Systematic assessment of nymphs of Diesingiinae (Pentastomida: Sebekidae) parasitizing Palloceros harpagos (Cyprinodontiformes: Poeciliidae) from Parque Nacional Iguazú, Argentina: filling gaps in an incomplete phylogenetic framework.

During a search for parasites in fishes from Iguazu River, Argentina, a nymph of pentastomid was found encysted on mesenteries of Phalloceros harpagos. The 28S rDNA and COI mt-DNA were used to compare with the sequences deposited in the GenBank. Pentastomid nymphs belong to the subfamily Diesingiinae (Sebekidae) for having chloride cell pores distributed in a single row per annulus; also, the hooks and rows of spines of our material differ to other genera. Present specimens are most likely Diesingia sp., having 63-74 annuli, a U shaped oral cadre with fibers closing anteriorly and a peg like extension of the oral cadre. The 28S rDNA analysis places our samples into a sister group of Alofia sp., but the COI mt-DNA situate them on the base of the clade. In conclusion, our pentastomid positively belongs to Diesingia sp., however, indisputable assignation requires a reliable description of the nymph, or the availability of sequences linking nymphs and adults, which even could provide evidence of a new hitherto undescribed genus. Aditionally, the systematic position of Sebekia oxycephala previously described by P. harpagos is discussed on the basis of our results, allowing us to suggest a re-assignation of such specimens to the genus Diesingia.

Comparative exploration of the morphological plasticity of Trichodina centrostrigeata (Peritrichia: Mobilida), ectoparasite from the gills of two tilapia species (Oreochromis niloticus and O. mossambicus) in a global context.

Trichodina centrostrigeata Basson, Van As et Paperna, 1983 from Oreochromis mossambicus (Peters) and O. niloticus (Linnaeus) from different host populations from Argentina, Mexico and South Africa was reviewed. Although T. centrostrigeata has a distinct denticle structure that makes morphological taxonomic inferences uncomplicated, variation of the denticles within and among individuals and populations were still observed. While traditional taxonomy of mobilines is heavily reliant on morphometrics, and recently even more so on molecular analysis, this paper proposes the use of geometric morphometry, specifically elliptical Fourier analysis, to address morphological conflicts that arise when comparing different populations. By applying this technique, combined with traditional taxonomy, it was found that T. centrostrigeata in this study can be grouped into two separate morphotypes, the first (type a) from aquaculture farms in Argentina and Mexico and the second (type b) from a natural habitat in Glen Alpine Dam, South Africa. This study supports the validity of geometric morphometry as an additional technique to distinguish not only between species but also evolutionary plasticity of the same species from different localities and habitats.

New morphological and molecular data for Xystretrum solidum (Gorgoderidae, Gorgoderinae) from Sphoeroides testudineus (Tetraodontiformes, Tetraodontidae) in Mexican waters.

Adults of trematodes in the genus Xystretrum Linton, 1910 (Gorgoderidae, Gorgoderinae) are parasites found exclusively in the urinary bladders of tetraodontiform fishes. However, limited and unclear morphological data were used to describe the type species, X. solidum Linton, 1910. Here, we present the first detailed morphological information for a member of Xystretrum. Morphological characters were described using light and scanning electron microscopy (SEM) of Xystretrum specimens from Sphoeroides testudineus (Linnaeus) (Tetraodontiformes, Tetraodontidae), collected at six localities off the northern Yucatan Peninsula coast of the Gulf of Mexico. We also compared sequence fragments of the 28S (region D1-D3) ribosomal DNA and mitochondrial Cytochrome c oxidase subunit 1 (COI) gene with those available for other gorgoderine taxa. We assigned these Xystretrum specimens to X. solidum, despite the incompleteness of published descriptions. The data provide a foundation for future work to validate the identities of X. solidum, X. papillosum Linton, 1910 and X. pulchrum (Travassos, 1920) with new collections from the type localities and hosts. Comparisons of 28S and COI regions described here also provide an opportunity to evaluate the monophyletic status of Xystretrum.

A checklist of trichodinid species (Ciliophora: Trichodinidae) on tilapia fishes (Cichlidae), with new records from Mexico and the first data from Argentina.

Tilapia is the common name for a wide spectrum of cichlid fishes usually selected for aquaculture activities. However, some aspects of the natural history of these fishes, such as the diversity of certain ectoparasitic protistan groups remain understudied. In order to understand the diversity of ciliates of the family Trichodinidae parasitizing tilapia around the world, a database with all available accounts was assembled. This information, along with records derived from our own recent research, allowed us to generate a checklist containing all the records for tilapia-Trichodinidae associations. The checklist is presented as a host-parasite list containing 44 nominal taxa from 29 countries on four continents, and it also presents the first data from Argentina, where tilapia culture is still an incipient, but growing activity. The observed high species richness of trichodinids is probably derived from a set of specific taxa for tilapia, along with an important component of species acquired from the new environments where tilapia have been introduced. Data presented here could be used along with existing information of metazoan parasites to build a general view about diseases that affect tilapia.

Taxonomic status of Rhabdochona ictaluri (Nematoda: Rhabdochonidae) based on molecular and morphological evidence.

The genus Rhabdochona includes more than 100 species infecting freshwater fishes in all zoogeographical regions of the world. In Mexico, 12 nominal species of Rhabdochona have been recorded. Of these, Rhabdochona ictaluri was originally described as a parasite of endemic catfishes of the family Ictaluridae; however, the species was later considered on morphological grounds as a junior synonym of Rhabdochona kidderi. In this study, newly sampled specimens of R. ictaluri were obtained from the type host and type locality and were used to perform a detailed morphological analysis and molecular phylogenetic inferences through one mitochondrial and two nuclear genes; data were used in an integrative taxonomy context to test the taxonomic status of R. ictaluri. This approach proved to be very useful to confirm the validity of this species, and robust species limits were established between these two putative species considering morphology, molecular data, host association, and biogeography.

A checklist of ciliate parasites (Ciliophora) of fishes from Mexico.

A database with all available published accounts of the ciliate parasite species of Mexican fishes was assembled. This information, along with records derived from own recent research, allow generating a checklist containing all the records, which is a necessary first step to address future questions in the areas of ecology, evolutionary biology and biogeography of these host-parasite associations. The checklist is presented as a parasite-host list, and a host-parasite list. The checklist contains 30 nominal species, from 9 genera and 8 families of ciliate parasites. Most of the primary records were done for exotic fish species, artificially introduced to Mexico for aquaculture purposes; however, recent works have been conducted in diverse species of native fishes. Excepting one, all the ciliate species listed here have been previously recorded for diverse fish species from different localities around the world. Based on the amount of information contained in this checklist, much more effort is necessary to accurately know the diversity of species of this type of parasites in fish fauna of Mexico.

Checklist of helminth parasites of Goodeinae (Osteichthyes: Cyprinodontiformes: Goodeidae), an endemic subfamily of freshwater fishes from Mexico.

From August 2008 to July 2010, 1,471 fish belonging to the subfamily Goodeinae (representing 28 species) were collected from 47 localities across central Mexico and analyzed for helminth parasites. In addition, a database with all available published accounts of the helminth parasite fauna of goodeines was assembled. Based on both sources of information, a checklist containing all the records was compiled as a necessary first step to address future questions in the areas of ecology, evolutionary biology and biogeography of this host-parasite association. The checklist is presented in two tables, a parasite-host list and a host-parasite list. The checklist contains 51 nominal species, from 34 genera and 26 families of helminth parasites. It includes 8 species of adult digeneans, 9 metacercarie, 6 monogeneans, 3 adult cestodes, 9 metacestodes, 1 adult acanthocephalan, 1 cystacanth, 6 adult nematodes and 8 larval nematodes. Based on the amount of information contained in the checklist, we pose that goodeines, a subfamily of viviparous freshwater fishes endemic to central Mexico, might be regarded as the first group of wildlife vertebrate for which a complete inventory of their helminth parasite fauna has been completed.

Helminth parasites of freshwater fishes from Cuatro Ciénegas, Coahuila, in the Chihuahuan Desert of Mexico: inventory and biogeographical implications.

As part of an ongoing inventory of the helminth parasites of freshwater fishes in Mexico, 570 individual fish were collected between Apr 2008 and Oct 2011 in 26 localities along the Cuatro Ciénegas region in Coahuila State, northern Mexico. Seventeen species of hosts, mostly corresponding to Nearctic freshwater elements, were studied. A total of 8324 individual worms were collected during this survey, representing 25 species of helminths, of which 9 were digeneans, 3 monogeneans, 3 acanthocephalans, 9 nematodes and 1 cestode. Most of the records in this checklist represent new host or locality records. The information provided in this checklist may be helpful for our understanding of the biodiversity and historical biogeography of this host-parasite system, because in the Cuatro Ciénegas region occur a Nearctic freshwater fish fauna, along with Neotropical and endemic elements, and from a biogeographical point of view, this may represent a transitional area.

Helminth parasites of Xenotaenia resolanae (Osteichthyes: Cyprinodontiformes: Goodeidae) from the Cuzalapa hydrological system, Jalisco, Mexico.

Six helminth species were recorded during the helminthological examination of 35 specimens of the goodeid Xenotaenia resolanae from Arroyo Durazno, Jalisco, Mexico, a tributary of the Cuzalapa River. Helminth species identified included: 4 species of digeneans, i.e., Posthodiplostomum minimum (metacercariae), Clinostomum companatum (metacercariae), Dendrorchis sp. (adult), and Margotrema guillerminae (adult); and 2 species of nematodes, i.e., Spiroxys sp. (larvae) and Rhabdochona ahuehuellensis (adult). A very low number of individual larvae were found. The observed species richness, individual parasite abundance, and diversity were low at both component community and infracommunity levels. The values of similarity between infracommunities were relatively high because of the predominance of the digenean M. guillerminae, the species that reached the higher values of both prevalence and abundance. High water flow of the collecting site is suggested as the main factor determining the depauperate helminth assemblage in this fish species.

Diversidad de helmintos parásitos de peces dulceacuícolas en dos cuencas hidrológicas de México: los helmintos y la hipótesis del México betadiverso / Diversity of freshwater fishes parasitic helminths in two Mexican hydrological basins: helminths of the hypothesys betadiverse Mexico

Se analizó la diversidad de helmintos parásitos de peces dulceacuícolas en distintas unidades geográficas dentro de dos de las cuencas hidrológicas más importantes de México, río Lerma y río Papaloapan, con la finalidad de establecer la tasa de recambio entre unidades y determinar cómo contribuye la diversidad de cada región a la hipótesis del México betadiverso. A cada cuenca hidrológica se le sobrepuso una gradilla de 0,5×0,5º y se tomaron en cuenta aquellos cuadros en los que existe al menos una localidad con registro de helmintos de peces. Con base en riqueza de especies en cada cuadro, se calculó la diversidad beta de la cuenca hidrológica utilizando la formula b= Sg/Sa. Adicionalmente se calculó un índice de complementariedad para determinar cuán disímiles son entre sí los cuadros de cada cuenca y cuán diferentes son las cuencas entre sí en cuanto a su composición de especies. El total de especies de helmintos parásitos de las cuencas analizadas resultó contenido en nueve cuadros, cinco localizados en la cuenca del Papaloapan y cuatro en la del río Lerma. De manera similar a algunos estudios dirigidos a establecer áreas de conservación, las áreas complementarias obtenidas pueden ser consideradas como relevantes debido a que en éstos cuadros existen localidades que mantienen una calidad ambiental suficiente para que en ellas puedan completarse los ciclos de vida complejos de la mayor parte de los helmintos seleccionados para este estudio

Atactorhynchus duranguensis n. sp. (Acanthocephala: Atactorhynchinae) from Cyprinodon meeki (Pisces: Cyprinodontidae) near Durango, Mexico.

Atactorhynchus duranguensis n. sp. (Acanthocephala: Atactorhynchinae) is described from the intestine of Cyprinodon meeki Miller, an endemic freshwater fish from a far-inland locality of Mexico. Diagnostic features include: body small, stout, ventrally curved; small cylindrical proboscis armed with 16 alternating vertical rows of four or five hooks; anterior two or three hooks conspicuous, stout and larger than other hooks, and have large, rod-shaped roots with a markedly and abruptly enlarged base; three posterior hooks of each row are smaller and rootless; single-walled proboscis receptacle; lemnisci equal in length, elongate and robust; and cement gland syncytial, larger than testis. The new species is smaller than A. verecundus Chandler, 1935, the only previously described species in the genus. The shape of the proboscis of the new species is strikingly different from that of A. verecundus, which is widest at the apex. Likewise, the greatest width of the trunk of the new species is in about the middle, differing from that of A. verecundus where the trunk is widest posteriorly. The new species also can be distinguished from A. verecundus because of its much smaller hook lengths and slightly smaller proboscis. In addition, the proportion of large apical proboscis hooks in relation to the small basal hooks is different: the basal hooks of A. verecundus are about half the size of the anterior hooks and but only about a quarter of the size in A. duranguensis. Unlike A. verecundus, the base of the roots are markedly and abruptly enlarged in the new species. Finally, the eggs of the new species are smaller (23-27 x 8-10 microm) than those of A. verecundus (27-30 x 12-13 microm).

Helminth parasites in freshwater fish from the Papaloapan river basin, Mexico.

A checklist based on previously published records and original data is presented for the helminth parasites reported in 35 fish species from nine families from the Rio Papaloapan basin, east Mexico. The checklist contains 85 taxa from 39 helminth families. Trematodes and nematodes were the most abundant taxonomic groups. The helminth fauna in the fish of the Papaloapan River basin predominantly consists of Neotropical species that are largely autogenic. The introduced species Centrocestus formosanus was the most widely distributed helminth, infecting 16 host species. Ten of the recorded helminth species have only been found in fish from the Papaloapan. This inventory contributes 157 new host records, and reports the presence of 30 helminth species in the Papaloapan for the first time . This inventory shows the richness of helminth parasite species in the fish of the Papaloapan River basin in comparison with the other hydrological basins in Mexico. It also demonstrates that this fauna is typically Neotropical and quite similar to that from the neighboring basins of the Grijalva-Usumacinta system and the Yucatan Peninsula. The data also suggest highly effective transmission between environments within the same basin and that the regional parasite fauna is strongly influenced by fish community composition.

Helminth parasites of Chapalichthys encaustus (Pisces: Goodeidae), an endemic freshwater fish from Lake Chapala, Jalisco, Mexico.

A total of 6 helminth species were recorded during helminthological examination of 50 Chapalichthys encaustus from Lake Chapala, Jalisco, Mexico. Helminth species identified included: Salsuginus sp. (an undescribed monogenea); Posthodiplostomum minimum (metacercariae); Cyclustera ralli (metacestode); Polymorphus brevis (cystacanth); Contracaecum sp. (nematode larvae); and Rhabdochona lichtenfelsi (adult nematode). Of these, 2 (Salsuginus sp. and R. lichtenfelsi) are specialist species. The observed species richness, individual parasite abundance, and diversity were low. Data suggest that host specificity is an important factor contributing to observed community composition and richness. Host feeding habits and helminth species availability seem to determine the characteristics of these helminth assemblages.

Helminth parasites of the tropical gar, Atractosteus tropicus Gill, from Tabasco, Mexico.

A total of 8 helminth species were recorded in an examination of 43 tropical gar, Atractosteus tropicus Gill, collected at the Pantanos de Centla Biosphere Reserve, Tabasco, Mexico. The parasite species included 1 adult trematode, 3 metacercariae, 1 cestode, 1 adult nematode, and 2 nematode larvae. Six of these 8 species were rare, with low prevalence (< 17%) and abundance (< 1.0 helminths per examined fish). The larvae of Contracaecum sp. were the most abundant in the sample, constituting 60% of the total helminths (64% prevalence, 3.8 +/- 5.2 abundance), followed by the cestode Proteocephalus singularis, constituting 18% of the worms (30.5% prevalence, 1.1 +/- 3.0 abundance). Species richness, individual parasite abundance, and diversity were low in the infracommunities. The recording of 3 specialist species in the tropical gar confirms that the helminth fauna of gar has an appreciable degree of specificity. This study indicates the importance of ecological determinants of richness in helminth communities of the tropical gar.

Rhabdochona guerreroensis n. sp. (Nematoda: Rhabdochonidae) from the intestine of the gobiid Sicydium multipunctatum from fresh waters in Mexico.

Rhabdochona guerreroensis n. sp. is described on the basis of specimens recovered from the intestine of Sicydium multipunctatum (Regan) (Gobiidae, Perciformes) from 2 localities in Mexico. This species is characterized by 12 teeth in the prostom (occasionally 11), asymmetrical numbers of postanal papillae, a broad distal tip of the larger (left) spicule with a small bifurcation covered by narrow cuticular membrane, a smaller (right) spicule with a dorsal barb on its distal tip, and filamented eggs.

Neophilometroides n. gen. (Nematoda: Philometridae) for Philometroides caudatus Moravec, Scholz and Vivas-Rodríguez, 1995, with erection of Neophilometroidinae n. subfam.

A detailed examination (including scanning electron microscopy) of newly collected nematode specimens (subgravid females) referable to Philometroides caudatus Moravec, Scholz and Vivas-Rodríguez, 1995, from the swimbladder of the pimelodid catfish, Rhamdia guatemalensis, in the Papaloapan River in Tlacotalpan, State of Veracruz, Mexico, as well as the paratype specimens of this species, revealed the presence of a small buccal capsule armed with peribuccal teeth in the female. Because of this unique morphological feature within the Philometridae, and considering other taxonomically important characters such as the structure of the male tail and the shape of the anterior end of the esophagus in the gravid female, Neophilometroidinae n. subfam, and Neophilometroides n. gen. are proposed to accommodate this species. Philometra paraguayensis Petter, 1995, is transferred to Neophilometroides as N. paraguayensis (Petter, 1995) n. comb. Newly collected specimens are briefly described and illustrated.

Two new nematodes, Paraseuratoides ophisterni gen. et sp. n. (Quimperiidae) and Philometra ophisterni sp. n. (Philometridae), from the swamp-eel Ophisternon aenigmaticum in Mexico.

Two new nematodes, Paraseuratoides ophisterni gen. et sp. n. (Seuratoidea: Quimperiidae) and Philometra ophisterni sp. n. (Dracunculoidea: Philometridae) are described based on specimens recovered from the intestine and mesentery, respectively, of the swamp-eel Ophisternon aenigmaticum Rosen et Greenwood (Synbranchiformes: Synbranchidae) from a canal of the Papaloapan River in Tlacotalpan, State of Veracruz, Mexico. The genus Paraseuratoides is mot similar to Paraseuratum Johnston et Mawson, 1940, differing from it mainly in the absence of a bulbous inflation on the anterior end of the oesophagus and in the structure of the mouth (presence of 6 spines in addition to 6 oesophageal teeth). Neoquimperia Wang, Zhao, Wang et Zhang, 1979 and Wuinema Yu et Wang, 1992 are synonymised with Ezonema Boyce, 1971 and Paragendria Baylis, 1939, respectively, and Haplonema hamulatum Moulton, 1931 is considered a junior synonym of Ichthyobronema conoura Gnedina et Savina, 1930. Philometra ophisterni (only females) is mainly characterised by minute cephalic papillae, a greatly developed anterior oesophageal bulb separated from the cylindrical part of the oesophagus, anterior extension of the oesophageal gland anterior to the nerve ring, and by the character of large caudal projections. This is the first Philometra species recorded from inland fishes in Mexico.