Cucullanus bulbosus (Lane, 1916) Barreto, 1918 (Nematoda, Cucullanidae) from the common ponyfish Leiognathus equulus (Leiognathidae): Morphology and molecular study

The common ponyfish Leiognathus equulus is a marine fish species with very high commercial value. Little information is available about its parasitic infections. Based on light and scanning electron microscopy, as well as sequencing and analysis of the partial regions of the ITS-1, 18S rRNA, COX1 genes, were employed for the systematic evaluation of a nematode parasite, which it first isolated from L. equulus in Jeddah Province, Red Sea, Saudi Arabia. Results revealed that this nematode parasite closely resembles the previously described Cucullanus bulbosus. Microscopic examination showed that it distinguished from congeners by the unique structure of hemispherical elevation at pseudobuccal capsule level, the ratio of esophagus/body length, spicules size, presence of pre-cloacal sucker, rod-shaped gubernaculum, and the arrangement of caudal papillae in males. Phylogenetic analyses based on ITS-1, 18S rRNA, and COX1 gene regions were constructed to investigate phylogenetic relationships between this parasite species and other related taxa. Results supported that Cucullanus bulbosus resembles a sister of Cucullanus genypteri, Cucullanus pulcherrimus, Cucullanus bourdini, Cucullanus extraneus, and Cucullanus hainanensis by using different genetic markers. This study provides more information about combining morphological and molecular data to identify Cucullanus species with the first natural occurrence in the common ponyfish inhabited in Saudi Arabia. •Natural occurrence of Cucullanus species in the common pony fish.•Useful knowledge obtained to confirm the existence of Cucullanus bulbosus.•This parasite has new host species and geographical records in Saudi Arabia.