Description and phylogenetic position of an unusual genus and species of allocreadiid trematode from a characid freshwater fish in South America

The worldwide distributed family Allocreadiidae Looss, 1902 is predominantly parasitic in freshwater fish and occasionally in amphibians and reptiles. It contains 15 genera, of which only Allocreadium, Creptotrema, Wallinia and Creptotrematina have been reported in Argentina. The records of Allocreadium species still require further verification. The discovery of an allocreadiid digenean parasitizing Pseudocorynopoma doriae led us to erect a new genus for which the name Martorellia n. gen is proposed. It is characterized by poorly developed ventrolateral muscular lobes and a transversely elongated ovary, with the most characteristic feature being the presence of vitelline follicles in two fields (one anterior at level of ventral sucker and one posterior to the testis), which are not confluent in the middle. The phylogenetic tree reconstructed with 28S rDNA sequences placed the new genus as the sister taxa of Creptotrematina. Although both genera are separated by a small genetic distance, it is comparable with those separating other allocreadiid genera. The discovery of Martorellia liciae gen et sp. nov. provides further evidence of the great diversity of Allocreadiidae in South America. The analysis of new samples from different South American hosts with an integrative taxonomic approach as the one used here allows a better understanding of the evolutionary history and biogeography of allocreadiids in the Americas.