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The dactylogyrid genus Rhinoxenus (Monogenea: Dactylogyridae) is composed of specialized monogeneans infecting the nasal cavities of freshwater fishes from the Neotropical region. This taxon currently comprises 11 species and is easily distinguished from other monogeneans by the absence of the dorsal bar, ventral anchor with inconspicuous roots covered by a sclerotized cap, dorsal anchor greatly modified into a needle-like shape, and hook pair 2 located into bilateral lobes of the trunk. Specimens of Rhinoxenus euryxenus and Rhinoxenus paranaensis were found infecting the nasal cavities of Serrasalmus marginatus and Serrasalmus maculatus, respectively, from the Paraná River basin in Brazil. For the first time, molecular data of Rhinoxenus spp. were obtained and used as a basis for phylogenetic analyses of the genus. Furthermore, our findings represent the first record of R. paranaensis in Brazil.

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Oncoceratium n. gen. is proposed to accommodate Oncoceratium amphidactylum n. gen. n. sp. (Monogenoidea, Gyrodactylidae). Although the proposed genus is monotypic, the differences presented in the diagnosis clearly establish it as distinct from species from other genera, such as Gyrodactylus von Nordmann, 1832 and especially those that occur exclusively in the Neotropical region. The new genus is diagnosed by the presence of a bulbous male copulatory organ, with one row of spinelets of similar sizes and shapes, while the only spine usually found in the gyrodactylids is absent or not differentiated; a haptor with anchors presenting points folded outwards, and superficial and deep roots continuous and indistinguishable; the absence of a deep bar; and hooks in two bilateral clusters of eight hooks. Oncoceratium amphidactylum n. gen. n. sp. is described from the tamboatá fish, Hoplosternum littorale (Hancock) (Callichthyidae), and is characterized by the presence of a pair of horn-shaped anchors with the point turned outwards, a superficial bar shield and absent deep bar, hooks disposed in bilateral lobes, and a MCO with no spine or with a row with large spinelets visible in place of the spine. In addition to the morphological features, distance analysis and Bayesian inference, based on 5.8s and partial ITS2, support placing the new species in a new genus, and not including it in a cluster of species of Gyrodactylus and near to Gyrodactyloides bychowskii Albova, 1948, Ieredactylus rivuli Schelkle et al., 2011 and Laminiscus gussevi (Bychowsky & Polyansky, 1953) Pálsson & Beverely-Burton, 1983.

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Henneguya polarislonga n. sp. is described from the gills of Astyanax lacustris (Lütken, 1875) (Characiformes, Characidae) from streams of the Middle Paranapanema River, Upper Paraná River basin, in the São Paulo State, Brazil. The proposed new species is supported by a combination of morphological and molecular characterization (partial fragment of the SSU rDNA). Thirty specimens of A. lacustris were analyzed and myxospores were found in the gill lamellae of one specimen (Prevalence = 3.3%). Henneguya polarislonga n. sp. was morphometrically and genetically distinct from other Henneguya spp. previously described in Astyanax spp., mainly differing in the total length and caudal appendages length of the mature myxospores. Comparative analysis of the SSU rDNA sequences revealed that Seisactinomyxon-type actinospores previously reported parasitizing oligochaetes are developmental stages of the life cycle of Henneguya polarislonga n. sp. (similarity of 99.9%). This is the first time that an actinospore and a myxospore are correlated through molecular analysis in Brazil, contributing to the knowledge of the myxozoan ecology and biodiversity.

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A new parasitic copepod, Tiddergasilus bipartitus n. sp. (Copepoda, Ergasilidae), is described herein based on three adult females found attached to the gills of the yellow-tail lambari Astyanax lacustris (Lütken), sampled in Pardo River, municipality of Botucatu, São Paulo State, Brazil. Tiddergasilus bipartitus n. sp. was recognized as a new member of the monotypic genus Tiddergasilus Marques & Boeger, 2018 by having: antennule 6-segmented; maxillary basis armed with 2 terminal teeth and ornamented with multiple spinules; second and third leg both with endopod 3-segmented. The new copepod can be distinguished from its congener, Tiddergasilus iheringi (Tidd, 1942), by the morphology of the antennal claw, number of somites/segments in abdomen and fourth leg, and by the ornamentation of the first leg. This report expands the geographic distribution and diversity of fish species parasitized with Tiddergasilus spp. in Brazil. Moreover, it also represents the first report of an ergasilid species in the Pardo River. A list of diagnostic features for the Brazilian species of Ergasilus von Nordmann, 1832 is provided herein, in order to aid comparisons with the species of this complex genus.

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PURPOSE: We describe two new species of Myxobolus (Myxobolidae) found parasitizing Mugil curema from two locations in Brazil: Myxobolus curemae n. sp. from gill arch and rays and Myxobolus maceioensis n. sp. from gill lamellae. METHODS: We based the descriptions on myxospore morphology, histology, and small-subunit ribosomal DNA sequences. RESULTS: Myxospores of the two new species had similar morphology and morphometry but differed in spore body width and length, and ssrDNA sequences differed by 10.5%. These data supported the diagnosis of the parasites as distinct and novel species. The phylogenetic analysis showed a subclade formed by species that parasitize Mugiliformes, with M. maceioensis n. sp. as a sister species of Myxobolus episquamalis and Myxobolus bizerti, while there is a group of six species that are sister related to M. curemae n. sp. Our analysis was consistent with previous studies suggesting that orders of the hosts are strongly correlated with phylogenetic signals in the Myxobolidae. CONCLUSIONS: Myxobolus curemae n. sp. and M. maceioensis n. sp. are new species identified parasitizing M. curema.

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About forty-two species of Myxobolus have been previously described to parasitize characiform fishes in South America. Here, we described a new myxozoan species, Myxobolus parodontidis n. sp., in the gills of Apareiodon piracicabae (Characiformes, Parodontidae) from the streams of the Middle Paranapanema River basin, Brazil. The proposed new species is supported by a combination of morphological, ultrastructural, and molecular characterization (small subunit ribosomal DNA). Thirteen specimens of A. piracicabae were analyzed and 30.8% was infected by Myxobolus parodontidis n. sp. The myxospores was classified as intralamellar asymmetric type. A few aberrant myxospores with three polar capsules were observed: the spore length and width were the same of normal myxospores, but the polar capsules had smaller sizes. Ultrastructural analysis showed that the plasmodial membrane of Myxobolus parodontidis n. sp. was in direct contact with the host tissue and a connective capsule surrounding the plasmodium was not observed. The phylogenetic analysis showed that the main influence in the clustering of species of myxobolids seems to be related to the phylogenetic relationships established among fish hosts, mainly at the level of family and order. This is the first record of a myxozoan species parasitizing parodontid fish, contributing to the knowledge of the biodiversity of myxozoans from Brazil.

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We describe Myxobolus cataractae n. sp., found parasitizing Imparfinis mirini from Cachoeirinha stream, a tributary of Pardo River, Paraná River basin, municipality of Botucatu, São Paulo State, Brazil. We based the description on myxospore morphology, histology, and small subunit ribosomal DNA partial sequences. Whitish and elongated mass of myxospores were found in gill filaments, occupying an intrafilamental position. The myxospores were slightly ellipsoidal and the morphometric measurements revealed a myxospore body length of 7.8 ± 0.4 µm; myxospore width of 5.9 ± 0.4 µm; and thickness of 3.9 ± 0.3 µm. The polar capsules are equal in size and measured 3.5 ± 0.2 µm in length and 1.7 ± 0.2 µm in width. The polar tubules had 6-7 coils. Myxobolus cataractae n. sp. is classified as the intrafilamental type and chondreal subtype by the histological analysis of gills. Phylogenetic analysis showed a well-supported subclade formed by species that parasitize gills of Siluriformes, with M. imparfinis as a sister species of Myxobolus cataractae n. sp. Using molecular and morphological characterization, this cryptic species was identified as a new species of the genus Myxobolus.

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PURPOSE: We describe two new Henneguya spp. (Myxobolidae) found parasitizing Cyphocharax modestus from Pardo river, Paraná river basin, municipality of Botucatu, São Paulo State, Brazil: Henneguya fastigata n. sp. from gill lamellae and Henneguya pardensis n. sp. from gill arches. We based the descriptions on myxospore morphology, histology, and small subunit ribosomal DNA sequences. METHODS: In this investigation, 50 specimens of Cyphocharax modestus were examined between July and December 2020 for myxozoan infections. Morphological characterization was based on the mature myxospores. The small subunit ribosomal DNA sequences were used for molecular and phylogenetic study. RESULTS: Phylogenetic analysis provided the evolutionary position of these new species with other myxobolids species. Myxospores of the two species had similar morphology and morphometrics, but differed in spore body width and length, and ssrDNA sequences differed by 7.2%. These data supported the diagnosis of the parasites as distinct and novel species. The phylogenetic analysis showed a well-supported subclade formed by species that parasitize curimatid fishes, with Henneguya gilbert as a sister species of Henneguya fastigata n. sp., and Henneguya pardensis n. sp. as a sister species of both species. CONCLUSION: Our analysis was consistent with previous studies suggesting that orders and families of the hosts are strongly correlated with phylogenetic signals in the Myxobolidae. These are the first species of myxozoans described in the Pardo river.

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Abstract: A new species of Phanerothecium Kritsky & Thatcher, 1977 (Oogyrodactylidae Harris, 1983) is described from locariid fish from southeast Brazil. Phanerothecium macrosomum n. sp. (Oogyrodactylidae) is described from the body surface of Hypostomus regani (Ihering, 1905) (Loricariidae). It is characterized by an armed male copulatory organ containing spines of different size from proximal to distal extremity, short peduncle and robust haptor.

Resumo: Uma nova espécie de Phanerothecium Kritsky & Thatcher, 1977 (Oogyrodactylidae Harris, 1983) é descrita em peixes locariídeos do sudeste do Brasil. Phanerothecium macrosomum sp. n. (Oogyrodactylidae) é descrito da superfície corporal de Hypostomus regani (Ihering, 1905) (Loricariidae) e é caracterizado pela presença de órgão copulador masculino armado contendo espinhos de diferentes tamanhos da extremidade proximal à distal, pedúnculo curto e haptor robusto.

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Myxozoans are microscopic cnidarians that mainly parasitize fishes. The present study aimed to describe a new myxozoan parasite from the gills of Boulengerella cuvieri (Spix and Agassiz, 1829) by morphological and molecular analysis. The fish was collected in 2019 at the Pindaíba River, municipality of Cocalinho, Mato Grosso State, Brazil. Whitish and circular plasmodia were found in the primary gill filaments, occupying an intralamellar position, with an average of 0.5 mm in diameter. Henneguya Thélohan, 1892 myxospores found inside the plasmodia were elongated and ellipsoidal, consisting of two long and elliptical shell valves with two long, tapering caudal appendages. Morphometric measurements revealed a total spore length of 36.1 ± 2.0 µm; spore body length of 12.8 ± 0.5 µm; spore width of 4.9 ± 0.3 µm; tail length of 23.3 ± 1.6 µm; capsule length of 7.2 ± 0.4 µm; capsule width of 1.5 ± 0.2 µm; and 10 coils in the polar filament. Phylogenetic analysis showed that the isolates from this study were grouped into the main-clade of freshwater fishes, within a group of species parasitizing fishes from Brazil. Intergenotypic difference ranged from 23%-25.9% compared with other Brazilian myxozoan isolates. Using molecular and morphological characterization, this parasite was identified as a new species of the genus Henneguya.

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The present study describes Henneguya tietensis n. sp. parasitizing Prochilodus lineatus (Valenciennes, 1837) from Brazil, through morphological and molecular analysis. Myxospores were found in the gill tissue of P. lineatus with a prevalence of 10%. The myxospores consisted of two elongate, elliptical shell valves each with a long, tapering caudal appendage. The morphology was consistent with Henneguya and the myxospore measured as follows (mean ± SD): total length 55.5 ± 2.1 µm, body length 16.2 ± 1.1 µm, body width 5.5 ± 0.1 µm, caudal appendages length 39.0 ± 2.0 µm. The polar capsules were 7.3 ± 0.2 µm long, 1.7 ± 0.2 µm wide and contained a polar filament coiled 11 to 13 turns. Histological analysis showed the plasmodia developing in the middle region of each gill filament and caused a focally extensive distension by forming a space-occupying mass within the gill filament. The ultrastructural analysis allowed the observation of the presence of mature myxospores throughout the plasmodium. Phylogenetic analysis with the SSU rDNA gene showed Henneguya tietensis n. sp. as a sister species of the subclade formed by Henneguya piaractus and Henneguya brachypomus that infect fishes of the genus Piaractus. The genetically closest species was H. piaractus, which showed a similarity of 82.4%. Using molecular and morphological characterization, the myxozoan parasite described herein represents a new species of the genus Henneguya.

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Plasmodia containing myxospores belonging to the genus Henneguya Thélohan, 1892 were found in the gills of Eugerres brasilianus (Cuvier, 1830). Despite the economic importance, few parasitological studies have been done with this species. We describe Henneguya lagunensis n. sp. using morphological and molecular data. The mature myxospores were rounded, measuring 29.1 ± 2.2 µm in total length, 8.2 ± 1.0 µm in body length, 7.9 ± 0.2 µm in body width, 20.7 ± 2.4 µm in tail length and 4.8 ± 1.0 µm in thickness. The polar capsules measured 3.3 ± 0.4 in length and 1.7 ± 0.3 µm in width. Polar filaments had 4-5 turns, helical. Phylogenetic analysis showed Henneguya lagunensis n. sp. as a sister species of Henneguya cynoscioni Dyková, Buron, Roumillat and Fiala, 2011, within a clade that contained mostly Henneguya species that parasitize marine fish of the order Perciformes. This is the first report of a species of Henneguya parasitizing Eugerres brasilianus.

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A total of 53 tamboatás, Hoplosternum littorale, from the Batalha River, São Paulo, southeastern Brazil, were examined between February 2014 to December 2016. Seventeen species of parasites were identified, and 961 specimens were collected. The richness of each community varied from one to seven species of parasites per fish. The metacercariae of Diplostomum lunaschiae showed higher prevalence and mean abundance, being the core species. Gyrodactylus sp. obtained a higher mean intensity value. Aporocotylidae gen. sp. showed a significant negative correlation between its abundance and the standard host weight and length, while Spiroxys sp. showed a significant negative correlation between its abundance and the host weight. The high parasitic diversity of this host in Batalha River confirm it is an important site for maintaining local biodiversity with a relevant contribution to the knowledge of freshwater biodiversity in the State of São Paulo. Gyrodactylidae gen. sp., Austrodiplostomum mordax, Aporocotylidae gen. sp., D. lunaschiae, Diplostomidae gen. sp. 1, Contracaecum sp., Dioctophyme renale, Porrocaecum sp., Pseudocapillaria sp. 1, Pseudocapillariasp. 2, Spiroxys contortus, Oligobdella sp., and Lernaea cyprinacea are parasites mentioned for the first time in H. littorale. Aporocotylidae gen. sp., Gyrodactylidae gen. sp., and Oligobdella sp. are new species in process of taxonomic description by the authors of the present study.(AU)

Um total de 53 tamboatás, Hoplosternum littorale, coletados no rio Batalha, São Paulo, sudeste do Brasil, foram examinados entre fevereiro de 2014 a dezembro de 2016. Dezessete espécies de parasitos foram identificadas e 961 espécimes foram coletados, com riqueza parasitária de uma a sete espécies de parasitos por peixe. As metacercárias de Diplostomum lunaschiae apresentaram maior prevalência e abundância média, sendo a única espécie central. Gyrodactylus sp. obteve o maior valor de intensidade média. Aporocotylidae gen. sp. mostrou uma correlação negativa significativa entre sua abundância e o peso e comprimento padrão do hospedeiro, enquanto Spiroxyssp. apresentou correlação negativa significativa entre sua abundância e o peso do hospedeiro. A alta diversidade parasitária deste hospedeiro no rio Batalha confirma a importância desse local para a manutenção da biodiversidade da região, e o presente estudo traz contribuições relevantes para o conhecimento da biodiversidade de água doce no Estado de São Paulo. Gyrodactylidae gen. sp., Austrodiplostomum mordax, Aporocotylidae gen. sp., D. lunaschiae, Diplostomidae gen. sp. 1, Contracaecum sp., Dioctophyme renale, Porrocaecum sp., Pseudocapillaria sp. 1, Pseudocapillariasp. 2, Spiroxys contortus, Oligobdella sp., e Lernaea cyprinacea são parasitos mencionados pela primeira vez em H. littorale. Aporocotylidae gen. sp., Gyrodactylidae gen. sp., e Oligobdella sp. são novas espécies em processo de descrição taxonômica pelos autores do presente estudo.(AU)

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A total of 53 tamboatás, Hoplosternum littorale, from the Batalha River, São Paulo, southeastern Brazil, were examined between February 2014 to December 2016. Seventeen species of parasites were identified, and 961 specimens were collected. The richness of each community varied from one to seven species of parasites per fish. The metacercariae of Diplostomum lunaschiae showed higher prevalence and mean abundance, being the core species. Gyrodactylus sp. obtained a higher mean intensity value. Aporocotylidae gen. sp. showed a significant negative correlation between its abundance and the standard host weight and length, while Spiroxys sp. showed a significant negative correlation between its abundance and the host weight. The high parasitic diversity of this host in Batalha River confirm it is an important site for maintaining local biodiversity with a relevant contribution to the knowledge of freshwater biodiversity in the State of São Paulo. Gyrodactylidae gen. sp., Austrodiplostomum mordax, Aporocotylidae gen. sp., D. lunaschiae, Diplostomidae gen. sp. 1, Contracaecum sp., Dioctophyme renale, Porrocaecum sp., Pseudocapillaria sp. 1, Pseudocapillariasp. 2, Spiroxys contortus, Oligobdella sp., and Lernaea cyprinacea are parasites mentioned for the first time in H. littorale. Aporocotylidae gen. sp., Gyrodactylidae gen. sp., and Oligobdella sp. are new species in process of taxonomic description by the authors of the present study.

Um total de 53 tamboatás, Hoplosternum littorale, coletados no rio Batalha, São Paulo, sudeste do Brasil, foram examinados entre fevereiro de 2014 a dezembro de 2016. Dezessete espécies de parasitos foram identificadas e 961 espécimes foram coletados, com riqueza parasitária de uma a sete espécies de parasitos por peixe. As metacercárias de Diplostomum lunaschiae apresentaram maior prevalência e abundância média, sendo a única espécie central. Gyrodactylus sp. obteve o maior valor de intensidade média. Aporocotylidae gen. sp. mostrou uma correlação negativa significativa entre sua abundância e o peso e comprimento padrão do hospedeiro, enquanto Spiroxyssp. apresentou correlação negativa significativa entre sua abundância e o peso do hospedeiro. A alta diversidade parasitária deste hospedeiro no rio Batalha confirma a importância desse local para a manutenção da biodiversidade da região, e o presente estudo traz contribuições relevantes para o conhecimento da biodiversidade de água doce no Estado de São Paulo. Gyrodactylidae gen. sp., Austrodiplostomum mordax, Aporocotylidae gen. sp., D. lunaschiae, Diplostomidae gen. sp. 1, Contracaecum sp., Dioctophyme renale, Porrocaecum sp., Pseudocapillaria sp. 1, Pseudocapillariasp. 2, Spiroxys contortus, Oligobdella sp., e Lernaea cyprinacea são parasitos mencionados pela primeira vez em H. littorale. Aporocotylidae gen. sp., Gyrodactylidae gen. sp., e Oligobdella sp. são novas espécies em processo de descrição taxonômica pelos autores do presente estudo.

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The present study describes Henneguya lacustris n. sp. parasitizing Astyanax lacustris (Lütken 1875), from the Tietê River, State of São Paulo, Brazil, through morphological and molecular analysis. Myxospores of the parasites were found in the gills of A. lacustris with 13% prevalence of infection. The myxospores were oval and presented as measures (mean ± standard deviation): total length 18.3 ± 2.2 µm, body length 10.4 ± 1.6 µm, body width 4.9 ± 0.9 µm, tail length 7.2 ± 2.5 µm. The polar capsule was 4.8 ± 0.3 µm long and 1.5 ± 0.2 µm wide. The polar tubules, present inside the polar capsules, had 6 to 7 turns. The ultrastructural analysis allowed the observation of the asynchronous development of the myxospores. Phylogenetic analysis showed H. lacustris n. sp. as a sister species of H. chydadea Barassa and Cordeiro 2003 in a subclade formed by species that parasitize the gills of Characiform fish from Brazil. Using molecular and morphological characterization, this parasite was identified as a new species of the genus Henneguya Thélohan 1892.

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Among several marine pelagic species of the Brazilian coast, Scomber colias Gmelin, 1789 (Perciformes: Scombridae) stands out for having great economic importance, since it is widely used as a food resource and presents moderate vulnerability. Twenty specimens of S. colias were purchased from October 2015 to October 2016 from the coast of Santa Catarina, Brazil. In the present study, we recorded Hysterothylacium fabri (Rudolphi, 1819) (Deardorff and Overstreet, Proc Biol Soc Wash 93(4):1035-1079 1980) from the S. colias intestine using an integrative taxonomy approach, where morphological data are used in combination with partial sequences of the ITS gene, to validate the taxonomic status of the species and establish their relationships with other members of the genus. This species is being recorded for the first time in the South Atlantic and S. colias. The specimens of H. fabri collected in this study parasitizing S. colias presented morphology similar to the other specimens already registered parasitizing other hosts. The distance matrix generated showed that the partial sequences obtained in this study were more similar to sequences of Hysterothylacium sp. collected in China. In phylogenetic analysis, the two detected haplotypes of this study were grouped with H. fabri haplotypes deposited in GenBank in a monophyletic subclade.

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On the basis of morphological and molecular analyses, a new myxozoan parasite is described from the gills of the fish Hoplerythrinus unitaeniatus, collected in the municipality of Nova Xavantina, Mato Grosso State, Brazil. Plasmodia of Henneguya unitaeniata sp. nov. were oval and whitish and were found surrounded by collagen fibers forming plasmodia wall between gill filaments on the gill arch. The spores were ellipsoidal with two similar polar capsules. Morphometric analysis showed a total spore mean length of 23.8 ± 1.5 µm, spore body mean length of 14.5 ± 0.7 µm, caudal appendage mean length of 10.3 ± 1.4 µm, thickness mean length of 4.3 ± 0.3 µm, polar capsule mean length of 4.2 ± 0.5 µm, polar capsule mean width of 1.8 ± 0.3 µm, spore mean width of 4.8 ± 0.4 µm, and 4-5 polar filament coils. Phylogenetic analysis showed Henneguya unitaeniata sp. nov. as a basal species in a subclade formed by myxozoans that parasitize bryconid fishes.

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Plasmodia containing spores of a new species of myxozoan, Henneguya jundiai n. sp., were found in the gill arches of Rhamdia quelen catfish. The present study describes H. jundiai n. sp. based on morphological and molecular analysis. The mature spores were elongated and measured 26.9 ± 1.9 (22.9-29.2) µm in total spore length, 9.5 ± 0.4 (8.8-10.0) µm in spore body length, 4.6 ± 0.4 (4.1-5.5) µm in spore body width, 17.3 ± 1.8 (14.1-19.8) µm in tail length, 4.9 ± 0.3 (4.6-5.5) µm in polar capsule length and 1.4 ± 0.2 (1.2-1.7) µm in polar capsule width. The polar filaments had 6-7 coils. Histological analysis revealed the formation of a large plasmodium connected to the gill arch through the epithelial tissue. Ultrastructural analysis revealed the presence of a binucleated sporoplasm, as well as the polar capsules and the coils of the polar filament. Phylogenetic analysis found that H. jundiai n. sp. is located within a subclade formed by species of Henneguya which parasitize siluriform fish from Brazil. Henneguya jundiai n. sp. appears as a sister species of H. quelen. The results of the analyzes clearly indicated the existence of a new species, H. jundiai.

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The Diplostomidae include a large group of flatworms with complex life cycles and are frequently found parasitizing the eyes and central nervous system of freshwater fishes. The morphological identification of the metacercariae at species level is not always possible. Thus, molecular tools have become essential to assist in the parasite species determination. This study was aimed at describing two diplostomid metacercariae found in freshwater fish in São Paulo, Brazil, based on morphological characters and in the genetic characterization of COI sequences. Our results showed that the two recognized taxa (Tylodelphys sp. and Diplostomidae gen. sp.) appear to be different from the species already described in South America. Tylodelphys sp. differs morphologically from Tylodelphys xenopi, T. mashonense, T. jenynsiae, and T. scheuringi. The metacercariae of T. clavata and T. conifera are smaller than Tylodelphys sp., while T. podicipina is larger than the metacercariae described here. The phylogenetic analysis of COI sequences yielded Tylodelphys sp. as the sister species of Tylodelphys sp. 4, a species reported from the brain of the eleotrid Gobiomorus maculatus in Oaxaca, Mexico. The metacercariae identified as Diplostomidae gen. sp. are morphologically different from the known diplostomid metacercariae and did not match with other diplostomid sequences available. Diplostomidae gen. sp. is recovered as the sister species of Diplostomum ardeae. Although the morphological evidence and the COI sequences differentiate the metacercariae found, the absence of adult specimens of both species precludes the specific designation. This is one of the first papers that use an integrative taxonomy approach to describe the species diversity of diplostomid trematodes in Brazil.

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A mass of free myxozoan spores was found in the gill filaments of specimens of Cetopsorhamdia iheringi Schubart and Gomes, 1959, popularly known as "three-barbeled catfishes" (Heptapteridae, Siluriformes) collected in streams of the Middle Paranapanema River, Upper Paraná River basin, in the state of São Paulo, Brazil. Morphological and molecular analysis identified the spores as Myxobolus imparfinis Vieira, Tagliavini, Abdallah and Azevedo, 2018. The ultrastructural morphology of this parasite is described here for the first time. Differences were observed in the number of coils of the polar filament as well as some organelles not previously described for this species. Asynchronous development was also observed, with the presence of both mature and immature spores. This is the first report of a myxozoan parasitizing C. iheringi and the first geographical record of myxozoan parasites in streams of the Middle Paranapanema River. The new data improve the original description of the species and add to the knowledge of host-parasite interactions and distribution.

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