Spermiogenesis and spermatozoon ultrastructure of the davaineid cestodeRaillietina micracantha(Fuhrmann, 1909)

Spermatozoon ultrastructure of Thysanotaenia congolensis (Cyclophyllidea, Anoplocephalidae, Inermicapsiferinae): phylogenetic implications

The mature spermatozoon of Thysanotaenia congolensis, an intestinal parasite of black rat Rattus rattus from Cape Verde, is described by means of transmission electron microscopy. The ultrastructural organization of the sperm cell of T. congolensis follows Levron et al.'s type VII of the Eucestoda. It corresponds to a uniflagellate spermatozoon that presents crested bodies, periaxonemal sheath and intracytoplasmic walls, spiralled cortical microtubules and nucleus spiralled around the axoneme. These characteristics are also present in the spermatozoa of other inermicapsiferines and differ from the characters found in species belonging to the remaining subfamilies of anoplocephalids, namely Anoplocephalinae, Linstowiinae and Thysanosomatinae. Several authors consider the family Anoplocephalidae as a polyphyletic group, and its relationships with the Davaineidae are a matter of controversy. The phylogenetic implications of spermatological ultrastructural features present in inermicapsiferines and in the remaining anoplocephalids are discussed, and the available data on anoplocephalids are compared to similar results in davaineids in order to contribute to a better knowledge of relationships between these cyclophyllidean families.

Spermiogenesis and spermatozoon ultrastructure of the paruterinid cestode Notopentorchis sp. (Cyclophyllidea)

Ultrastructural characters of the spermiogenesis and mature spermatozoon of Notopentorchis sp. (Cestoda, Cyclophyllidea, Paruterinidae), a parasite from Apus affinis (Aves, Apodiformes, Apodidae) from Gabon, are described by means of transmission electron microscopy. Cytochemical analysis for detection of glycogen was applied. Vestigial striated roots associated with the two centrioles are present in the zone of differentiation. The spermiogenesis is characterized by an external growth of free flagellum followed by a proximodistal fusion of the latter with cytoplasmic protrusion, thus, corresponding to the cestode spermiogenesis of the type III pattern described by Bâ and Marchand (Mem. Mus. Natl. Hist. Nat. 166:87-95, 1995). In the final stage of spermiogenesis, a single crested body appears at the base of the forming spermatozoon. The mature spermatozoon of Notopentorchis sp. is filiform and tapering at both extremities. It consists of five regions differing in their ultrastructural characteristics. The anterior extremity of the mature spermatozoon is characterized by the presence of an apical cone and a single crested body. The cytoplasm contains one axoneme of 9 + "1" type of the trepaxonematan Platyhelminthes, a periaxonemal sheath, a layer of twisted cortical microtubules, transverse intracytoplasmic walls, and granules of glycogen. The nucleus is coiled in spiral around the axoneme. The posterior extremity of the spermatozoon is characterized by the presence of electron-dense material. This structural organization corresponds to the morphology of cestode spermatozoon of type VII as defined by Levron et al. (Biol Rev 85: 523-543, 2010). The comparison of the results with those of the two previous studies on paruterinids suggests that several characters of the spermiogenesis and the mature spermatozoon are invariable, i.e. the type III spermiogenesis and the presence of vestigial striated roots, a single crested body, a periaxonemal sheath, and intracytoplasmic walls. The main differences of the sperm cells among members of this family are the lack of dense granules (as in Triaenorhina rectangula) and the presence of electron-dense material in the posterior extremity of the spermatozoon (as in Notopentorchis sp.).

Ultrastructure of spermatogenesis of Taenia taeniaeformis (Batsch, 1786) (Cestoda, Cyclophyllidea, Taeniidae) and comparison of spermatological characters in the family Taeniidae Ludwig, 1886

The ultrastructure of spermatogenesis of Taenia taeniaeformis is described for the first time by means of transmission electron microscopy (TEM). Mature testes contain all stages of spermatogenesis; primary spermatogonia are usually situated at the periphery and mature spermatozoa in the centre of testes. The general process is similar to that described in other cestodes. Six incomplete, synchronic cytokineses occur: four mitotic and two meiotic cell divisions. All these divisions occur simultaneously, resulting in a rosette cluster of four tertiary spermatogonia, then eight quaternary spermatogonia, and subsequently sixteen primary spermatocytes. All of these enter into a growth period and their enlarged nuclei move to the periphery of cells of the rosettes. The first meiotic division forms thirty-two secondary spermatocytes and after the second meiotic division, there are sixty-four spermatids. Spermiogenesis in T. taeniaeformis corresponds to the Ba and Marchand’s Type 3 and begins with the formation of a differentiation zone in the form of a conical projection of cytoplasm delimited by a ring of arching membranes and surrounded by submembranous cortical microtubules. Within this area, there are two centrioles, orthogonally disposed, and vestigial striated rootlets. Only one of the centrioles develops a flagellum that grows externally to the cytoplasmic extension. Posteriorly, a flagellar rotation inferior to 90° occurs and the flagellum becomes parallel to the cytoplasmic extension. Later, the two processes fuse during the so-called proximodistal fusion. The nucleus elongates and moves into the cytoplasmic extension. In the final stage of spermiogenesis, a single crested body appears at the base of the differentiating spermatozoon. Finally, the ring of arching membranes constricts and the young spermatozoon detaches from the residual cytoplasm. Ultrastructural aspects of spermatogenesis are compared with that of other cestodes studied to date, particularly of the family Taeniidae.