In the Laboratory of Parasites of Fishes, Crustaceans and Mollusks (CEPAVE), we undertook a parasitological study on three species of fish from the Espinal and Esteros del Iberá ecoregions of Argentina. Clinostomid metacercariae were found parasitizing Characidium rachovii, Crenicichla vittata and Gymnogeophagus balzanii. In this study, we analysed the damage that these parasites inflict on their hosts through the evaluation of histological sections. In addition, Clinostomum metacercariae were identified using morphological characters and DNA barcoding. In the pathological analysis, we observed that muscle tissue was the most affected. The inflammatory response showed vascular congestion areas and infiltration of numerous inflammatory cells, mainly lymphocytes. The molecular and morphological approach supports the presence of three new lineages of clinostomid metacercariae in Argentina. This could lead to the discovery of a high number of lineages or species of Clinostomum from South America.

Two species of intestinal Capillariidae were hitherto known from the Neotropic cormorant Phalacrocorax brasilianus, Baruscapillaria spiculata (Freitas, 1933), and Baruscapillaria appendiculata (Freitas, 1933). The original descriptions are very short and brief, and further reports of both species are scarce and/or confusing. This paper provides a morphological redescription and molecular characterization, based on the partial 18S rDNA gene, of B. spiculata specimens parasitizing the Neotropic cormorant in two continental lagoons from Buenos Aires province, Argentina. Both morphological and morphometrical differences between B. spiculata and B. appendiculata are highlighted on the examination of available type material. Additionally, two previous reports of B. appendiculata from Mexico and Brazil are discussed. A phylogenetic analysis conducted on specimens of B. spiculata and 46 other capillariid isolates available from the GenBank demonstrated a sister-taxon relationship between our specimens and the type species of Baruscapillaria. But, at the same time, significant genetic distances between both taxa showed an interesting variability of the genus Baruscapillaria. The probable division of this genus into multiple genera could probably be confirmed through integrative studies including more species.

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The genus Clinostomum has been recently a subject of a large number of molecular phylogenetic studies that have uncovered a larger species diversity than we thought. In Argentina, only two nominal species have been reported, namely C. detruncatum and C. marginatum. Three putative species represented by metacercariae were recently molecularly diagnosed, and there are at least two additional metacercarial morphotypes diagnosed on morphological grounds. Here, we molecularly characterized specimens of Clinostomum sampled from freshwater fishes and fish-eating birds from Argentina through mtDNA cytochrome c oxidase subunit I (COI). Unexpectedly, the phylogenetic analysis uncovered three new additional genetic lineages, two of them corresponding to metacercarial stages and another matching COI sequences of C. heluans Braun, 1899, being considered conspecific, whereas the others still require formal description. Additionally, we add a new host species for a lineage molecularly diagnosed in a previous study. The adult specimens recovered from A. cocoi in Buenos Aires Province represented a new species clearly distinguished from the two species previously reported in Argentina. Clinostomum detruncatum is distinguished from the new species by possessing a characteristic tenoidean uterus, and testes located more posteriorly. Clinostomum marginatum is morphologically similar but differs from the new species in having rounded ovary, posterior testis lobated, and lateral cirrus-sac and displacing the anterior testis, and vitelline follicles not extending beyond the caeca end. Our study raises the number of Clinostomum species in Argentina up to 10. We describe the new species herein.