Restoration of the Genus Paraunisaccoides Martin, 1973 (Digenea: Haploporidae) and Description of P. elegans n. sp. and Unisaccus halongi n. sp. from Mugilid Fish in Vietnam

Abstract

We restore the genus Paraunisaccoides (Haploporidae), synonymised earlier with the genus Skrjabinolecithum. Adult worms, detected in Vietnamese mullet fish, were highly similar to trematodes described as P. lobolecithum via digestive and genital system structures and relative organ arrangement. Differences are expressed as absence and presence of pads on the hermaphrodite duct, respectively, and the disjunction of some metric parameter values, namely body, ovary and eggs. Ribosomal DNA sequences, based on the phylogenetic analysis of Haploporidae, indicates that new worms represent a sister clade to Unisaccus tonkini. Genetic divergence between new worms and Skrjabinolecithum species can be interpreted as intergeneric. Based on morphological and molecular data, we recognise Paraunisaccoides as a valid genus within Waretrematinae and worms from Vietnam as a new species of this genus, P. elegans n. sp. Other worms detected in Vietnamese mugilids are morphologically similar to representatives of Paraunisaccoides и Skrjabinolecithum. However, molecular-based phylogenetic analysis showed that these trematodes are closely related to Unisaccus tonkini; the genetic divergence between them is at the interspecific level, despite considerable differences in vitellarium structure as intergeneric character. Accepting the priority of molecular results, we include these new worms into the genus Unisaccus as new species, Unisaccus halongi n. sp.