Sperm characters of Timoniella imbutiforme (Digenea, Opisthorchioidea, Cryptogonimidae), a parasite of the European seabass Dicentrarchus labrax

Spermatological characteristics of the digenean Timoniella imbutiforme (Cryptogonimidae) collected from Dicentrarchus labrax (Teleostei: Serranidae) collected at the Gulf of Gabès in Chebba (Tunisia) were investigated for the first time by means of transmission electron microscopy. The ultrastructural study reveals that the mature spermatozoon of T. imbutiforme is a filiform cell, tapered at both extremities. The sperm cell exhibits the characteristics of digenean spermatozoa type IV namely two axonemes of the 9 + '1' pattern of trepaxonematan Platyhelminthes, 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 bundles of parallel cortical microtubules, maximum number of cortical microtubules in the anterior part of the spermatozoon and presence of two mitochondria. The first mitochondrion of moniliform type is composed of a mitochondrial cord with joined mitochondrial bulges. In addition, the male gamete of T. imbutiforme shows spine-like bodies and a posterior extremity with only the second axoneme. The ultrastructural characters of the spermatozoon of T. imbutiforme are compared with those of other digeneans belonging to the superfamily Opisthorchioidea.