Morphological and molecular characterization of Raphidascaris (Ichthyascaris) lophii (Wu, 1949) (Nematoda, Anisakidae) from marine fishes from China, with a key to the species of the subgenus Ichthyascaris

The little known ascaridoid nematode Raphidascaris (Ichthyascaris) lophii (Wu, 1949) is redescribed and illustrated based on newly collected specimens from the five different marine fishes: Lophius litulon (Jordan) (Lophiiformes: Lophiidae), Lophiomus setigerus (Vahl) (Lophiiformes: Lophiidae), Antennarius hispidus (Bloch et Schneider) (Lophiiformes: Antennaridae), Zeus faber Linnaeus (Zeiformes: Zeidae) and Ostichthys japonicus (Cuvier) (Beryciformes: Holocentridae) from the East and South China Sea. This species differs from all congeners in the subgenus Ichthyascaris by the length of the ventricular appendix (0.52–0.98 mm long), the number and arrangement of caudal papillae (26–32 pairs of precloacal, 3–4 pairs of paracloacal and 8–11 pairs of postcloacal) and the length of the spicules (0.49–0.88 mm long, representing 3.08–4.70% of body length). In addition, nematodes collected from these five different fishes have been characterized using molecular methods by sequencing and analysing the internal transcribed spacer (ITS) of ribosomal DNA. No variation in size and nucleotide polymorphisms is detected within the target sequence among all samples analysed. These data contribute to facilitate an accurate diagnosis of this poorly known nematode. An identification key to the species of the subgenus Ichthyascaris is also provided.