Mariana Bertholdi Ebert

The present study aims to describe a new genus and species of a plagiorchid digenean as a parasite of the callichthyid freshwater fish Osteogaster aenea from São Paulo State, Brazil. Detailed morphological analyses using light and scanning electron microscopy, combined with molecular characterization based on partial sequences of the 28S rDNA and COI mtDNA genes, were used to characterize the new species and to describe its phylogenetic position within the Digenea. Atriumlateralis capivarensis n. gen. et n. sp. is characterized by an elongate foliaceous body with smooth tegument, a ventral sucker larger than the oral sucker, obliquely arranged testes, dextral ovary, vitelline follicles arranged in two lateral clustered fields extending intra and extracaecally, and a laterally opening genital pore positioned immediately anterior to the ventral sucker. Phylogenetic analyses consistently recovered the new taxon as a well-supported monophyletic lineage, closely related to Choledocystus hepaticus. This study represents the first record of a mature digenean infecting O. aenea and contributes novel morphological and molecular data to the understanding of plagiorchiid diversity and systematics in Neotropical freshwater fishes.

Purpose The members of the genus Diaphorocleidus (Monopisthocotyla: Dactylogyridae) infest the gills, nostrils, and body surface of characiform freshwater fishes from the Neotropical region. We characterize a new species of Diaphorocleidus from the gills of three acestrorhamphid species from the Pardo River (a sub-basin of the Paranapanema River basin) in the state of São Paulo, Brazil. Methods This study includes phylogenetic analyses of molecular data (partial 28 S rDNA), as well as morphological and morphometric assessments of parasites collected from the gills of 140 fishes (i.e., 50 A. lacustris, 80 P. bockmanni, and 10 P. fasciatus). Results These analyses indicate that Diaphorocleidus pindamirim n. sp. is closely related to D. neotropicalis but differs primarily in the morphology of the copulatory complex and molecular data. The small subunit of the accessory piece is shaped like a chela (or fishing hook tip), which is not observed in D. neotropicalis, where the small subunit is claw-shaped. Conclusion Integrating morphological and molecular evidence, we describe a new species of Diaphorocleidus and propose a general morphometric scheme for the genus. These findings underscore that combining morphology with molecular data is essential for robust species delimitation and will advance taxonomic and parasitological research in the Neotropical region.

The genus Rondonia Travassos, 1920 comprises nematodes parasitizing teleost fishes and amphibians, but its taxonomic boundaries have long been uncertain due to limited morphological descriptions and lack of molecular data. Here, we provide an integrative taxonomic revision of Rondonia, combining light and scanning electron microscopy with molecular analyses of SSU and LSU rDNA sequences. A new species, Rondonia pardensis n. sp., is described from the intestine of Metynnis lippincottianus (Cope) (Characiformes: Serrasalmidae) in the Pardo River, Paranapanema River basin, Brazil. The new species is distinguished by the presence of a pre-bulbar excretory pore with a protruding teardrop-shaped structure covering it, the number and organization of the cloacal papillae (two pairs pre-cloacal, two pairs ad-cloacal and six pairs post-cloacal), the mouth with three bilobed lips bearing double papillae on each side arranged radially and two amphids, and a larger body size in comparison to its congeners. Phylogenetic analyses confirm its placement within Atractidae and support the monophyly of Rondonia. Based on morphological and molecular evidence, we propose a new taxonomic combination for specimens analysed by Cavalcante et al. (2016), herein reassigned as Rondonia xapuriensis nom. nov. We also examined the type material of Rondonia rondoni deposited by Travassos (1920) using SEM, confirming diagnostic features and recording additional characters that contribute to an updated morphological characterization of the species. In light of these findings, we propose an amended generic diagnosis for Rondonia that reflects its phylogenetic coherence and morphological consistency, and also a key for the identification of the Rondonia species. This study expands the known diversity of the genus, clarifies historical taxonomic uncertainties, and emphasizes the importance of integrative approaches for resolving the systematics of Atractidae.

The integration of molecular data with morphological analysis has greatly advanced the understanding of parasitic diversity, particularly within groups like Dactylogyridae. While morphological features have long been used to classify genera and species, molecular studies have often revealed discrepancies that challenge traditional taxonomies. Urocleidoides (Mizelle & Price, 1964) is one such example, with previous research suggesting it may not be monophyletic. Meanwhile, Annulotrematoides (Kritsky & Boeger, 1995) has lacked any molecular data until now, limiting our understanding of its evolutionary relationships. In this study, we provide the first molecular sequences for Annulotrematoides, which were grouped with Urocleidoides spp. Our analysis of Annulotrematoides bonaerensis Rossin & Timi, 2016 and Urocleidoides surianoae Rossin & Timi, 2016 found parasitizing the gills of Cyphocharax modestus (Fernández–Yépez) revealed a strong phylogenetic relationship between these two species, despite their classification in different genera. This discovery challenges the current morphological–based taxonomy of Urocleidoides and suggests that U. surianoae may not be accurately placed within its genus. The clustering of Urocleidoides with Annulotrematoides for the first time highlights the need for a taxonomic re–evaluation of these groups. Additionally, this work underscores the importance of molecular data in resolving evolutionary relationships and advancing our understanding of parasitic diversity.

Tereancistrum is a common genus of Neotropical monopisthocotylans; however, information on its diversity and phylogeny remains limited. In this study, we describe four new species of Tereancistrum parasitizing the gills of Prochilodus brevis (Characiformes: Prochilodontidae) from a weir in the state of Ceará, Brazil. Tereancistrum spiralocirrum n. sp. and Tereancistrum scleritelongatum n. sp. are characterized by a dextro-ventral vaginal pore and a Y-shaped dorsal bar. Notably, Tereancistrum spiralocirrum n. sp. is the first species in the genus to possess a male copulatory organ (MCO) with multiple rings (16 to 18). In contrast, Tereancistrum ancistrum n. sp. and Tereancistrum kritskyi n. sp. are distinguished by a sinistral vaginal pore, a sclerotized MCO in the form of a coiled tube with slightly more than one clockwise ring, and an accessory piece that is non-articulated with the base of the MCO. However, Tereancistrum ancistrum n. sp. is unique in lacking a dorsal bar. Sequences of the LSU rDNA obtained from seven species of Tereancistrum parasitizing P. brevis and Leporinus piau, along with published sequences of other Dactylogyridae members, were included in the molecular analyses. Phylogenetic reconstructions supported the monophyly of Tereancistrum.

While most higher taxa in the Hemiuroidea exhibit remarkable diversity and thrive worldwide in marine ecosystems, a few groups have successfully radiated into freshwater environments. Among them, species of Thometrema are well known from freshwater and brackish fishes in the New World. In this study, specimens of Thometrema from a single specimen of the endangered pimelodid catfish Steindachneridion scriptum in the Upper Paraná River basin, State of São Paulo, Brazil, were subjected to morphological, ultrastructural (first scanning electron microscopy data for the genus) and molecular analyses. Newly obtained sequences of the partial large subunit nuclear ribosomal RNA (28S rDNA) and partial mitochondrial cytochrome c oxidase subunit I (COI mtDNA) provided strong evidence supporting the identification of the specimens as T. patagonicum, a trematode previously known only from endemic percichthyid fishes (Percichthyidae) in the Argentinian Patagonia. This unexpected finding, along with critical morphological evaluation of new and deposited material, led us to propose T. overstreeti and T. bonariense as junior synonyms of T. patagonicum. Moreover, we reassessed certain morphological features, revealed new potential distinguishing characters (papillae) and raised doubts about the taxonomic value of commonly used features for species differentiation (e.g., vitellarium masses). To overcome taxonomic problems in Thometrema due to the paucity of morphological features to clearly set species boundaries, new descriptions could leverage integrative approaches, as employed here, to establish robust species hypotheses and ultimately unravel the actual species composition in the Americas.

The present study describes two new species of monopisthocotylans parasitizing the gills of Cyphocharax modestus (Characiformes: Curimatidae) from two localities of the Upper Paraná River basin, state of São Paulo, Brazil. Urocleidoides saghirus n. sp. and Urocleidoides taquariensis n. sp. differ from other congeners mainly in the morphology of the accessory piece: comprising two subunits (one scythe-shaped subunit, and one adjacent piece with a narrow base broadening towards the upper end, which is axe-shaped) in Urocleidoides saghirus n. sp., and a straight rod with a bifurcated proximal portion, a distal portion ending in a point, and two curved handles arising from the medial portion and uniting close to the distal portion in Urocleidoides taquariensis n. sp. The phylogenetic analyses revealed Urocleidoides to be non-monophyletic, indicating the need for a taxonomic review. This study provides the first molecular sequences for Urocleidoides spp. parasitizing Curimatidae, including the newly described species. These findings revealed distinct clades and suggested possible host specificity, underscoring the importance of additional research to better understand the phylogenetic relationships within the genus.

We described Creptotrema cambeve n. sp. from the intestine of the Brazilian catfish Cambeva davisi (Haseman, 1911) (= Trichomycterus davisi) based on integrative analyses using morphological and molecular approaches. Creptotrema cambeve n. sp. closely resembles morphologically Creptotrema paraense Vicente, Santos & Souza, 1978, which was described from a siluriform fish in Northern Brazil; however, the two species differ mainly in the oral and ventral sucker sizes and the distribution of the vitellaria. The phylogenetic analyses of the 28S rDNA placed the sequences of the new species in a monophyletic clade together with all other Creptotrema spp. and as sister taxon of Creptotrema cruste Alcantara, Ebert, Ferreira-Silva, Forti, Morais, Pérez-Ponce de León & Silva, 2024, a parasite from a Brazilian anuran. Genetic divergences between the new species and other Creptotrema spp. varied from 0.2% to 4.3%, further corroborating the distinction of the new taxon. Creptotrema cambeve n. sp. is the 18th nominal Creptotrema species known from South America and the 22nd erected in the genus. This is the first study reporting a trematode in Cambeva spp. hosts and the second parasitological survey carried out for Ca. davisi, a poorly known small endemic fish.

Background Allocreadiids are relatively small digeneans that appear to be restricted to freshwater systems distributed across the world. Allocreadiids are highly diverse in the Americas, particularly in the Neotropical biogeographical region. Their taxonomic history has been rather controversial, with several taxonomic reassessments and the description of new genera and species. Methods We sampled Creptotrematina specimens from a characid collected in the Pardo River, Paranapanema River basin in Brazil, and specimens of C. aguirrepequenoi, from Astyanax spp. in several localities between northern Mexico and Costa Rica. The specimens were studied through integrative approaches using morphological and molecular analyses of the 28S rDNA gene and two different regions of the COI mtDNA gene. Results We describe a new species of Creptotrematina which is differentiated from other congeners by the overall body size, but in particular by the size and position of the cirrus-sac, distribution of the vitelline follicles, and extension of uterine loops in the posterior end of body. Phylogenetic analyses of the 28S rDNA and COI mtDNA genes placed the new species in a monophyletic clade together with all other sequenced species of Creptotrematina, and as a sister species of C. batalhensis. Genetic divergences between the new species and other Creptotrematina spp. varied from 1.1 to 1.2% for the 28S rDNA and 12.4–14.3% for the COI mtDNA. Phylogenetic analysis based on COI mtDNA showed the isolates of C. aguirrepequenoi grouped in four monophyletic clades representing populations geographically separated along a wide geographical range spanning between northern Mexico and Costa Rica, with an estimated genetic divergence between 3.9% and 8.9%. Conclusions Our findings based on integrative analyses recognize Creptotrematina saltograndensis n. sp. from a characid collected in the Pardo River, Paranapanema River basin in Brazil and provide validation of the wide geographical distribution of C. aguirrepequenoi across Middle-America parasitizing Astyanax spp.; the genetic divergence of the species through the analysis of two regions of COI mtDNA points towards considering it represent a species complex, although we refrain at the moment on describing a new species, awaiting for further verification using other molecular markers, and obtaining fresh material for a more detailed taxonomic analyses. This study increases the known diversity of allocreadiids and contributes to the understanding of evolutionary relationships, host-parasite relationships, and biogeographic history of the group.