A new species of genus Hysterothylacium Ward & Magath, 1917 (Nematoda: Ascaridoidea) from the greater amberjack Seriola dumerili (Risso) (Carangiformes: Carangidae) in the Persian Gulf off Iraq.

A new ascaridoid nematode, Hysterothylacium malleocaudatum sp. n., was described using both light and scanning electron microscopy, based on specimens collected from the greater amberjack Seriola dumerili (Risso) (Carangiformes: Carangidae) in the Persian Gulf off Iraq. The new species can be distinguished from the congeners by the combination of the following features, the presence of remarkable lateral alae starting from base of ventro-lateral lips, the short intestinal caecum and long ventricular appendix (intestinal caecum representing 21.1-40.5% of oesophageal length, ratio of intestinal caecum to ventricular appendix 1: 1.42-3.77), the relatively long oesophagus (oesophageal length representing 9.83-14.3 % body length), the number and arrangement of the caudal papillae (31-37 pairs precloacal, 1-2 pairs paracloacal and 6 pairs postcloacal), and the presence of inflated hammer-shaped tail tip in both sexes. The new species represents the fourth Hysterothylacium species reported in marine fishes from Persian Gulf, off Iraq.