Spermiogenesis and sperm ultrastructure of two species of Duthiersia, parasites of monitors, with a review of spermatological characters in the Diphyllobothriidea (Cestoda)

Abstract

The present study compares the spermiogenesis of two species of the diphyllobothriidean cestodes (family Scyphocephalidae), Duthiersia expansa and Duthiersia fimbriata, parasites of Asian and African monitors (Varanus spp.), and establishes the ultrastructural organization of the spermatozoon of D. fimbriata. The spermatids of both species are similar and exhibit a differentiation zone containing two centrioles and electron-dense material in the apical region. The centrioles are separated from one another by an intercentriolar body and each is associated with a striated root. During the early stage of spermiogenesis, the centrioles form two flagella that grow orthogonally to the median cytoplasmic process. The orthogonal development is followed by a flagellar rotation and proximodistal fusion with median cytoplasmic process. The mature spermatozoon of D. fimbriata is characterized by the presence of two axonemes presenting the type 9+“1” trepaxonematan pattern, parallel cortical microtubules and a nucleus. The most interesting finding is confirmation of the absence of a crested body in the anterior extremity of the gamete, which seems to be a typical feature of all diphyllobothriideans. This observation contradicts the previous information on D. fimbriata provided by Justine (1986), who reported the crested body for the species. The pattern of spermiogenesis of scyphocephalids, represented by two species of Duthiersia, is similar to that in members of the Diphyllobothriidae. The existing data on species of all three families of the Diphyllobothriidea are reviewed and it is shown that the main characters of the sperm cell typical of these cestodes resemble those of other basal groups of tapeworms, which represents another support of their ancestral position.