Nudaciraxine imperium sp. n. (Monogenea: Axinidae) from the gills of Mediterranean needlefish Tylosurus acus imperialis (Teleostei: Belonidae).

Nudaciraxine imperium sp. n. (Monogenea: Axinidae) is described from the gills of the needlefish Tylosurus acus imperialis (Rafinesque) caught in the Gulf of Gabès, Tunisia. This new species mainly differs from both previously described species, Nudaciraxine gracilis (Linton, 1940) Price, 1962 from Strongylura marina (Walbaum) and Nudaciraxine cabosanlucensis Payne, 1990 from Ablennes sp., by having more testes (42 vs. 20-22 and 32, respectively). Nudaciraxine imperium also differs from N. gracilis by having a median vaginal pore (submedian in N. gracilis), narrower clamps (52-70 microm vs. 75-100 microm) and differently shaped haptoral lateral hamuli. From N. cabosanlucensis it can be distinguished by a J-shaped rather than U-shaped ovary, a longer cirrus pouch (125-190 microm vs. 64-70 microm), an oesophageal bifurcation slightly anterior to genital complex (immediately after pharynx in N. cabosanlucensis) and a wider guard on the lateral hamuli. In agreement with Payne (1990), the diagnosis of the genus Nudaciraxine Price, 1962 is amended as follows: vaginal pore dorsal, median to submedian, armed or not with horn-like spines. This is the first report of the genus Nudaciraxine in the Mediterranean Sea. The potential use of axinid monogeneans as biological tags for subspecies of belonid fishes is discussed.