Where are the South American freshwater turtle blood flukes (Trematoda: Spirorchiidae)? The first morphological and molecular analysis of spirorchiid cercariae from freshwater snails in Brazil

•The occurrence of freshwater spirorchiids in South America is reported for the first time.•Morphological and molecular data are presented for South American species of Spirorchiidae for the first time.•The involvement of a caenogastropod snail as intermediate host of these parasites is presented.•The paraphyly of the members currently included in the family Spirorchiidae is reconfirmed.

Trematodes belonging to the family Spirorchiidae are blood parasites mainly of turtles with a worldwide distribution. These flukes were recently reported in some marine turtles from South America, where the occurrence of spirorchiids in freshwater definitive and intermediate hosts is so far unknown. In the present study, three morphotypes of brevifurcate apharyngeate distome cercariae found in freshwater molluscs from an urban reservoir in Brazil were used for morphological and molecular (nuclear 28S rDNA) evaluation. Two morphotypes of cercariae, probably congeneric species, were found in 12/17,465 specimens of Biomphalaria spp. and differ from each other by body size and sequences (0.1%). They present morphology similar to North American freshwater spirorchiids (Spirorchis spp.), however surprisingly molecular data reveals that these lineages are more closely related to marine spirorchiids. A third species found in 2/777 Pomacea sp. differs morphologically from all previously described spirorchiid cercariae and genetically from spirorchiids with available sequences (16–19%), grouping in the phylogenetic tree with freshwater North American species. This is the first report of freshwater spirorchiids in South America and the first molecular confirmation of the involvement of a caenogastropod in the life cycle of spirorchiids.

Graphical abstractMolecular sequences of larval trematodes reveal of the occurrence of freshwater species of turtle blood flukes (Spirorchiidae) in South America.Figure optionsDownload full-size imageDownload as PowerPoint slide