Digenetic trematodes from siganid fish Amphacanthus sigan at Macady Bay, Southern Hurghada, Red Sea, Egypt

Forty fish samples of Amphacanthus sigan were collected from Sharm El-Naga southern Hurghada to study the parasitic infection included and present a new individual to Helicometra species using light microscope and re-describe another digenean trematode species using scanning electron microscope (SEM). Two trematode species were identified and described; Helicometra siganus n. sp. Nov belonging to Helicometra Odhner, 1902 (family Opecoelidae Ozaki, 1925) which is different from all the listed species in many features as having an elongated body, tapering anteriorly and larger sucker ratio; the vitellaria extended from the intestinal bifurcation to the posterior extremity of the hind-body and finally the cirrus sac and cirrus longer than the other species and extended to the midpoint of esophagus level. So, these criteria are specific and sufficient to consider it as a new species. The other species, Gyliauchen volubilis Nagaty, 1956 (Gyliauchenidae Fuki, 1929 and Ozaki, 1933) which was described before but some other constituent are not evident and appeared using the electron microscope. However, the present sample illustrated transverse striations on the body surface, the acetabulum evaginates outward, ovoid shaped and surrounded by lip-like structures and finally, the excretory pore is situated at some distance from the acetabulum at the posterior end extremity.