Morphological and molecular characterization of Cucullanus bourdini Petter et Le Bel, 1992 (Ascaridida: Cucullanidae) from the yellowback fusilier Caesio xanthonota Bleeker (Perciformes: Caesionidae).

The detailed morphology of Cucullanus bourdini Petter et Le Bel, 1992 was further studied using both light and scanning electron microscopy, based on specimens collected from the yellowback fusilier Caesio xanthonota Bleeker (Perciformes: Caesionidae) from off the Taiwan Strait. In addition, C. bourdini was characterized genetically for the first time using molecular approaches by sequencing and analysing ribosomal [small ribosomal subunit (18S rDNA) and internal transcribed spacer 2 (ITS-2)] and mitochondrial [cytochrome c oxidase subunit 1 (cox1)] target regions. The molecular analysis of C. bourdini displayed no nucleotide differences in the 18S sequences, but detected 0.20-2.82% and 0.52-1.04% nucleotide divergence in the ITS-2 and cox1 regions, respectively. The new morphological and genetic data obtained herein would enable us to identify this hitherto little known species more rapidly and accurately.