp. is a sister taxon of Wallinia brasiliensis Dias, et al., 2018. Genetic distances for the 28S rRNA gene were estimated among the American species of allocreadiids and further supported the validity of the new species.

In the present study, two new species of Gyrodactylus are described from Profundulus oaxacae, a fish endemic to the Pacific slope of Oaxaca State, Mexico. Fishes were collected within their distribution range in 5 localities in the Atoyac-Verde River. Gyrodactylus montealbani n. sp. and G. zapoteco n. sp. were erected and characterized morphologically (sclerites of the attachment apparatus and the male copulatory organ) and molecularly (sequences of the Internal Transcribed Spacer region of rDNA). The haptoral sclerites of the new species are similar to those of Gyrodactylus iunuri and Gyrodactylus tepari, both recently described from the goodeid fish Goodea atripinnis, from the Mexican States of Jalisco and Querétaro, respectively; and to Gyrodactylus xtachuna described from the poeciliid Poeciliopsis gracilis in Veracruz State, Mexico - nonetheless, these species can all be discriminated based on their marginal hook morphology. Specimens of G. montealbani n. sp. and G. zapoteco n. sp. were sequenced, and were aligned with sequences of 25 other Gyrodactylus spp. Both Maximum likelihood and Bayesian inference analyses indicated that the two new species are members of independent, well-supported lineages - these are the first Gyrodactylus species described from Profundulus oaxacae., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Parasitological examination of the maya needlefish Strongylura hubbsi Collette (Belonidae) from the Rio Lacantún basin in the Montes Azules Biosphere Reserve, Chiapas, Mexico showed that specimens were parasitized by two monogenean species in two different sites: Paracolpenteron hubbsii n. gen., n. sp in the urinary bladder and Ancyrocephalus chiapanensis n. sp in the gill lamellae. Paracolpenteron hubbsii differs from other dactylogyrid species without a haptoral anchor/bar complex infecting the urinary systems, gills and nasal cavities by the general morphology of hooks, a dextral vaginal opening, a tubular male copulatory organ comprising a base from which a coiled shaft arises in counterclockwise direction, and an unarticulated Y-shaped accessory piece. Ancyrocephalus chiapanensis n. sp. resembles Ancyrocephalus cornutus William & Rogers, 1972 from the gills of Strongylura marina from Florida from which it differs in possessing a twisted tube of the male copulatory organ (curved in A. cornutus), ventral bar with cavities on the ends (cavities absent in A. cornutus) and by the size of the ventral (length 31-34 μm vs. 24-27 μm in A. cornutus) and dorsal (length 25-28 μm vs. 18-22 μm in A. cornutus) anchors. These new monogeneans are described herein and their biogeography is briefly discussed based on the previous phylogenetic hypotheses concerning the host family., (© E.F. Mendoza-Franco et al., published by EDP Sciences, 2018.)

In central Mexico, populations of the freshwater snail Physella cubensis were infected with metacercariae from a species of Echinoparyphium (Digenea: Echinostomatidae). In the current study, we describe both larval and adult stages of this species obtained from experimental and natural infections. A total 180 snails were collected from Patzcuaro Lake, Michoacan state in central Mexico in July 2012. In the laboratory snails were placed in individual vials and exposed to light with the aim of observing emergence of cercariae. To obtain metacercariae, uninfected snails (P. cubensis) were exposed to cercariae. Chicks were infected with metacercariae to obtain adults. Nine days post-infection, eggs were recovered and incubated in tap water at room temperature to observe miracidia. Adults obtained from natural and experimentally infected hosts possess a head collar with 45 spines in two alternating rows, confirming the identification as Echinoparyphium recurvatum von Linstow 1873. To test the conspecificity of all stages, sequences of nuclear internal transcribed spacer 1 (ITS1), 5.8S and ITS2 rDNA were obtained from two adult worms recovered from chicks and also a natural avian host, the shoveler duck Anas clypeata, together with five cercarial and four metacercarial isolates from nine snails. The genetic divergence estimated among the 13 isolates was very low, ranging from 0 to 0.6%. Phylogenetic analyses inferred by maximum likelihood and Bayesian methods showed that all isolates of E. recurvatum form a single clade with strong support. The presence of E. recurvatum in P. cubensis and A. clypeata from central Mexico represents new host reports, and extends the distribution range in the Americas.

Phyllodistomum spinopapillatum sp. nov. is described from the urinary bladder of the Oaxaca killifish, Profundulus balsanus Ahl (Profundulidae) in Rio Pueblo Viejo and Rio Santa Cruz, Oaxaca, southwestern Mexico. The new species is described based on evidence gathered from morphology, scanning electron microscopy (SEM), and partial sequences of the 28S rRNA gene. Diagnostic characters of the new species of Phyllodistomum Braun 1899 are the presence of spines on the entire body surface and having a ventral sucker almost half the size of oral sucker. The new species possess a large number of dome-like papillae on the body surface with scattered distribution along the hindbody, and these papillae are characteristically spinulated. Phyllodistomum spinopapillatum sp. nov. most closely resembles P. inecoli Razo-Mendivil, Perez-Ponce de Leon and Rubio- Godoy, 2013, a parasite of the twospot livebearer Pseudoxiphophorus bimaculatus (Heckel) from Veracruz, in the Atlantic slope of Mexico. In addition to the new species, specimens of P. inecoli were also found parasitising the urinary bladder of cyprinodontiforms such as the Mexican molly Poecilia sphenops Valencienes in a pond at Santa Maria Coyotepec, and in Profundulus sp. in Rio Templo, both in Oaxaca, and in the Porthole livebearer Poeciliopsis gracilis (Heckel) in Rio San Juan, as well as in Profundulus punctatus (Gunter) from Rio Nueva Francia, both in Chiapas. The distribution and host range of P. inecoli is extended to freshwaters of the Pacific slope of Mexico, and to other cyprynodontiforms.

Aristocleidus mexicanus n. sp. and Aristocleidus lacantuni n. sp. are described from the gills of the Mexican mojarra Eugerres mexicanus (Gerreidae, Perciformes) from the Rio Lacantún basin, Chiapas State, Mexico. These new species differ from previously described congeneric species in the characteristics of several structures, including: (a) ventral anchors, with differences in length (i.e. 46-50 µm in A. mexicanus vs. 38-43 µm, 34-37 µm, and 26-33 µm in Aristocleidus hastatus Mueller, 1936, Aristocleidus sp. of Mendoza-Franco, Violante-González & Roche 2009, and Aristocleidus lamothei Kritsky & Mendoza-Franco, 2008, respectively) and shape (i.e. slightly angular union of elongate arcing shaft and point in A. mexicanus vs. point and shaft united at a conspicuous angular bend in A. hastatus and Aristocleidus sp., and evenly curved shaft and point in A. lamothei); (b) male copulatory organ, i.e. a coiled tube with less than one ring in A. mexicanus and A. lacantuni (vs. a coiled tube of about 1½ in Aristocleidus sp.); (c) distal end of the accessory piece (ornate in A. mexicanus vs. distally flattened and trifid in A. hastatus and A. lamothei, respectively); (d) vaginal tube (moderately long in A. mexicanus vs. short in A. lamothei and looping in Aristocleidus sp.); and (e) ventral bar (anteromedial process with terminal horn-like ornamentation in A. lacantuni vs. ornamentation absent in the other species). This study reports for the first time species of Aristocleidus from freshwater environments in Mexico., (© E.F. Mendoza-Franco et al., published by EDP Sciences, 2015.)

Parastrigea plataleae n. sp. (Digenea: Strigeidae) is described from the intestine of the roseate spoonbill Platalea ajaja (Threskiornithidae) from four localities on the Pacific coast of Mexico. The new species is mainly distinguished from the other 18 described species of Parastrigea based on the ratio of its hindbody length to forebody length. A principal component analysis (PCA) of 16 morphometric traits for 15 specimens of P. plataleae n. sp., five of Parastrigea cincta and 11 of Parastrigea diovadena previously recorded in Mexico, clearly shows three clusters, which correspond to the three species. DNA sequences of the internal transcribed spacers (ITSs) of ribosomal DNA and the mitochondrial gene cytochrome c oxidase subunit I (cox 1) were used to corroborate this morphological distinction. The genetic divergence estimated among P. plataleae n. sp., P. cincta and P. diovadena ranged from 0.5 to 1.48% for ITSs and from 9.31 to 11.47% for cox 1. Maximum parsimony (MP) and maximum likelihood (ML) analyses were performed on the combined datasets (ITSs+cox 1) and on each dataset alone. All of the phylogenetic analyses indicated that the specimens from the roseate spoonbill represent a clade with strong bootstrap support. The morphological evidence and the genetic divergence in combination with the reciprocal monophyly in all of the phylogenetic trees support the hypothesis that the digeneans found in the intestines of roseate spoonbills represent a new species., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

During an inventory of parasites of anurans in Occidental Mexico, an apparently undescribed species of Halipegus was found under the tongue of Rana psilonota Webb, 2001. The objective of this study is to describe this new species. Halipegus psilonotae differs from all other congeners by the combination of the following characters: parasite under the tongue of frogs, body size small, ventral sucker representing 0.19-0.2 of body length, ovary smaller than testes, egg filament short (27.5-40).

Paracreptotrema heterandriae n. sp. (Trematoda: Allocreadiidae) is described from the intestine of the freshwater fish Heterandria bimaculata (Teleostei: Poeciliidae) from the upper basin of Río La Antigua, in Veracruz, Mexico. The new species is distinguished from the 3 others in the Paracreptotrema Choudhury, Pérez-Ponce de León, Brooks, and Daverdin, 2006 , mainly by having a feeble membranous cirrus sac containing an uncoiled seminal vesicle, instead of a well-developed muscular cirrus sac that encloses coiled seminal vesicle, pars prostatica, and ejaculatory duct as in the previously 3 nominal species. Moreover, eggs of the new species are larger than all others ([measurements in micrometers] eggs of P. heterandriae n. sp. 72.5 [70-75] × 40 [35-41]; P. blancoi 55.4 [52.5-62.5] × 38.5 [32.5-42.5]; P. mendezi 46 × 37; P. profundulusi 57 [52-60] × 27.8 [25-30]).

Paracreptotrema profundulusi n. sp. (Trematoda: Allocreadiidae) is described from the intestine of the freshwater fishes Profundulus punctatus and P. balsanus (Teleostei: Profundulidae) from the Tehuantepec and the Atoyac-Verde River basins, in Oaxaca, México, in the western extreme of Central America. The new species is distinguished from Paracreptotrema blancoi Choudhury, Pérez-Ponce de León, Brooks, and Daverdin, 2006 , to which it is most similar, and from P. mendezi (Sogandares-Bernal, 1955) Choudhury, Pérez-Ponce de León, Brooks, and Daverdin, 2006 , by the caeca extending beyond the testes, vitelline follicles that invade the postesticular area, and uterus with transverse loops located mainly between the testes and the genital pore. Paracreptotrema blancoi was collected from the same host species and also from Profundulus oaxacae. Here, we provide data that show its broad distribution in several river basins of Neotropical southern México, including the Papagayo River basin, Guerrero, México, and the Atoyac-Verde and Tehuantepec river basins, and other rivers in Oaxaca, México. Freshwater fishes of the Profundulidae are endemic to Central America and host a helminth fauna that includes at least 4 species found only in these hosts.

The genus Langeronia parasitizing the intestine of several species of anurans is distributed from North to Central America. We identified Langeronia macrocirra and Langeronia cf. parva from the same host and localities, and present here new data not applicable about their tegumental surface by scanning electron microscopy. We compared sequences of the rDNA ITS2 region and mtDNA cox1 gene for the two morphotypes. ITS2 exhibited a high degree of conservation. Phylogenetic reconstruction using cox1 revealed three clades (I, II, and III), which did not correspond to a previous identification or host. Little divergence was found within clades: sequences were identical in clade I, whereas clade II had 0.27% and clade III had 1.08%. Inter-clade divergence reached 8.69% (I vs. III). This pattern of genetic divergence indicated that both taxa probably belong to the same species, so we posit that the morphological changes could be correlated with development. Increasing sample size and geographical coverage will contribute to the taxonomy of the genus based on morphological and molecular evidence, and will open tracks toward the use of DNA barcodes to the genus in Mexico.

Oligogonotylus mayae n.sp. is described from the intestine of the Mayan cichlid Cichlasoma urophthalmus (Günther) in Ría Lagartos, Ría Celestún, and Estero Progreso, Yucatán State. This is the second species described for Oligogonotylus Watson, 1976, the other being O.manteri Watson, 1976. The new species is readily distinguished from O. manteri by the anterior extension of the vitelline follicles. In O. Manteri, Vitelline follicles are found entirely in the hindbody, extending posteriorly to mid-testicular level. Vitelline follicles in the new species extend from teh anterior margin of posterior testis to the region between the bentral sucker and the pharynx. comparison of approximately 1,850 bases of ribosomal DNA (ITS1, ITS2, 5.8S, and 28S), and 400 bases of cytochrome c oxidase subunit I (cox1) strongly supports the status of O. mayae as a new species, as compared to O. manteri collected from cichlids in other localities of Mexico, Belize, and Guatemala.

We describe herein the first occurrence of the monogenean Urocleidoides vaginoclaustrum in the wild. This monogenean was originally described from an aquarium neotropical fish examined in India. Worms were collected from the gills of Xiphophorus hellerii, a species native to tropical Mexico but introduced to the Los Berros Spring in the State of Durango, Northern Mexico. These specimens showed slight morphological differences in the sclerotized structures of the haptor with respect to the specimens described from India. A brief morphological characterization of this species is presented.

While investigating the parasites of several marine fishes from the Western Atlantic, the Southern Gulf of Mexico and Central America (Panama), the following monogenoidean species from the gills of gerreid fishes (Gerreidae) were found: Diplec-tanum gatunense sp. n. (Diplectanidae) and Octouncuhaptor eugerrei gen. et sp. n. (Dactylogyridae) in Eugerres brasilianus (Cuvier) from Gatun Lake in the Panama Canal Watershed, and Diplectanum mexicanum sp. n. in Diapterus rhombeus (Cuvier) from the coast of Campeche State, Mexico. New diplectanid species are distinguished from other species of the genus by the general morphology of the copulatory complex and by the shape of the anchors and bars on the haptor. Octouncuhaptor gen. n. is proposed for its new species having slightly overlapping gonads (testis posterodorsal to the ovary), a dextrolateral vaginal aperture, a copulatory complex consisting of a coiled male copulatory organ with counterclockwise rings with the base articulated to the accessory piece, 8 pairs of hooks and the absence of anchors and bars on haptor. Our analysis of morphological features of Diplectanum species on gerreids evidences that these parasites more closely resemble each other than the known species from sciaenids suggesting that split between gerreids and sciaenids resulted in parasite speciation.

Prodistomum lichtenfelsi n. sp. (Digenea: Lepocreadiidae) is described; it was obtained from the intestine of the longtail bass, Hemanthias leptus (Ginsburg), collected from the Bay of Campeche in the Gulf of Mexico. This is the first record of a parasite from this host. Prodistomum lichtenfelsi n. sp. is similar to P. hynnodi, P. menidiae, and P. waltairensis in that it possesses a prepharynx that is distinctly shorter (153 microm [110-210] long) than the combined length of the esophagus (163 microm [110-220] long) and the pseudoesophagus (137 microm [120-170] long), but it differs from them in having an excretory vesicle that extends into the forebody, a smooth ovary and testes, and vitellaria that extend to the posterior level of the esophagus. An updated key to the 12 nominal species within Prodistomum is given, and the diagnosis of the genus is emended to include species possessing a sinuous external seminal vesicle.

A new species of Crassicutis Manter, 1936 is described from the Sinaloan cichlid Cichlasoma beani (Jordan) (Osteichthyes: Cichlidae) in the upper Río Santiago basin. Crassicutis choudhuryi n. sp. differs from most of the other nominal species by having testes located in a symmetrical position. The only other species of the genus that includes some specimens exhibiting this trait is Crassicutis intermedius (Szidat 1954), a species found in 5 species of siluriforms and 1 species of characiform in South America. However, this species differs from Cr. choudhuryi n. sp. by having testes almost half of the size, and vitelline follicles extending anteriorly to the region between the acetabulum and the intestinal bifurcation. The new species is morphologically very similar to Crassicutis cichlasomae Manter, 1936, but clearly differs from this species because of the constantly symmetrical position of the testes. Additionally, Cr. choudhuryi n. sp. is found in the Santiago River basin on the Pacific slope of Mexico, parasitizing specifically the endemic Ci. beani that does not co-occur with any other cichlid. Cr. cichlasomae exhibits more hosts (about 25 species of cichlids only in Mexico) and a wider distribution range that extends from northeastern Mexico southward to Central America, Cuba, and Brazil. To corroborate that our specimens were not conspecific with Cr. cichlasomae, sequences of the internal transcribed spacer (ITS1) and the 28S ribosomal RNA genes of individuals from several populations (recently collected in southeastern Mexico) were obtained and compared to the species described herein. Sequence divergence (1.3% for the 28S and 4.0% for the ITS1) gives further support to the erection of a new species.

Gorgoderina festoni n. sp. is described from the urinary bladder of Gastrophryne usta, Leptodactylus labialis, L. melanonotus and Bufo marinus from localities at low altitude in the states of Veracruz, Oaxaca, Guerrero and Colima, Mexico. This species differs from most other species of the genus by a combination of the following characters: lobed vitelline masses, body size 3.45-4.26 (mean 3.75) mm and sucker-ratio 1:1.3-1.52 (mean 1:1.44). The new species shares these three features with G. bilobata Rankin, 1937, G. schistorchis Steelman, 1938, G. tenua Rankin, 1937, G. vitelliloba (Olsson, 1876) and G. cryptorchis Travassos, 1924, but it differs from the first four in having gonads with entire margins. G. festoni most closely resembles G. cryptorchis, but differs from this species in body width at the level of the ventral sucker and in the absence of oesophageal glands. The autapomorphy that distinguishes G. festoni from all other members of the genus is the presence of a tegumental extension (festoon) on the external margin of the ventral sucker.

Haematoloechus floedae was originally described from the lungs of Rana catesbeiana in Texas, and later reported in Florida, in the United States. It was proposed to be synonymous with H. breviplexus, H. parviplexus, and H. varioplexus. We obtained specimens of H. floedae from Rana brownorum and R. vaillanti in Yucatán, Mexico; R. cf. forreri and R. taylori in Guanacaste, Costa Rica; and R. catesbeiana in Georgia and California. Some specimens were processed for morphological study; sequences of the 28S of the rDNA and the mitochondrial COI were obtained from several specimens of each population. Phylogenetic analysis of molecular data indicates studied populations constitute a single taxon, different from H. varioplexus, H. breviplexus, and H. parviplexus. Some morphological characters remain constant among populations of H. floedae, and are useful for differentiating this species. These include the oral sucker-pharynx ratio, oral sucker-ventral sucker ratio, ovary and testes shape, extension of uterine longitudinal loops, and extension of vitelline follicles (in fully developed worms). Sequence homogeneity among populations of H. floedae suggests a recent spread, perhaps due to the introduction of R. catesbeiana for culture to the western United States, southeast Mexico, and Costa Rica.

Glypthelmins Stafford, 1905 includes 29 putative species commonly found in the intestine and liver of anurans from all over the world but mainly in the Americas. Partial sequences of the cytochrome c oxidase subunit 1 ( cox 1), ribosomal internal transcribed spacer region 2 (ITS2) and the large subunit 28S rDNA gene were obtained and analysed using pairwise distance matrices and parsimony methods in order to characterise the interrelationships between 14 isolates of four nominal species of Glypthelmins recognised on morphological grounds. The highest intra-specific sequence divergence occurred in the cox 1 (18.53%) sequence, followed by that of the ITS2 (5.44%) and 28S (4.63%). Genetic variability was detected between the three isolates originally identified as G. facioi Brenes et al., 1959 from two localities in Mexico and one locality in Costa Rica. Sequence divergence exhibited among these isolates ranged from 10.70 to 11.22%, from 0.48 to 0.97% and from 1.33 to 1.88% for cox 1, ITS2 and 28S, respectively. Phylogenetic analysis combining all three data-sets generated a single most parsimonious tree. The three isolates of G. facioi form a clade, with an isolate collected from frogs in Veracruz State as the sister group to an isolate from Tabasco State + G. facioi from Costa Rica. The information derived from pairwise distance of independent data-sets plus the phylogenetic information indicate that each of the two isolates from Mexico, identified a priori as G. facioi, represent separate species. A re-examination of specimens was carried out and a re-evaluation made of the morphological characters to find reliable differences that had been overlooked. As a consequence, G. brownorumae n. sp. from Tabasco and G. tuxtlasensis n. sp. from Veracruz are described based on molecular and morphological differences.

Haematoloechus danbrooksi n. sp. from the lungs of Rana vaillanti in Veracruz state, Mexico, was found. The new species is most similar morphologically to H. medioplexus, H. parviplexus, and H. meridionalis in having a ventral sucker less than half the diameter of the oral sucker. It differs from these species by the extension of the vitellaria, which are shorter in the new species, and in the shape of the tegumental spines, which are blunt in the new species. It differs from all other known species of Haematoloechus in the distribution of the uterine loops that are arranged diagonally and that present several short, extracecal. longitudinal loops in the postacetabular region. The new species shows 1.2% sequence divergence in partial 28S sequence with respect to H. medioplexus, 1.1% with H. parviplexus. and 2.5% with H. meridionalis, sequence divergences complementing the morphological differences.

A description is given of Perezitrema bychowskyi (Caballero & Caballero, 1975) based on newly collected specimens from the intestine of the tropical gar Atractosteus tropicus Gill in the Pantalos de Centla Biological Reserve, State of Tabasco, southeastern Mexico, collected in April 2001, and on a re-examination of the type-specimens. In contrast to the original description, the excretory vesicle of P. bychowskyi was found to be elongate saccular and the intestinal caeca join near the posterior extremity and open via a common median anus. These features, and the presence of a cirrus-sac, were found, using differential interference contrast optics in the type-specimens of P. viguerasi Barus & Moravec, 1967, the type-species of the genus. This made possible a re-diagnosis of Perezitrema Barus & Moravec, 1967. Although P. bychowskyi is very similar to P. viguerasi and their conspecificity cannot be excluded, the poor condition of the type-specimens of the latter does not enable their detailed comparison and, consequently, both are considered independent species for the time being. P. lepisostei (Watson, 1976) is considered a junior synonym of P. bychowskyi. Perezitrema is provisionally placed in the plagiorchioid family Macroderoididae, even though some of its morphological features are similar to those of the lepocreadioid families Enenteridae and Lepocreadiidae.

Margotrema guillerminae n. sp. is described from the cyprinid Hybopsis calientis and the goodeid Alloophorus robustus from Lake Zacapu, Michoacán State, in the Mesa Central of Mexico. The new species is easily distinguished from the only other species of the genus, M. bravoae, by having short ceca, extending posteriad to reach the region of the anterior testis, vitelline follicles that are mainly lateral to the ceca but with some intercecal (particularly at the ovarian region), and a seminal receptacle that is located immediately posterior to the ovary. Previous records of Urorchiinae gen. sp. and Margotrema sp. from Alloophorus robustus from Lake Pátzcuaro refer to M. bravoae, which appears to be specific to members of the Goodeidae.

A new species of Glypthelmins (Trematoda: Macroderoididae) is described from the intestine of Bufo marinus and Leptodactylus melanonotus from several localities of the Neotropical Region of Mexico. Glypthelmins poncedeleoni n. sp. can be differentiated from other species of the genus by having extracecally distributed vitellaria, ovary always larger than testes, and vitelline follicles grouped in 7 post-testicular, nonoverlapping, rosette-like clusters and 5 pretesticular overlapping clusters.

Salsuginus neotropicalis n. sp. is described from the gills of Belonesox belizanus (Kner), the pike killifish (Poeciliidae), from the southeastern Mexico. S. neotropicalis is distinguished from all other congeners by the morphology of the haptoral sclerites, especially by the presence of a ventral bar with notably enlarged ends, and by possessing overlapping gonads. The diagnosis of Salsuginus is amended based on the position of gonads in this species. This is the first known Salsuginus species occurring in a freshwater fish from the Neotropical Region.

An examination of three specimens of the Morelet's crocodile, Crocodylus moreletii Duméril et Bibron, from the Lagoon of Celestún, Yucatan, Mexico revealed the presence of the following eight helminth species: Acanthostomum americanum (Pérez Vigueras, 1956), Pelaezia loossi (Pérez Vigueras, 1956), Telorchis sp. juv., Pseudoneodiplostomum groschafti sp. n. (all trematodes), Dujardinascaris helicina (Molin, 1860), Contracaecum sp. Type 2 larvae, Micropleura sp. and Paratrichosoma recurvum (Solger, 1877) (all nematodes). Pseudoneodiplostomum groschafti sp. n. is established by indication based on the description of specimens from Crocodylus rhombifer from Cuba, given by Groschaft and Barus (1970). Acanthostomum acuti Caballero et Brennes, 1959 is considered a synonym of A. americanum. A. americanum and D. helicina are recorded for the first time from Mexico and Micropleura sp. is the first American representative of the genus recorded outside South America. Findings of A. americanum, Telorchis sp., P. groschafti, D. helicina and Micropleura sp. in C. moreletii represent new host records. Some observations on the early development of D. helicina are provided. All species, except for P. recurvum, are briefly described and illustrated and some problems concerning their morphology, taxonomy and geographical distribution are discussed.

Two new species of Calicotyle (Monocotylidae: Calicotylinae) are described from elasmobranchs in the western Gulf of California. Calicotyle californiensis n. sp. is described from a single specimen collected from a gray smoothhound shark (Mustelus californicus, Carcharhiniformes: Triakidae). It is distinguished from its congeners by the combination of having vaginal pores opening within the intercecal space, distal regions of the vaginae twisting, proximal regions of the vaginae fusing medially to form a kidney bean-shaped structure, and a relatively long male copulatory organ recurving 3 times and passing between the distal penis bulb and the seminal vesicle. Calicotyle urobati n. sp. is described from 16 specimens collected from at least the cloaca and rectum of the round rays Urobatis halleri and Urobatis maculatus (Rajiformes: Urolophidae). It is distinguished from its congeners by the combination of having vaginal pores opening outside the intercecal space and proximal regions of the vaginae terminating at the level of the ceca. Members of Calicotyle have not been reported previously from the eastern Pacific Ocean or from these hosts. In the past, species of Calicotyle have been distinguished based primarily on the shape and length of the male copulatory organ and hamuli. Divisions of the vaginae and the positions of the vaginal pores are also useful in distinguishing members of the genus.

Cicesetrema unami n. gen., n. sp. (Digenea: Cryptogonimidae) is described from the intestine of the California halibut, Paralichthys californicus, from San Quintin Bay, Baja California, Mexico. The new genus is distinguished from other members of the Cryptogoniminae in having vitellaria that form asymmetric bunches of follicles and extend in lateral fields from the level of the ovary posteriad beyond the testes. In addition, the species in the new genus possess a subterminal, funnel-shaped oral sucker that is prominent when protruded but usually retracted in a fold at the anterior end.

Molecular evidence is interpreted in the light of morphology to examine the validity of several species of Haematoloechus described as Mexican endemics. Internal transcribed spacers 1 and 2 and 28S ribosomal genes were sequenced for 11 isolates. Phylogenetic analysis of separate partitions and combined databases was conducted. Results were analyzed, in the light of morphological evidence. Haematoloechus macrorchis is proposed as a junior synonym of Haematoloechus longiplexus. Haematoloechus pulcher is a sibling species with Haematoloechus complexus in Lerma wetlands. In Mexico, Haematoloechus medioplexus is distributed along the east coast coinciding with the distribution of Rana berlandieri. The sister species of H. medioplexus is Haematoloechus coloradensis, sharing the distribution of the uterus as a synapomorphic character. Haematoloechus illimis is more closely related to H. medioplexus and H. coloradensis than to H. complexus. It can be distinguished by the distribution of the uterus, lobed ovary, and testes.

Monocotylid monogeneans were collected from the gills of 2 Rhinobatos productus and 5 Zapteryx exasperata in Bahia Almeja, Baja California Sur, Mexico. All are parasitized by monocotylids of the genus Spinuris, 9 specimens of Spinuris lophosoma Doran on Rhinobatos productus (new record) and 27 specimens of Spinuris zapterygis n. sp. on Z. exasperata. This new species differs from the other species in the genus Spinuris by the number of dorsal haptoral sclerites, morphology of hooks, and male copulatory apparatus. The generic diagnosis of the genus Spinuris is revised.

During a survey of the parasites of freshwater fishes from cenotes (sinkholes) of the Yucatan Peninsula the following species of monogeneans were found on cichlid, pimelodid, characid and poeciliid fishes: Sciadicleithrum mexicanum Kritsky, Vidal-Martinez et Rodriguez-Canul, 1994 from Cichlasoma urophthalmus (Günther) (type host), Cichlasoma friedrichsthali (Heckel), Cichlasoma octofasciatum (Regan), and Cichlasoma synspilum Hubbs, all new host records; Sciadicleithrum meekii Mendoza-Franco, Scholz et Vidal-Martínez, 1997 from Cichlasoma meeki (Brind); Urocleidoides chavarriai (Price, 1938) and Urocleidoides travassosi (Price, 1938) from Rhamdia guatemalensis (Günther); Urocleidoides costaricensis (Price et Bussing, 1967), Urocleidoides heteroancistrium (Price et Bussing, 1968), Urocleidoides anops Kritsky et Thatcher, 1974, Anacanthocotyle anacanthocotyle Kritsky et Fritts, 1970, and Gyrodactylus neotropicalis Kritsky et Fritts, 1970 from Astyanax fasciatus; and Gyrodactylus sp. from Gambusia yucatana Regan. Urocleidoides chavarriai, U. travassosi, U. costaricensis, U. heteroancistrium, U. anops, Anacanthocotyle anacanthocotyle and Gyrodactylus neotropicalis are reported from North America (Mexico) for the first time. These findings support the idea about the dispersion of freshwater fishes and their monogenean parasites from South America through Central America to southeastern Mexico, following the emergence of the Panamanian isthmus between 2 and 5 million years ago.

Creptotrema agonostomi n. sp. is described from the mugilid fish Agonostomus monticola from Río Cuitzmala, Jalisco, east México, from Río Las Palmas and Río Máquinas, Veracruz, west México, and from the ictalurid, Ictalurus balsanus from Río Chontalcoatlán, Guerrero, east México. It is distinguished from other species of Creptotrema by its small size, large acetabulum with vertical incision, cirrus sac not reaching the posterior border of acetabulum, and very small eggs, measuring 0.041-0.057 x 0.020-0.033 mm.

Campechetrema herrerai n. gen, n. sp. is described from the cichlid fish Petenia splendida from EI Vapor lagoon, an oligohaline lagoon, Campeche, México. It is distinguished from other genera of Cryptogoniminae by the presence of a single gonotyl, a preequatorial acetabulum, few vitelline follicles, and lack of pars prostatica and prepharynx.

Pseudorhabdosynochus yucatanensis sp. n. (Diplectanidae) is described from the gills of the red grouper, Epinephelus morio (Valenciennes, 1824) (Serranidae), from the coast of the Yucatan Peninsula, Mexico. This new species is characterized by having both the ventral and the dorsal squamodiscs composed of 10-12 rows of rods, with 0-1 innermost row forming a closed circle. Furthermore, the vagina of P. yucatanensis has a non-sclerotized ampulla with a fine, sclerotized duct leading to a sclerotized seminal receptacle. Prevalence (percentage of infected fish) and abundance (mean number of worms per examined fish) were estimated for P. yucatanensis from 8 localities along the coast of Yucatan. Prevalence varies from 38% to 100%, while abundance was between 1.2 +/- 0.6 and 43.2 +/- 17.8 worms per fish. The lack of linear relationship between the host length and the number of monogeneans per fish (regression F1,188 = 0.56, p = 0.45) was probably due to the fact that the sample was restricted to juvenile hosts.

Posthodiplostomum minimum adults were collected from natural hosts at Lake Pátzcuaro, Michoacán, México and from experimentally infected hosts. Intraspecific variation was measured using principal component analysis (PCA). Morphological traits such as general body shape, size, and the specific location of certain distinctive organs and structures showed great variation among hosts as described by PCA. These results extend previous studies on host-induced variation in P. minimum in showing that some conservative traits such as vitelline follicle distribution in fore-and hindbody, could be used for an extensive and complete revision of the genus Posthodiplostomum.

Examination of a total of 581 fish specimens of 15 species from 39 cenotes (sinkholes) in the Yucatan Peninsula, southeastern Mexico, revealed the presence of 10 species of adult trematodes. These were as follows: Saccocoelioides sogandaresi Lumsden, 1963, Saccocoelioides sp. (family Haploporidae), Cichlasotrema ujati Pineda et Andrade, 1989 (Angiodictyidae), Crassicutis cichlasomae Manter, 1936 (Homalometridae), Magnivitellinum simplex Kloss, 1966 (Macroderoididae), Stunkardiella minima (Stunkard, 1938) (Acanthostomidae), Oligogonotylus manteri Watson, 1976 (Cryptogonimidae), Genarchella tropica (Manter, 1936), G. astyanactis (Watson, 1976), and G. isabellae (Lamothe-Argumedo, 1977) (Derogenidae). Saccocoelioides sogandaresi is reported from Mexico for the first time. Poecilia velifera and P. latipunctata for S. sogandaresi, Cichlasoma octofasciatum for C. cichlasomae, Cichlasoma friedrichstahli and C. meeki for O. manteri, and C. meeki, C. octofasciatum and Gobiomorus dormitor for G. isabellae represent new host records. Most species found are described and figured and their host range and distribution are discussed.

Evaluation of comparative material, including type specimens, of 2 derogenid species (Digenea: Derogenidae) in freshwater fishes of the families Cichlidae and Pimelodidae in Mexico revealed the invalidity of Genarchella luistoddi (Jiménez, Guajardo, and Briseño, 1981), a parasite of cichlid fishes in northern Mexico. This taxon is considered to be conspecific with Genarchella isabellae (Lamothe-Argumedo, 1977), originally described from the pimelodid Rhamdia guatemalensis (Günther) and frequently occurring in cichlids of the genus Cichlasoma in southeastern Mexico.

Two stray dogs were found naturally infected with adult Alaria nasuae in Tamaulipas, Mexico. This is the first report of this species from a domestic dog, the first report of it from Mexico, and the first time the species has been recorded since its original description.