Remarks on the diversity of Hysteromorpha Lutz 1931 (Digenea, Diplostomidae), with erection of a new species from South America.

Hysteromorpha Lutz, 1931 is a small but broadly distributed genus of diplostomoidean digeneans parasitic as adults primarily in cormorants, but also reported from some other fish-eating birds. Their metacercariae were found in a variety of freshwater fishes as second intermediate hosts. Prior to this study, the genus included only 3 nominal species, 2 of them distributed in the Old World and 1 in the New World. We obtained sequences of partial mitochondrial cox1 gene and nuclear rDNA operon from new specimens collected in Europe, North and South America and used them for species comparisons and phylogenetic analysis. We also examined morphology of our newly collected specimens as well as museum specimens. Our analysis has demonstrated that at least 2 (likely 3) species of Hysteromorpha are distributed in the Americas. Hysteromorpha sp. previously sequenced from larval stages, clearly represents a new species named herein Hysteromorpha ostrowskiae n. sp. Achatz, Locke et Tkach. Morphology of adults of the new species was earlier described in sufficient detail under the name Hysteromorpha triloba (Rudolphi, 1819). Our analyses also suggest the presence of another unknown Hysteromorpha sp. in North America represented by cox1 sequence from southeastern Canada (GenBank JF769473), but no morphological vouchers are available for this species.