Ultrastructure of spermiogenesis and the spermatozoon of Raillietina (raillietina) tunetensis (Cyclophyllidea, Davaineidae), intestinal parasite of turtle doves in Senegal

Abstract

Spermiogenesis in Raillietina (Raillietina) tunetensis begins with the formation of a differentiation zone equipped with cortical microtubules and containing two centrioles. One of the centrioles very rapidly gives rise to a flagellum which fuses with a median cytoplasmic extension, the cortical microtubules elongate and arched membranes appear. After the migration of the nucleus two crest-like bodies form and the old spermatid becomes detached from the residual cytoplasm. The mature spermatozoon of R. (R.) tunetensis exhibits an apical cone of electron-dense material and two helicoidal crest-like bodies 100 to 200 nm thick. The cortical microtubules are spiralized and make an angle of about 60° to the spermatozoon axis. The axoneme is of the 9 + “1” pattern and does not reach the posterior extremity of the gamete. The nucleus is a fine, compact cord wound in a spiral which may make as much as two complete coils round the axoneme. The cytoplasm is electron-dense in region V of the spermatozoon. Over the rest of the gamete it is made up of lucent material divided into irregular compartments by electron-dense material. The latter consists of a fine, discontinuous peri-axonemal sheath, a fine granular sub-microtubular layer situated in regions I and II, and irregularly spaced partitions localized in regions III and IV. A nucleus with an annular cross section has never been described in a cestode spermatozoon; nor have two crest-like bodies of different length and thickness. In addition we report for the first time the existence of crest-like bodies in the Davaineidae.