Description of Saccocoelioides miguelmontesi n. sp. (Digenea: Haploporidae) from characid fishes in the Iguazu River Basin based on morphological and molecular evidence.

Here we describe a new species of the genus Saccocoelioides found parasitizing Astyanax dissimilis Garavello & Sampaio, Psalidodon bifasciatus (Garavello and Sampaio) and Bryconamericus ikaa Casciotta, Almirón & Azpelicueta from the Iguazu National Park, Misiones province, Argentina. Saccocoelioides miguelmontesi n. sp. was studied based on morphological and molecular (28S rDNA and COI mtDNA sequences) data. The COI mtDNA tree indicated that the specimens collected from the three fish hosts are conspecific, with an intragroup p-distance of 0%. The new species shows an intermediate morphological configuration between the diminutive and robust forms described for Saccocoelioides by Curran (2018). Although, in the 28S rDNA tree, it is placed in a well-supported clade with the two robust species analysed (S. elongatus and S. magnus; p-distance of 1 and 2%, respectively), it differs from the robust group by the range of body size, mature egg size, oral and ventral sucker size, sucker ratio, oral sucker to pharynx ratio, and post-cecal or post-testis/body length percentage. Our results led us to redefine the robust group as having eggs shorter or equal in length to the pharynx. Saccocoelioides miguelmontesi n. sp. the 10th species reported from Argentina and the 7th species within the robust group.

Phylogenetic position of the Neotropical Family Zonocotylidae (Paramphistomoidea) using partial 28S rDNA sequences.

Six families belonging to the Paramphistomoidea superfamily have been reported in South America, with only Zonocotylidae and Balanorchiidae being endemic. The Zonocotylidae was initially classified as Aspidogastrea and then as a paramphistomoid. This family comprises a single genus, Zononocotyle, with two species. It is primarily characterized by having an attachment organ with transverse ridges and a single testis. The placement of Zonocotylidae within Paramphistomoidea is controversial, as some researchers speculate that this genus is the most primitive member of the superfamily, while others consider it an aberrant form. The main objectives of our study were to provide the first sequences of Zonocotylidae and elucidate its phylogenetic position. We amplified the 28S gene from two parasites from Cyphocharax sp. from Punta Lara, Buenos Aires. Newly generated sequences were used to infer the phylogenetic relationships with other Paramphistomoidea species using a Bayesian approach. Zonocotylidae were clustered with Dadayiinae and Kalitrematinae (Cladorchiidae) species found in freshwater fishes from South America. Genetic analyses revealed that they formed a well-supported clade with cladorchiids in freshwater hosts from South America. However, the occurrence of genera of Cladorchiidae in North America, Middle America, Asia, and Australia suggested its polyphyletic nature and may indicate the need for the erection of new families. Other Paramphistomoidea families may also require further revision. The addition of new sequences to phylogenetic analyses along with a comprehensive and more detailed description of the genera will help resolve the relationships within this group.

Integrative analysis of new Clinostomum metacercariae (Digenea, Clinostomidae) using COI mtDNA and morphology rises the number of lineages found in South American freshwater fishes.

Clinostomidae is a diverse family of digenean parasitizing fish-eating birds as adults and fishes as metacercariae. The species composition, within the genus Clinostomum has been steadily increasing in recent years. In Argentina, four named species of Clinostomum have been documented, accompanied by four metacercariae representing distinct genetic lineages whose adults have not been identified. This study focused on examining clinostomids in three fish species - Australoheros scitulus (ASI), Cichlasoma dimerus (CDIM), and Pimelodella laticeps (PLA) - at various localities in Argentina. We conducted both morphological and molecular characterizations of the Clinostomum metacercariae collected from these fish species. Molecular phylogenetic analyses using COI mtDNA were performed to determine the placement of these metacercariae within the clinostomid phylogenetic tree. Clinostomum ASC represents a distinct lineage, morphologically distinguishable from other sequenced metacercariae due to its body shape (widest anteriorly and becoming slender towards the posterior end); this lineage was found to be closely related to C. caffarae. While Clinostomum CDIM and Clinostomum PLA exhibited morphological differences, they clustered together genetically with metacercariae reported in previous studies as Clinostomum L3 and Clinostomum CVI. This outcome, coupled with a low genetic distance (0 to 3%), suggests that they are conspecific with metacercariae found in fish across Mexico, Costa Rica, and Argentina. In light of the extensive diversity of fish species in Argentine freshwater ecosystems (over 500 species), and considering the relatively constrained extent of prior investigations, the anticipation of unearthing additional Clinostomum species or lineages is plausible.

Description of Diegoglossidium maradonai n. g. and n. sp. (Digenea: Alloglossidiidae) through an integrative taxonomy approach, with an amended diagnosis of the family.

This paper describes Diegloglossidium maradonai n. g., n. sp. a parasite of the intestine of Hoplosternum littorale (Hancock) from La Plata River basin. The new genus is morphologically similar to members of Alloglossidiidae and Macroderoidiidae although they also share some traits observed in both families. Those families can be differentiated from each other by the combination of morphological features, including the density and distribution of the tegumental spines, the distribution of the vitelline follicles and the extent of the post-testicular space. The molecular analyses based on the large subunit of the ribosomal RNA gene, and the internal transcribed spacer (ITS) regions including ITS1, 5.8S and ITS2 unequivocally place the new genus in the family Alloglossidiidae which is amended based on new observed features. Diegoglossidium n. g. is characterized by a combination of characteristics, being most notably the presence of a deeply lobed ovary. Lastly, the geographical distribution and host associations of the two closely related Neotropical genera of Alloglossidiidae: Magnivitellinum and Diegoglossidium are discussed, and the host and distribution range of Magnivitellinum saltaensis is expanded into Argentina.

Metacercariae in the brain of Erythrinus cf. erythrinus (Characiformes: Erythrinidae) from Iguazú National Park (Argentina): do they belong to Dolichorchis lacombeensis (Digenea, Diplostomidae)?

In Argentina, the family Diplostomidae is composed of eight genera: Austrodiplostomum Szidat & Nani; Diplostomum von Nordmann; Dolichorchis Dubois; Hysteromorpha Lutz; Neodiplostomum Railliet; Posthodiplostomum Dubois; Sphincterodiplostomum Dubois; and Tylodelphys Diesing. During a parasitological survey of fishes from the Iguazú National Park we detected diplostomid metacercariae in the brain of Erythrinus cf. erythrinus. Fish were caught using crab traps, transported alive to the field laboratory, cold-anaesthetized and euthanized by cervical dissection. Some metacercariae were heat-killed in water and fixed in 10% formalin and others were preserved in alcohol 96% for DNA extraction. They were sequenced for the partial segment of the 28S rDNA, internal transcribed spacer (ITS) rDNA and cytochrome c oxidase subunit I (COI) mtDNA genes. Phylogenetic reconstruction was carried out using Bayesian inference and the proportion (p) of absolute nucleotide sites (p-distance) was obtained. In the 28S rDNA tree, the metacercaria sequenced grouped as Dolichorchis sp. The COI mtDNA p-distance between the metacercariae with Dolichorchis lacombeensis was 0.01. There is a small number of ITS sequences for the Diplostomidae family deposited in the GenBank. The oral sucker, ventral sucker, holdfast organ and the distance between oral and ventral suckers are larger in the adult compared with the metacercariae. Additionally, hind-body length and width are larger in the adult due to the development of the genital complex. Further studies using an integrative approach will help confirm the affiliation of other species to the genus Dolichorchis.