Adult nematodes of Heliconema commonly occur in the digestive tract of fishes of the orders Anguilliformes and Synbranchiformes; but some species also can parasitize snakes.During a series ofhelminthological survey of Chinese marine fishes,large numbers of Spiruroidea nematodes were collected from the yellow pikE-conger Uroconger lepturus (Richardson) (Anguilliformes: Congridae),daggertooth pikE-conger Muraenesox cinereus (Forsskal) and the Indian pike conger Congresox talabonoides (Bleeker) (Anguilliformes: Muraenesocidae) in the South China Sea.Their examination using light microscopy and scanning electron microscopy revealed the present material represented a described species of the genus Heliconema.We named it as Heliconema hainanensis sp.n.,which refers to the typE-locality,Hainan Island.The new species differs from its congeners of Heliconema by the morphology ofpseudolabia,the number and arrangement of caudal papillae (4 pairs ofpedunculate precloacal arranged in 2 groups of 2 and 2 pairs,and 6 pairs ofpedunculate postcloacal arranged in 4 groups of 1,2,1,and 2 pairs),the length of spicules [left spicule 0.51-0.69 mm long,right spicule 0.20-0.27 mm long,spicule (right: left) ratio 1:2.20-2.69] and the morphology of female tail tip.In addition,the specimens of the new species collected from the three different hosts,together with the specimens ofHeliconema sp.collected from U.lepturus,were characterised using molecular methods by sequencing the internal transcribed spacer (ITS) of the ribosomal DNA.Analyses and comparison of the ITS sequence ofHeliconema hainanenisi sp.nov.with Heliconema sp.seem to support the validity of the new species based on the morphological observation.An identification key to the species of Heliconema was also provided.The present study also represents a substantial step toward integrating morphological and molecular data for accurate identification and delimitation species of this poorly known group.