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The phylogenetic position of Clinostomum heluans Braun, 1899 within the genus Clinostomum Leidy, 1856 is reported in this study based on sequences of the barcoding region of the mitochondrial cytochrome c oxidase subunit 1 gene ( COX1). Additionally, molecular data are used to link the adult and the metacercariae of the species. The metacercariae of C. heluans were found encysted infecting the cichlid fish Australoheros sp. in Minas Gerais, Brazil, whereas the adults were obtained from the mouth cavity of the Great White Egret, Ardea alba, in Campeche, Mexico. The COX1 sequences obtained for the Mexican clinostomes and the Brazilian metacercaria were almost identical (0.2% molecular divergence), indicating conspecificity. Similar molecular divergence (0.2-0.4%) was found between sequences of C. heluans reported here and Clinostomum sp. 6 previously obtained from a metacercaria recovered from the cichlid Cichlasoma boliviense in Santa Cruz, Bolivia. Both maximum likelihood and Bayesian inference analyses unequivocally showed the conspecificity between C. heluans and Clinostomum sp. 6, which form a monophyletic clade with high nodal support and very low genetic divergence. Moreover, tree topology reveals that C. heluans occupies a basal position with respect to New World species of Clinostomum, although a denser taxon sampling of species within the genus is further required. The metacercaria of C. heluans seems to be specific to cichlid fish because both samples from South America were recovered from species of this fish family, although not closely related. [ABSTRACT FROM AUTHOR]

Adults of the genus Austrodiplostomum are parasites in cormorants of the New World, whereas metacercariae are parasites from eye globe and brain of freshwater and brackish water fishes. In this study, specimens of Austrodiplostomum mordax from South America (type-species) were analyzed together with other specimens of Austrodiplostomum spp. collected from several locations across Middle America and North America. Partial DNA sequences of the mitochondrial gene cytochrome c oxidase subunit I ( COI), the internal transcribed spacers ( ITS1, ITS2, and 5.8S gene), and the D2-D3, domains of the large subunit ( LSU) of nuclear ribosomal DNA, were generated for both developmental stages and compared with available sequences of Austrodiplostomum spp. Phylogenetic analyses inferred with each molecular marker using maximum likelihood and Bayesian inference revealed the existence of 4 lineages representing 2 described species, A. mordax and Austrodiplostomum compactum (syn. Austrodiplostomum ostrowskiae) and 2 undescribed species of Austrodiplostomum recognized in previous studies. The COI haplotype network inferred with 172 sequences detected 28 haplotypes divided into 4 clusters, separating each other by 33 and 40 substitutions and with a genetic divergence ranging from 9 to 12%. The largest group included specimens identified as A. compactum plus those identified as A. ostrowskiae, supporting the synonymy of both species. As a result, we conclude that A. compactum is widely distributed across the Americas, in locations of the United States, Mexico, El Salvador, Honduras, Costa Rica, Venezuela, Peru, and Brazil. The other 2 undescribed species of the genus Austrodiplostomum were previously recorded in the United States and now are reported in Mexico. These 2 species cannot be described because adult forms have not been found in their definitive hosts. Finally, the species A. mordax has been found only in some lakes from Argentina, and it was validated in this study through molecular analyses.

This study investigates the systematic position of some species of the genus Saccocoelioides Szidat, 1954, and the species Culuwiya cichlidorum Aguirre-Macedo and Scholz, 2005 , from North and Middle America using new morphological data and partial sequences of 2 nuclear genes, the large subunit and the internal transcribed spacer 2 from ribosomal DNA. In total 74 specimens representing 4 species of Saccocoelioides (41 of Saccocoelioides sogandaresi, 3 of Saccocoelioides chauhani, 6 of Saccocoelioides lamothei, and 12 of Saccocoelioides olmecae) plus 12 specimens of Culuwiya cichlidorum were analyzed. The phylogenetic analyses inferred with maximum likelihood method and Bayesian inference showed that the 4 species of Saccocoelioides formed a clade divided into 4 subclades representing each species. In addition, 7 specimens sequenced from the type host and locality of Culuwiya cichlidorum were nested in 2 clades: the first clade with specimens of C. cichlidorum from Costa Rica, and the second clade with specimens of S. sogandaresi from Mexico, Honduras, Nicaragua, and Costa Rica. Our analyses suggest that C. cichlidorum should be reallocated into Saccocoelioides, as was originally designated Saccocoelioides cichlidorum n. comb., is restricted to Nicaragua and Costa Rica and associated with cichlid fishes. In contrast, the specimens identified previously as Culuwiya cichlidorum from the coast of Gulf of Mexico by Aguirre-Macedo and Scholz belong to S. sogandaresi, which has a wide distribution that extends from Galveston Bay (U.S.A.) in Gulf of Mexico to Atlantic and Pacific slopes associated with poeciliid and cichlid fishes. New morphological data derived from scanning electron microscopy photographs of the body surface show a characteristic pattern of spination that is useful to distinguish between S. cichlidorum n. comb. and S. sogandaresi.

This study investigates the systematics of Paracreptotrema Choudhury, Pérez-Ponce de León, Brooks and Daverdin, 2006 using morphological data (stained whole mounts and scanning electron microscopy) and partial sequences of the 28S ribosomal rRNA gene, obtained from freshly collected material. In total, 484 specimens representing 4 species, i.e., Paracreptotrema blancoi (157), Paracreptotrema profundulusi (12), Paracreptotrema rosenthali (8), and Paracreptotrema blancoi sensu Salgado-Maldonado et al. (2011) (307) were collected. Existing museum depositions were also studied. The 28S rRNA gene sequences of these Paracreptotrema spp. were aligned, along with sequences from 22 other allocreadiids and 4 other non-allocreadiid xiphidiatan species. Bayesian inference and maximum likelihood analyses indicated a paraphyletic Paracreptotrema split into 3 clades: 1 comprising P. blancoi and P. rosenthali that was sister to a clade formed by 3 other species of allocreadiids (species of Wallinia, Creptotrematina, and Auriculostoma) typically found in characid fishes, a second clade formed solely by Paracreptotrema heterandriae as the sister taxon of the aforementioned species, and a third by P. profundulusi and specimens erroneously identified as P. blancoi. Two new taxa were erected to reflect these results: Paracreptotrematoides for Paracreptotrema heterandriae, and Pseudoparacreptotrema for Paracreptotrema profundulusi and P. macroacetabulata (the species erroneously identified as P. blancoi from profundulids across Middle America). Closer consideration of the morphology corroborates these findings. The revised systematics also indicated that Paracreptotrema spp. are found in poeciliids, whereas Pseudoparacreptotrema spp. parasitize profundulids. The study demonstrates the value of an integrative taxonomy approach to address the apparently complicated systematics of the allocreadiids.

Gyrodactylid population growth may depend on abiotic variables such as temperature. We tested the survival and reproductive rate of Gyrodactylus mexicanus, a parasite infecting fins of Girardinichthys multiradiatus, at 3 different water temperatures, 10-13, 19-22, and 24 C. The temporal sequence of birth and age at death of each parasite isolated from the hosts was recorded through at least 8 generations. Our results showed that the average number of offspring per parasite was 2.0 when averaged across all temperatures. However, the generation time was negatively correlated with temperature. The innate capacity for increase (r(m)) was positively correlated with water temperature: from 0.29 parasite/day at 13 C to 0.48 parasite/day at 24 C. These data confirm that water temperature has a direct influence on parasite population dynamics. The current study represents the first contribution to understanding the population ecology of the monogenean G. mexicanus in central Mexico.

Species of Floridosentis (Acanthocephala) are common parasites of mullets (Mugil spp., Mugilidae) found in tropical marine and brackish water in the Americas. Floridosentis includes 2 species distributed in Mexico, i.e., Floridosentis pacifica, restricted to the Pacific Ocean near Salina Cruz, Oaxaca, and Floridosentis mugilis, distributed along the coast of the Pacific Ocean and the Gulf of Mexico. We sampled 18 populations of F. mugilis and F. pacifica (12 from the Pacific and 6 from the Gulf of Mexico) and sequenced a fragment of the rDNA large subunit to evaluate phylogenetic relationships of populations of Floridosentis spp. from Mexico. Species identification of museum specimens of F. mugilis from the Pacific Ocean was confirmed by examination of morphology traits. Phylogenetic trees inferred with maximum parsimony, maximum likelihood, and Bayesian inference indicate that Floridosentis is monophyletic comprising of 2 major well-supported clades, the first clade corresponding to F. mugilis from the Gulf of Mexico, and the second to F. pacifica from the Pacific Ocean. Genetic divergence between species ranged from 7.68 to 8.60%. Intraspecific divergence ranged from 0.14 to 0.86% for F. mugilis and from 1.72 to 4.49% for F. pacifica. Data obtained from diagnostic characters indicate that specimens from the Pacific Ocean in Mexico have differences in some traits among locations. These results are consistent with the phylogenetic hypothesis, indicating that F. pacifica is distributed in the Pacific Ocean in Mexico with 3 major lineages.

The genus Southwellina is composed of 3 described species, i.e., S. hispida (the type species), S. dimorpha, and S. macracanthus. All 3 are endoparasites of fish-eating birds that have worldwide distributions. Morphologically, the genus is characterized by possessing a short and compact trunk, 2 fields of spines in the anterior region of the trunk (in at least 1 sex), a short cylindrical proboscis (sometimes with a swollen region armed with numerous longitudinal rows of hooks), a double-walled proboscis receptacle, and 4 tubular cement glands in males. In the current study, specimens identified as S. dimorpha were collected from Eudocimus albus (white ibis), the type host from the Gulf of Mexico. Sequences of 2 nuclear genes (small subunit [SSU] and long subunit [LSU] ribosomal DNA) and 1 mitochondrial gene (cytochrome c oxidase subunit 1 [cox 1]) of S. dimorpha and S. hispida were obtained and used to reconstruct the phylogenetic relationships of both species with respect to published sequences of 11 species representing 6 genera of Polymorphidae. Maximum parsimony (MP) and maximum likelihood (ML) analyses of the concatenated data set (SSU + LSU + cox 1) were identical in depicting Southwellina as paraphyletic, indicating that the genus should be revised. The MP and ML trees identified S. hispida as a sister to Polymorphus brevis, whereas S. dimorpha was a sister to Hexaglandula corynosoma. Morphologically, S. dimorpha is distinct from H. corynosoma, which is characterized by a short trunk with 1 field of spines in the anterior part of the trunk in both genders, and males with 6 tubular cement glands. The genetic divergence estimated from a concatenated data set between 2 isolates of S. hispida and S. dimorpha ranged from 10.7 to 11.0%. This range of genetic divergence is similar to that found among other genera of Polymorphidae, which extends from 6.0 to 12.0%. Southwellina dimorpha differs from S. hispida in the shape of the proboscis and the presence of 1 field of spines (S. dimorpha) versus 2 fields (S. hispida) on the anterior region of the trunk in females. Based on the phylogenetic position of S. dimorpha within Polymorphidae, coupled with levels of genetic divergence and, more importantly, the morphological and ecological (host specificity) differences, we propose the erection of a new genus to accommodate S. dimorpha.

Neoechinorhynchus golvani is an intestinal parasite of freshwater and brackish water fishes distributed in Mexico. The genetic variability of 40 samples representing 12 populations from north, south, and central Mexico, and 1 from Costa Rica, was estimated by sequencing 2 nuclear genes (ITS1, 5.8S, ITS2, and LSU rDNA, including the domain D2 + D3). The length of both genes ranged from 700 to 779 base pairs (bp) and from 813 to 821 bp, for ITSs and LSU, respectively. The genetic divergence among populations ranged from 19.5 to 35.3% with ITSs and from 9.28 to 19.58% with LSU. Maximum likelihood and maximum parsimony analyses were performed for each data set and also for 2 combined data sets (ITSs + LSU rDNA with and without outgroups), showing strong similarities among trees, with high bootstrap support in all cases. Genetic divergence, in combination with phylogenetic analyses, suggested that the acanthocephalan N. golvani represents a complex of cryptic species, which is composed of at least 3 lineages. The first lineage, corresponding with N. golvani, shows a wide distribution, including localities from northeastern Mexico, southwards through central and southeastern Mexico, and further down to Costa Rica. This lineage is associated with cichlid fishes in strictly freshwater environments. Lineages 2 and 3 are distributed in brackish water systems along the Gulf of Mexico and Pacific slopes, respectively; both are associated with eleotrid fishes, and apparently represent 2 cryptic species. The diversification of the eleotrid and cichlid lineages seems to be the result of independent host-switching events from the ancestral population.

Species of Pseudocorynosoma are North and South American acanthocephalans that use waterfowl as definitive hosts and amphipods as intermediate hosts, whereas species of Andracantha occur in fish-eating birds with a worldwide distribution. Pseudocorynosoma and Andracantha were originally described as Corynosoma (now restricted to endoparasites of marine mammals). Morphologically, Andracantha is distinct from other genera of Polymorphidae in possessing 2 fields of spines on the trunk, whereas Corynosoma and Pseudocorynosoma have a single field. A recent phylogenetic hypothesis based on morphological characters suggested that Andracantha is closely related to Corynosoma, whereas Pseudocorynosoma was of uncertain phylogenetic position within the Polymorphidae. To test the systematic affinities of these 3 genera, we sequenced 2 nuclear genes (SSU and LSU ribosomal DNA) and 1 mitochondrial gene (cytochrome c oxidase subunit 1; cox 1) of species representing Corynosoma, Andracantha, and Pseudocorynosoma and analyzed the data, including available sequences of other polymorphids. Maximum parsimony (MP), maximum likelihood (ML), and Bayesian analyses of the combined (SSU + LSU) sequences and the concatenated data of 3 genes (SSU + LSU + cox 1) placed Andracantha as the sister taxon to Corynosoma with robust support values. All analyses also showed that Pseudocorynosoma is an independent lineage that does not share a common ancestry with Andracantha and Corynosoma. These phylogenetic hypotheses suggest that birds were the ancestral hosts of polymorphids and that the association of Corynosoma with marine mammals represents a subsequent episode of colonization.

The systematic relationships of acanthocephalans, including Leptorhynchoides and Pseudoleptorhynchoides that occur in freshwater and marine fishes in Neartic and Neotropical regions, are enigmatic. Leptorhynchoides (3 species) and Pseudoleptorhynchoides (1 species) are presently classified in the Rhadinorhynchidae. However, recent molecular and morphological phylogenies have challenged the monophyly of this family. Sequences of nuclear ribosomal DNA (large subunit, small subunit regions) and the mitochondrial cytochrome c oxidase subunit I gene of Leptorhynchoides thecatus and Pseudoleptorhynchoides lamothei were used in phylogenetic analyses with available sequences of 26 other acanthocephalans. Maximum parsimony and maximum likelihood analyses were identical in placing both genera in the Illiosentidae. Bootstrap analyses also indicate that placement of these genera with members of Illiosentidae is reliably supported.

Members of the Polymorphidae (Acanthocephala) are distributed worldwide as endoparasites of marine mammals, fish-eating birds, and waterfowl. The family contains 10 genera, with approximately 127 species. Polymorphids are characterized by having a spinose trunk with a bulbous proboscis, double-walled proboscis receptacle, long lemnisci, and 4 tubular cement glands. The taxonomic position of several genera within Polymorphidae has been controversial when considering morphological and ecological characters. The mitochondrial coding gene cytochrome-c oxidase representing species of 5 genera of polymorphids (Corynosoma, Lühe, 1904, Hexaglandula Petrochenko, 1950, Southwellina Witenberg 1932, Polymorphus Luhë, 1911, and Profilicollis Meyer, 1931) were sequenced to determine the sister-group relationships among 2 particular genera, i.e., Hexaglandula, and Profilicollis. Maximum likelihood and Bayesian analyses showed that Polymorphidae is a monophyletic assemblage, and that 3 major clades are present. Our results provide support for the idea that Hexaglandula represents an independent lineage, whereas, in the case of Profilicollis, there is no conclusive evidence that they are not members of Polymorphus. The analyses also confirm that Polymorphus is paraphyletic, suggesting that the genus represents a complex of species that should be reexamined and reclassified using morphological, ecological, and molecular data. Our observations suggest that decapods (intermediate hosts for the 2 genera under study) were independently colonized at least twice during the evolutionary history of the group.

The Palaeacanthocephala is traditionally represented by 2 orders, Echinorhynchida and Polymorphida, with 10 and 3 families, respectively. To test the monophyly of the class, these 2 orders, and certain families, phylogenies were inferred using nuclear small-subunit (SSU) and large-subunit (LSU) ribosomal DNA sequences obtained for 29 species representing 10 families, 2 other classes of acanthocephalans, and 3 rotifer outgroups. Phylogenetic relationships were inferred by analyzing combined SSU and LSU sequences using maximum parsimony (MP) and maximum likelihood (ML) methods. Parsimony and ML trees inferred from combined analysis of these rDNA data strongly supported monophyly of Palaeacanthocephala and provided good resolution among species. Neither Polymorphida nor Echinorhynchida was monophyletic. Gorgorhynchoides bullocki (Echinorhynchida) was nested within the 6 species representing Polymorphida, and this clade was nested within species representing Echinorhynchida. Three of 4 palaeacanthocephalan families that could be evaluated were not monophyletic, and this finding was strongly supported. These results indicate that the family level classification of palaeacanthocephalans, which is mainly based on combinations of shared characters (not shared derived characters), needs to be reevaluated with respect to comprehensively sampled phylogenetic hypotheses.

Species of Corynosoma (Acanthocephala) are distributed worldwide as parasites of marine mammals and sea birds. Species diagnosis is based on morphological characters, including the size and number of hooks in the proboscis and the number of spines in the dorsal and ventral regions of the body. We inferred the phylogenetic relationships of 10 nominal species of Corynosoma through analysis of internal transcribed spacers (ITS-1, ITS-2) and 5.8S ribosomal RNA sequences. Nucleotide distances between species of Corynosoma ranged from 0.4 to 11% for ITS sequences. Maximum parsimony and likelihood analyses indicated that species of Corynosoma that inhabit hosts in the marine environment form a monophyletic assemblage, but yielded conflicting hypotheses for the relationship of Corynosoma cetaceum to other members of the genus. However, parsimony and likelihood analyses were consistent for many Corynosoma sister species relationships of (e.g., C. australe plus C. bullosum, C. validum plus C. villosum, C. caspicum plus C. magdaleni, and C. enhydri plus C. strumosum). This phylogenetic framework was used to evaluate taxonomic controversies concerning C. cetaceum and C. caspicum.