Morphological and molecular evidence for a new species of the genus Dichelyne Jägerskiöld, 1902 (Ascaridida: Cucullanidae) from marine perciform fishes in the South China Sea.

A new cucullanid nematode, Dichelyne (Dichelyne) breviculus n. sp., collected from the intestine of the goatee croaker Dendrophysa russelii (Cuvier) (Perciformes: Sciaenidae), the burrowing goby Trypauchen vagina (Bloch & Schneider) and the tropical sand goby Acentrogobius caninus (Valenciennes) (Perciformes: Gobiidae) in the South China Sea, is described using both light and scanning electron microscopy. The new species differs from its congeners in the size of body (2.16-2.96 mm in male), the position of the excretory pore and deirids, the length of the spicules (0.90-1.32 mm, representing 32.4-51.9% of body length), the arrangement of the caudal papillae and the morphology of the tail. In addition, in order to primarily assess the validity of the new species genetically, the specimens of D. breviculus n. sp. collected from the three different hosts were also characterised using molecular methods by sequencing and analysing ribosomal [small ribosomal subunit (18S rDNA) and internal transcribed spacer (ITS)] and mitochondrial [cytochrome c oxidase subunit 1 (cox1)] target regions. The molecular analyses support the validity of the new species based on the morphological observations.