Opegaster plateen n. sp. (Digenea: Opecoelidae) from the giant mudskipper Periophthalmus schlosseri (Pallas, 1770) (Perciformes: Gobiidae) from Thailand

Abstract Mudskippers (Oxudercinae) are amphibious gobioid fishes inhabiting intertidal and mangrove ecosystems throughout the Indo–West Pacific region. Despite their ecological importance, information on their helminth fauna remains scarce. During a survey of parasites infecting the giant mudskipper, Periophthalmodon schlosseri (Pallas, 1770), in Chumphon Province, Thailand, specimens of an undescribed species of Opegaster Ozaki, 1925 (Opecoelidae) were recovered from the intestine. The species is described herein as Opegaster plateen n. sp. on the basis of morphological and molecular evidence. The new species is characterized by a relatively large ventral sucker bearing 5–6 papillae on each lip, lobulated tandem testes, a lobulated pretesticular ovary and a combination of morphometric characters that distinguish it from all previously described congeners, including O. ouemoensis , the only species previously reported from a mudskipper host. Phylogenetic analyses based on partial 18S and 28S rRNA gene sequences and the mitochondrial cytochrome c oxidase subunit I ( cox1 ) gene supported the placement of O. plateen n. sp. within the Opecoelinae. In both the 28S and cox1 phylogenies, the new species showed a close relationship with Opegaster mezcal and Opecoelus adsphaericus . The sequences generated in the present study represent only the second molecular data obtained from a species of Opegaster and the first from a mudskipper. This study expands current knowledge of the diversity of digenean trematodes associated with intertidal fishes and highlights the limited state of knowledge of the parasite fauna of mudskippers.