Dactylostomum brayi n. sp. (Trematoda: Opecoelidae) from the Fish Hemibagrus nemurus (Bagridae) in Khun Thale Swamp, Thailand

During a parasitological survey of freshwater fishes from Khun Thale Swamp, Surat Thani Province, Thailand, a new species of opecoelid trematode, Dactylostomum brayi n. sp., was recovered from the intestine of the Asian redtail catfish Hemibagrus nemurus (Bagridae). Of the 1065 fishes examined, representing 33 species, 27 genera, and 16 families, the parasite was found exclusively in H. nemurus, with a prevalence of 27.27% and a mean intensity of 2.33 worms per infected host, suggesting a high degree of host specificity. The new species differs from all recognised freshwater congeners in the number of ventral sucker papillae, body proportions relative to the oral sucker, and the morphology of the reproductive organs. This represents the second record of Dactylostomum from Thailand, following specimens identified as Dactylostomum sp. by R. A. Bray from the same host and deposited in the Natural History Museum, London, in 1983. The present study also provides the first molecular characterisation (18S, ITS2, and 28S rRNA) for the genus Dactylostomum and reveals a close phylogenetic relationship with Dimerosaccus. These findings contribute to the taxonomy and distribution of Dactylostomum and provide a basis for future systematic and phylogenetic studies of this poorly known genus.