A Re-Evaluation of Zygocotyle (Digenea, Paramphistomoidea) Based on New Genetic Data Supports Its Synonymization with Wardius

The Zygocotylidae Ward, 1917 is a compact family of amphistome digeneans that until now comprised 2 genera, each represented by a single species: Zygocotyle lunata (Diesing, 1836) Stunkard, 1916 and Wardius zibethicus Barker and East, 1915 in Barker 1915. Despite highly similar morphology, these genera are separated based on the presence (Zygocotyle) or absence (Wardius) of posterolateral projections (=lappets) on the ventral sucker and esophageal bulb. In the present study, we generated partial large ribosomal subunit (28S), internal transcribed spacer 2 (ITS2) rDNA, and cytochrome c oxidase subunit 1 (COI) sequences of Z. lunata from several hosts (12 avian and 1 rodent species) throughout North and South America as well as 28S and COI sequences of W. zibethicus from muskrat in North America. The newly generated 28S sequences were used for sequence comparison and phylogenetic analysis. The COI sequences were used for species-level comparisons. Our analysis revealed a close relationship and high sequence similarity between Z. lunata and W. zibethicus. Considering the low morphological and genetic differences, we synonymize ZygocotyleStunkard, 1916 with Wardius Barker and East, 1915 in Barker 1915 and transfer Z. lunata to Wardius as Wardius lunatus (Diesing, 1836) n. comb.