First Molecular Data for Trematode Bianium tonkinensis Nguyen, Nguyen, Ha, Ermolenko, 2017 (Digenea: Lepocreadiidae) from Vietnam and the Problem of Paraphyly of the Genus Bianium

Adult worms of the genus Bianium (Lepocreadiidae) were collected from the intestines of fish Lagocephalus lunaris from the coastal waters of Cat Ba Island, Vietnam. Species identification and validation of these trematodes based on morphological and molecular datasets with the analysis of phylogenetic relationships within the Lepocreadiidae were carried out. The morphological characteristics of the worms from our study agree with the diagnosis of the genus Bianium and most similar morphologically to B. tonkinensis from Vietnam based on comparative analysis of our material with type material, published earlier. Based on molecular data (ITS2 and 28S rDNA), trematode from our material is close to several lepocreadiid species, namely B. arabicum, and Diploproctodaeum monstrorum from Australia by p-distance values at the interspecific level. Results of phylogenetic analysis show that the genus Bianium is paraphyletic, confirming results of earlier studies. Trematodes from our study belong to the species Bianium tonkinensis. The taxonomical status of B. arabicum from New Caledonia is still questionable. We support the statement that the Australian trematode, misidentified earlier as B. plicitum, is unknown species, which presumably belong to the genus Bianium.