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In South America, the knowledge of trematode diversity parasitizing freshwater fishes is still scarce, as less than 5% of the freshwater fish fauna has been examined for parasites. A similar situation applies to studies on digenean life cycles, which have become increasingly rare. Among the digenean families parasitizing freshwater fishes in the region, Haploporidae is considered the richest in species diversity. However, information about the developmental stages of haploporid life cycles remains fragmentary. Particularly, in Argentina, nine cercariae attributed to the family Haploporidae have been described using morphological analysis, and only two life cycles of this family have been completely elucidated. In this study a new type of cercaria, morphologically assigned to the family Haploporidae and collected from the snail Heleobia parchappii (Cochliopidae) in Los Padres shallow lake, Buenos Aires province, was identified using morphological and molecular techniques. The molecular analysis, based on 28S and ITS2 sequences, revealed that the cercariae were 100% identical to adult specimens of Saccocoelioides nanii (Haploporidae) parasitizing the fish Prochilodus lineatus (Prochilodontidae) from Los Talas, Buenos Aires province. Our results not only provide information about the life cycle of S. nanii but also show that a molecular and morphological approach can be extremely useful in identifying the developmental stages of digeneans and elucidating their life cycles. [ABSTRACT FROM AUTHOR]

In the last years, a growing number of studies have focused on the search for biological indicators of human impact in freshwater environments. Given their susceptibility to different types of impact, larval digeneans have been considered as useful tools for the study of temporal variations in parasite communities. However, few studies have been carried out in lotic environments. For that reason, the spatio-temporal variations of the larval digenean assemblages parasitizing the gastropod Heleobia parchappii were analysed in four human-impacted streams, located on the coast of Argentina. In total, 4800 specimens of H. parchappii were collected seasonally, and 12 digenean species belonging to eight families were registered. Three of the streams showed similar species presence but, during spring and summer, the streams located within the city presented lower species presence than the streams located in the urban periphery. By contrast, the spatial prevalence values evidenced a higher variation between the environments. Streams located in the urban periphery showed higher prevalence values throughout the year, compared to those calculated for streams located within the city. The spatio-temporal variations of larval digenean assemblages parasitizing H. parchappii seem to be mainly influenced by the diversity and vagility of definitive hosts, the types of digenean life cycles and habitat characteristics. However, environmental disturbances derived from anthropogenic activities are highlighted as the probable main factors that may affect the composition and dynamic of these parasite assemblages. [ABSTRACT FROM AUTHOR]