Spermatological characters of Stephanostomum bicoronatum (Digenea, Acanthocolpidae), an intestinal parasite of the Brown meagre Sciaena umbra (Teleostei: Sciaenidae) off the Tunisian coast

The ultrastructural spermatozoon organisation of the acanthocolpid digenean Stephanostomum bicoronatum have been described by micrographs of transmission electron microscopy (TEM). Live digeneans were isolated from the digestive tract of the Brown meagre Sciaena umbra (Teleostei: Sciaenidae), obtained from artisanal fishing off the coast of La Chebba (Tunisia Mediterranean Sea). The ultrastructural study reveals that the male gamete of S. bicoronatum is a filamentous cell tapered at both extremities, which present typical characteristics of digenean spermatozoa of the type III, namely two axonemes of the 9 + ‘1’ pattern of trepaxonematan Platyhelminthes, nucleus, one mitochondrion, external ornamentation of the plasma membrane associated with cortical microtubules and located in the posterior part of the anterior region of the sperm cell, two parallel bundles of cortical microtubules, and maximum number of cortical microtubules in the anterior part of the spermatozoon. In addition, the male gamete of S. bicoronatum shows spine-like bodies, a large amount of glycogen granules and a posterior extremity containing only the nucleus. The results are compared and discussed according to the existing data in other digeneans, particularly with those of the family Acanthocolpidae.