Ultrastructure of the spermatozoon of Labracetabulum gephyroberici (Digenea, Opecoelidae) intestinal parasite of Gephyroberyx darwinii (Teleostei, Trachichtyidae) in Senegal

Abstract

This work is the first ultrastructural study of spermatozoa in a species of Digenea belonging to the genus Labracetabulum. Labracetabulum gephyroberici parasitizes the digestive tract of the teleost fish Gephyroberyx darwinii (Trachichtyidae) captured in the Atlantic Ocean near Dakar (Senegal). This is also the first report of L. gephyroberici from Senegal. The mature spermatozoon is filiform tapered at both ends and exhibits the general organization described in most Opecoelideans, namely two axonemes of the 9 + “1” pattern of the Trepaxonemata, an anterior electron-dense material, an external ornamentation associated with a row of cortical microtubules, spine-like bodies, two mitochondria and two bundles of cortical microtubules. However, the mature spermatozoon of L. gephyroberici exhibits some particularities: a short first axoneme which does not reach the nuclear region and the position of the second mitochondrion which reaches almost the posterior part of the mature spermatozoon. The second mitochondrion is still present after the disappearance of the second axoneme. The morphology of the posterior extremity corresponds to the Opecoelidean type described by Quilichini et al. (2010).