Spermatological characters of the digenean Lecithostaphylus retroflexus (Molin, 1859) (Microphalloidea: Zoogonidae), a parasite of the teleost fish Belone belone gracilis

Highlights • The ultrastructural organization of the spermatozoon of the digenean Lecithostaphylus retroflexus (Microphalloidea: Zoogonidae) was described. • Indeed, alive digeneans were collected from Belone belone gracilis (Teleostei: Belonidae), caught from the Gulf of Gabès in Chebba (Tunisia). • The mature spermatozoon of L. retroflexus exhibits two axonemes of different lengths with the 9 + ‘1’ Trepaxonematan pattern, a nucleus, two mitochondria, two bundles of parallel cortical microtubules and granules of glycogen. • Additionally, the spermatozoon of L. retroflexus shows type 2 of the external ornamentation of Quilichini et al. (2011) , spine-like bodies and a continuous and submembranous layer of parallel cortical microtubules surrounding the axonemes at their anterior end. • Moreover, the morphology of the posterior spermatozoon extremity in L. retroflexus corresponds to the fasciolidean type of Quilichini et al. (2010).