Morphological variability of Dicrogaster contracta Looss, 1902 (Digenea: Haploporidae) and its proposed synonymy with D. perpusilla Looss, 1902.

Dicrogaster contracta and D. perpusilla were originally described about 100 years ago from the thicklip grey mullet Chelon labrosus. Subsequent studies have reported D. contracta in several mullet species in the Mediterranean, Azov and Caspian Seas, but D. perpusilla has never been reported again. Since previous evidence suggests that the distinguishing features between these two species are uncertain, this study provides new and additional data on the variability of morphometric and meristic characters of D. contracta in order to assess their usefulness for differentiating this species from D. perpusilla. Body measurements, egg counts and shape statistics of three sets of specimens of D. contracta from different hosts and localities were compared with similar information from previous studies, including the original descriptions of D. contracta and D. perpusilla. The results showed consistent differences between the three sets in metric measurements, egg counts and shape statistics. In addition, the values of morphometric and meristic characters of D. perpusilla fell within the range of variation recorded for D. contracta. Neither conventional body measurements, eggs counts, nor shape statistics seemed useful to distinguish D. contracta from D. perpusilla, suggesting that they represent the same species. Accordingly, the valid designation of the species should be D. perpusilla because it is the type-species of the genus. This study proposes a neotype for D. perpusilla, since no type-specimens seem to be available, and provides additional morphologic data that might be useful for diagnosis of the genus Dicrogaster.