The ultrastructure of the mature spermatozoon and the spermiogenesis of a cestode belonging to the family Metadilepididae is described for the first time. The mature spermatozoon of Skrjabinoporus merops is characterized by twisted peripheral microtubules, the presence of a single crested body, periaxonemal sheath and electron-dense rods, and the absence of intracytoplasmic walls and inclusions (glycogen or proteinaceous granules); no peripheral microtubules where nucleus contacts the external plasma membrane. Four morphologically distinct regions of the mature spermatozoon are differentiated. The proximal part (Region I) contains a single crested body, periaxonemal sheath is absent in some (proximal) sections and is present in others situated closer to the nucleus. The central Region II is nucleated, and is followed by Region III that contains a periaxonemal sheath. The distal pole, Region IV, is characterized by disintegration of the axoneme. Spermiogenesis follows the type III pattern (Bâ and Marchand 1995) although in S. merops a slight flagellar rotation is observed. The differentiation zone is characterized by the absence of striated roots and intercentriolar body; two centrioles are present, one of which gives rise to a free flagellum. The latter rotates and undergoes proximodistal fusion with the cytoplasmic protrusion of the differentiation zone. Spermiological characters of S. merops are similar to those of the families Taeniidae and Catenotaeniidae. The mature spermatozoon differs from those of the Dilepididae (where the metadilepidid species have previously been classified) by the lack of glycogen.

Yoneva, A., Georgieva, K., Mizinska, Y., Nikolov, P. N., Georgiev, B. B. and Stoitsova, S. R. 2010. Ultrastructure of spermiogenesis and mature spermatozoon of Anonchotaenia globata (von Linstow, 1879) (Cestoda, Cyclophyllidea, Paruterinidae). -Acta Zoologica (Stockholm) 91: [184][185][186][187][188][189][190][191][192] The ultrastructure of spermiogenesis and of the spermatozoon of a species of the family Paruterinidae is described for the first time. The spermiogenesis of Anonchotaenia globata starts with the formation of a differentiation zone with two centrioles associated with thin striated roots. One of the centrioles gives rise to a free flagellum followed by a slight flagellar rotation and a proximodistal fusion of the flagellum with the cytoplasmic protrusion. This pattern corresponds to Type III spermiogenesis in cestodes. The spermatozoon consists of five distinct regions. The anterior extremity possesses an apical cone and a single helically coiled crested body. The cortical microtubules are spirally arranged. The axoneme is surrounded by a periaxonemal sheath and a thin layer of cytoplasm filled with electron-dense granules in Regions I-V. The periaxonemal sheath is connected with the peripheral microtubules by transverse intracytoplasmic walls in Regions III and IV. The nucleus is spirally coiled around the axoneme. Anonchotaenia globata differs from Dilepididae (where paruterinids have previously been classified) in the type of spermiogenesis, the lack of glycogen inclusions and the presence of intracytoplasmic walls. The pattern of spermiogenesis is similar to that in Metadilepididae and Taeniidae, which are considered phylogenetically close to Paruterinidae.

The ultrastructure of the spermiogenesis of a dilepidid cestode species is described for the first time. The spermiogenesis of Angularella beema is characterised by absence of both flagellar rotation and proximodistal fusion. The differentiation zone is surrounded by cortical microtubules and is delimited by a ring of arching membranes. It contains two centrioles, one of which develops the axoneme that grows directly into the elongating cytoplasmic protrusion. This pattern of spermiogenesis was described as the Type IV spermiogenesis of cestodes. Among cestodes, similar pattern of spermiogenesis is known in the family Hymenolepididae and in some representatives of the family Anoplocephalidae. The mature spermatozoon of A. beema consists of five regions differing in their ultrastructural characteristics. It is characterised by the presence of cortical microtubules (spirally arranged at angle of 30-40° to the spermatozoon axis) and a single crested body. There is a periaxonemal sheath in certain parts of the spermatozoon as well as glycogen-like granules between the periaxonemal sheath and the cortical microtubules. The comparisons of the mature spermatozoon of A. beema with those of other two dilepidid species (Dilepis undula and Molluscotaenia crassiscolex) demonstrate some variation within the family: presence of periaxonemal sheath in A. beema and D. undula and its absence in M. crassiscolex; presence of electron-dense rods in D. undula and their absence in A. beema.

Ultrastructural characters of spermiogenesis and mature spermatozoon of Triaenorhina rectangula (Fuhrmann, 1908) are examined by transmission electron microscopy. Spermiogenesis follows the Bâ and Marchand's Type III spermiogenesis of cestodes. The process begins with the formation of a differentiation zone containing two centrioles and a cytoplasmic protrusion. The centrioles are associated with vestigial striated roots. One of the centrioles develops a free flagellum externally to the cytoplasmic protrusion. After a slight rotation, the free flagellum fuses with the cytoplasmic protrusion. In the final stage of spermiogenesis, a single crested body appears in the anterior part of the differentiating spermatozoon. The anterior extremity of the mature spermatozoon is characterised by an apical cone and a single crested body. The axoneme is of the 9+"1" trepaxonematan type. A periaxonemal sheath and electron-dense rods are described in some parts of the mature spermatozoon. The nucleus is electron-dense and spirally coiled around the axoneme. The cortical microtubules are spirally arranged at an angle of about 40° to the spermatozoon axis. The present results show that the ultrastructural characters of spermiogenesis and mature spermatozoon of T. rectangula resemble most closely those in taeniids and metadilepidids. The comparison of these results with the only previous spermiological description of a paruterinid species reveals differences relative to the occurrence of filamentous rods of electron-dense material versus intracytoplasmic walls in the mature spermatozoon that may reflect the polyphyletic character of the Paruterinidae.

This is the first ultrastructural study of the spermiogenesis and the mature spermatozoon of a cyclophyllidean cestode of the family Gryporhynchidae. The spermiogenesis of Valipora mutabilis begins with the formation of a differentiation zone delimited by arching membranes and containing two centrioles. One of the centrioles develops an axoneme that grows directly into the cytoplasmic protrusion. The other centriole remains situated in a cytoplasmic bud and is subsequently aborted (type IV of cestode spermiogenesis). The mature spermatozoon of V. mutabilis is a filiform cell, tapered at both extremities and lacks mitochondria. The anterior extremity is characterised by the presence of an apical cone and a single helicoidal crested body. The axoneme is of 9 + '1' trepaxonematan pattern, with a periaxonemal sheath. The cortical microtubules are twisted at an angle of about 45 degrees to the spermatozoon axis. The nucleus is electron dense and spirally coiled around the axoneme. The cytoplasm is electron lucent and contains numerous granules of electron-dense material. In contrast to a recent opinion for close phylogenetic relationships, these ultrastructural data demonstrate the distant position between gryporhynchids and the family Taeniidae. The most similar pattern in the ultrastructure of the spermiogenesis and the mature spermatozoon has been described for dilepidids, some hymenolepidids and some anoplocephalids.