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Abstract: This study presents the ultrastructure of the mature spermatozoon of Prosorchis palinurichthi (Digenea: Hemiuroidea: Sclerodistomidae), parasite of the digestive tract of the teleost fish Schedophilus velaini (Sauvage, 1879) (Centrolophidae) captured in the Atlantic Ocean, near Dakar (Senegal). This is a first report of P. palinurichthi from Senegal and from this host species. The mature spermatozoon of P. palinurichthi is filiform, tapered at both ends and exhibits the general pattern described in the hemiuroids: two axonemes of the 9+‘1’ pattern of trepaxonematans, a nucleus, a mitochondrion, external ornamentation of the plasma membrane in the anterior region of the spermatozoon and parallel cortical microtubules disposed in one side of the spermatozoon except in the anterior spermatozoon extremity and in the mitochondrial region. However, the particularities of the spermatozoon of P. palinurichthi are the presence of cortical microtubules at the anterior extremity, a great number of cortical microtubules (up to 25) in the region II of the spermatozoon, an elongate nucleus longer than the mitochondrion and the absence of spinelike bodies. Our results are discussed in context with those of previous studies in the Digenea in general and particularly in the Hemiuroidea. [Copyright &y& Elsevier]

The present study describes the ultrastructure of the mature spermatozoon of Lecithocladium excisum (Rudolphi, 1819) (Digenea: Hemiuroidea: Hemiuridae) from the stomach of the marine teleost Scomber japonicus Houttuyn (Scombridae) captured in the Atlantic Ocean, off Dakar (Senegal). The ultrastructural organization of the spermatozoon of L. excisum follows the general model described in most digeneans. It presents two axonemes of the 9+'1' pattern of the Trepaxonemata, nucleus, mitochondrion and parallel cortical microtubules, among other characters. However, some particularities of the spermatozoon of L. excisum are (i) the presence of a membranous ornamentation not associated with cortical microtubules in its anterior extremity, (ii) the presence of a very reduced number of cortical microtubules located only in the ventral side of the spermatozoon and (iii) the absence of several structures described in most digeneans such as spine-like bodies and cytoplasmic expansions.

The spermiogenesis process in Wardula capitellata begins with the formation of a differentiation zone containing two centrioles associated with striated rootlets and an intercentriolar body. Each centriole develops into a free flagellum orthogonal to a median cytoplasmic process. Later these flagella rotate and become parallel to the median cytoplasmic process, which already exhibits two electron-dense areas and spinelike bodies before its proximodistal fusion with the flagella. The final stage of the spermiogenesis is characterized by the constriction of the ring of arched membranes, giving rise to the young spermatozoon, which detaches from the residual cytoplasm. The mature spermatozoon of W. capitellata presents most of the classical characters reported in digenean spermatozoa such as two axonemes of different lengths of the 9 + "1" trepaxonematan pattern, nucleus, mitochondrion, two bundles of parallel cortical microtubules and granules of glycogen. However, some peculiarities such as two lateral expansions accompanied by external ornamentation of the plasma membrane and spinelike bodies characterize the mature sperm. Moreover, a new spermatological character is described for the first time, the so-called cytoplasmic ornamented buttons.