Morphological variability and molecular characterization of Mawsonascaris australis (Johnston & Mawson, 1943) (Nematoda: Ascaridoidea: Acanthocheilidae) from the brown guitarfish Rhinobatos schlegelii Müller & Henle (Rhinopristiformes: Rhinobatidae).

A rare ascaridoid species, Mawsonascaris australis (Johnston & Mawson, 1943), is reported from the Taiwan Strait for the first time, and the brown guitarfish Rhinobatos schlegelii Müller & Henle (Rhinopristiformes: Rhinobatidae) represents a new fish host. The detailed morphology of M. australis was studied using light and scanning electron microscopy (SEM) based on the newly collected specimens. The results revealed some important, but previously unreported or erroneous, morphological features, including the lateral alae starting well posterior to the base of the ventrolateral lips, the presence of one pair of double paracloacal papillae and a single, small precloacal median papilla on the anterior margin of the cloaca. In addition, in order to determine whether the morphometric difference in the relative lengths of the right and left spicules represents intraspecific or interspecific variation, specimens of M. australis were characterized using molecular approaches by sequencing and analysing the ribosomal internal transcribed spacer (ITS) and mitochondrial cox1 genes. The results indicate that this morphometric difference represents intraspecific variability.