Spermiogenesis and spermatozoon ultrastructure of Nicolla wisniewskii (Digenea: Opecoelidae), an intestinal parasite of brown trout Salmo trutta (Pisces: Teleostei)

Spermiogenesis and ultrastructure of spermatozoon of Nicolla wisniewskii (Digenea, Opecoelidae), an intestinal parasite of Salmo trutta, were studied by electron microscopy. Spermiogenesis follows the general pattern found in the Digenea. It begins with the formation of a differentiation zone, including striated rootlets associated with 2 centrioles and an intercentriolar body. The flagella undergo a rotation of greater than 90 degrees. Then, their fusion with the median cytoplasmic process is proximodistal and asynchronous. A peculiarity was observed before the fusion of flagella, i.e., the attachment zones joined as 2 pairs by an electron-dense bridge. The mature spermatozoon is characterized by 2 axonemes, cortical microtubules, a nucleus, 2 mitochondria, external ornamentation, and spinelike bodies. At the posterior end of flagella, the spermatozoon is also characterized by the presence of a central element of the axoneme and without the 9 microtubule doublets. These results were compared with those of the other digeneans and, in particular, with other species of Opecoelidae. It appears that the number of cortical microtubules and their localization in the spermatozoon may be an interesting feature of their phylogeny.     

Spermiogenesis and ultrastructure of the spermatozoon of the liver fluke Fasciola gigantica Cobbold, 1856 (Digenea: Fasciolidae), a parasite of cattle in Senegal

The present paper describes the spermiogenesis and the ultrastructure of the spermatozoon of Fasciola gigantica, as revealed by transmission electron microscopy. Spermiogenesis in F. gigantica begins with the formation of a differentiation zone containing 2 centrioles with associated striated roots and an intercentriolar body between them. Each centriole develops a flagellum. Proximodistal fusion of these flagella with the median cytoplasmic extension gives rise to the spermatozoon. Spermiogenesis in F. gigantica is characterized by the formation of a dorsolateral cytoplasmic expansion, an external ornamentation of the cell membrane, and spinelike bodies. These 3 structures were also observed in the anterior part of the spermatozoon. Our study describes for the first time the simultaneous presence of dorsolateral cytoplasmic expansion, external ornamentation of the plasma membrane, and spinelike bodies in the spermatozoon of a trematode.     

Spermiogenesis and spermatozoon ultrastructure of the digenean Neoapocreadium chabaudi (Apocreadiidae), a parasite of Balistes capriscus (Pisces,Teleostei)

Spermiogenesis and the ultrastructural organization of the spermatozoon of the digenean Neoapocreadium chabaudi are described by means of transmission electron microscopy.Spermiogenesis follows the usual pattern found in the digeneans. It begins with the formation of a zone of differentiation bordered by cortical microtubules, characterized by the presence of an intercentriolar body composed of seven electron-dense plates situated between two striated rootlets and two centrioles. These centrioles give rise to two free flagella. Later, both flagella undergo a rotation of 90° and fuse with the median cytoplasmic process. Spermiogenesis finishes when the ring of arched membranes constricts. The mature spermatozoon of N. chabaudi is characterized by the presence of 2 axonemes of different lengths presenting the 9 + “1” trepaxonematan pattern, 2 bundles of parallel cortical microtubules, 2 mitochondria, a nucleus, and granules of glycogen. Nevertheless, several characters such as the morphology of sperm extremities and the presence of spinelike bodies allow us to distinguish N. chabaudi from other digenetic trematodes. The present paper provides the first ultrastructural results of a digenean belonging to the family Apocreadiidae that may be useful for the understanding of digenean relationships and phylogenetic studies.     

Spermiogenesis and spermatozoon of the tapeworm Ligula intestinalis (Diphyllobothriidea): phylogenetic implications

Using transmission electron microscopy, spermiogenesis and the spermatozoon ultrastructural organization are described in Ligula intestinalis (Linnaeus, 1758) (Diphyllobothriidea), a parasite of the great crested grebe Podiceps cristatus (Linnaeus, 1758). Spermiogenesis starts with the differentiation zone of 2 striated rootlets, 2 centrioles giving rise to 2 flagella, and an intercentriolar body. The latter is composed of 5 electron-dense layers separating 4 electron-lucent layers. In the early stages of spermiogenesis, an electron-dense material is present in the apical region of the differentiation zone. Later, the flagella undergo a rotation and fuse with the cytoplasmic extension in a proximo-distal process. The spermatozoon contains 2 axonemes with a 9 + "1" trepaxonematan pattern, the nucleus, the cortical microtubules, and an electron-dense zone. The spermatozoon anterior extremity in L. intestinalis is characterized by the absence of crested bodies and a ring of electron-dense cortical microtubules. Some characters of spermiogenesis and spermatozoon in L. intestinalis confirm the recent splitting of "Pseudophyllidea" into 2 new orders, i.e., Bothriocephalidea and Diphyllobothriidea. The process of spermiogenesis is similar in both orders for the "type I" of spermiogenesis and the presence of electron-dense material. However, the intercentriolar body is clearly more developed in the Diphyllobothriidea than in the Bothriocephalidea. Moreover, these 2 orders seem to differ in the presence or absence of a ring of electron-dense cortical microtubules in the anterior extremity of the spermatozoon.     

Mesocestoides lineatus (Goeze, 1782) (Mesocestoididae): new data on sperm ultrastructure

Spermiogenesis and the ultrastructural characters of the spermatozoon of Mesocestoides lineatus are described by means of transmission electron microscopy, including cytochemical analysis for glycogen. Materials were obtained from a golden hamster (Mesocricetus auratus) after experimental infection with tetrathyridia metacestodes obtained from naturally infected lizards (Anolis carolinensis) from Louisiana. Spermiogenesis in M. lineatus is characterized by the orthogonal growth of a free flagellum, a flagellar rotation, and a proximodistal fusion. The zone of differentiation contains 2 centrioles associated with striated rootlets and a reduced intercentriolar body. The mature spermatozoon of M. lineatus lacks a mitochondrion, and it is characterized by the presence of (1) a single, spiraled, crested body 150 nm thick; (2) a single axoneme of the 9+'1' pattern of trepaxonematan Platyhelminthes; (3) a parallel and reduced row of submembranous cortical microtubules; (4) a spiraled cordon of glycogen granules; and (5) a spiraled nucleus encircling the axoneme.     

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

Miquel, J., Torres, J., Foronda, P. and Feliu, C. 2010. Spermiogenesis and spermatozoon ultrastructure of the davaineid cestode Raillietina micracantha. — Acta Zoologica (Stockholm) 91 : 212–221 The spermiogenesis and the ultrastructural organization of the spermatozoon of the davaineid cestode Raillietina micracantha are described by means of transmission electron microscopy. Spermiogenesis begins with the formation of a zone of differentiation containing two centrioles. One of the centrioles develops a free flagellum that later fuses with a cytoplasmic extension. The nucleus migrates along the spermatid body after the proximodistal fusion of the flagellum and the cytoplasmic extension. During advanced stages of spermiogenesis a periaxonemal sheath and intracytoplasmic walls appear in the spermatids. Spermiogenesis finishes with the appearance of two helicoidal crested bodies at the base of spermatids and, finally, the narrowing of the ring of arched membranes detaches the fully formed spermatozoon. The mature spermatozoon of R. micracantha is a long and filiform cell, tapered at both ends, which lacks mitochondria. It exhibits two crested bodies of different lengths, one axoneme of the 9 + ‘1’ pattern of trepaxonematan Platyhelminthes, twisted cortical microtubules, a periaxonemal sheath, intracytoplasmic walls, granules of glycogen and a spiralled nucleus. The anterior extremity of the spermatozoon is characterized by the presence of an electron‐dense apical cone and two spiralled crested bodies while the posterior extremity of the male gamete exhibits only the axoneme and an electron‐dense posterior tip.     

Spermatological characters in Diphyllobothrium latum (Cestoda, Pseudophyllidea)

Spermiogenesis and the ultrastructural features of the spermatozoon of Diphyllobothrium latum (Cestoda, Pseudophyllidea) are described using transmission electron microscopy. Spermiogenesis is characterized by the development of two flagella of unequal length that grow asynchronously. When the first growing flagellum starts to rotate, the second one develops. Flagellar rotation is thus asymmetric and asynchronic. It is followed by proximodistal fusion with the median cytoplasmic process. Electron-dense material is present in the apical region of the zone of differentiation in the early stages of spermiogenesis. The intercentriolar body consists of seven plates: three are electron-dense. Four attachment zones occur in the median cytoplasmic process. An atypical arrangement of striated roots was occasionally observed. The mature spermatozoon possesses two axonemes of 9 + "1" trepaxonematan pattern, nucleus, cortical microtubules, electron-dense granules, and lacks mitochondria. The ultrastructure of the anterior extremity of the spermatozoon in D. latum clearly differs from that in the bothriocephalid pseudophyllideans, mainly in the absence of a crested body and a ring of electron-dense tubular structures. The spermatological data support the assumption that the order Pseudophyllidea is formed by two unrelated clades, "Bothriocephalidea" and "Diphyllobothriidea."     

Spermiogenesis and the spermatozoon ultrastructure of Robphildollfusium fractum (Digenea: Gyliauchenidae), an intestinal parasite of Sarpa salpa (Pisces: Teleostei)

Spermiogenesis in Robphildollfusium fractum begins with the formation of a differentiation zone containing: two centrioles, each bearing striated rootlets, nucleus, several mitochondria and an intercentriolar body constituted by seven electron-dense layers. The two centrioles originate two free flagella growing orthogonally to the median cytoplasmic process. Later, the free flagella rotate and undergo proximodistal fusion with the median cytoplasmic process. Nuclear and mitochondrial migrations occur before this proximodistal fusion. Finally, the young spermatozoon detaches from the residual cytoplasm after the constriction of the ring of arched membranes. The spermatozoon of R. fractum exhibits two axonemes of different length of the 9 + ‘1’ trepaxonematan pattern, nucleus, two mitochondria, two bundles of parallel cortical microtubules, external ornamentation of the plasma membrane, spine-like bodies and granules of glycogen. Additionally, a shorter axoneme, which does not reach the nuclear region, the presence of an electron-dense material in the anterior spermatozoon extremity and the morphologies of both spermatozoon extremities characterize the mature sperm of R. fractum.     

Spermatogenesis in the black porgy,Acanthopagrus schlegeli (teleostei: Perciformes: Sparidae)

The ultrastructure of spermatogenesis and of the spermatozoon of Acanthopagrus schlegeli (Sparidae) are described. The testis is of the unrestricted type. Germ cells are surrounded by cyst cells. Spermiogenesis involves conspicuous modifications such as intracellular movements (diplosome and mitochondria migration, nuclear rotation, and depression) and structural changes (chromatin condensation, shape of mitochondria, and loss of cytoplasm). The mature spermatozoon has a spherical nucleus with a deep, axial nuclear fossa, and an unusual notch, shaped like a bow tie. The short midpiece contains four spherical mitochondria and encircles the basal body of the flagellum. It is concluded that the A. schlegeli spermatozoon is of a primitive type, but that it is characterized by a unique feature which may provide a useful systematic character. © 1993 Wiley-Liss, Inc.     

Implications phylogénétiques de I'ultrastructure de la spermatogenèse, du spermatozoïde et de I'ovogenèse du TurbellariéUrastoma cyprinae ("Prolecithophora", Urastomidae)

Spermiogenesis in Urastoma cyprinae (Graff. 1882) involvcs a progressive lengthening of the spermatid. Free flagella are only transitory. The mature spermatozoon is fusibrm. 45μm in length and 2.5 μm in width. It contains two incorporated axonermes of the flatworm 9+"1" pattern, two elongated mitochondria. an elongated nucleus and a row or cortical longitudinal microtubules. Observations on oogenesis concerncd only the immuturc ovary. lmmature oocytes contain few dense granules and accssory cells were not ohserved. Phylogenetic implications of a biflagellate spermatozoon in a Prolecithophora are important. The presence of two 9 +"1" axonemes confirms that Urastoma (and the Prolecithophora) belongs to the taxon Trepaxonemata Ehlers. Previous electron microscope studies on spermitozoa of Prolecithophora (four genera) only dealt with aflagellate spermatozoa. On this basis, Ehlers (1985) proposed two autapomorphics for the taxon Prolecithophora: aflagellate spermatozoon and spermatozoal mitochondrial derivatives with abundant membranes. The present observations on Urastoma contradict these two autapomorphics. The taxon Prolecithophora cannot be defined by autapomorphies of the spermatozoon.     

Reinvestigation of the ultrastructure of spermiogenesis and the spermatozoon of Hymenolepis nana (Cestoda, Cyclophyllidea), parasite of the small intestine of Rattus rattus.

Spermiogenesis in Hymenolepsis nana begins with the formation of a differentiation zone. This is limited at the front by arched membranes, is surrounded by cortical microtubules associated with 12 crested-like bodies, and contains a single centriole made up of doublets. The distal centriole gives rise to a flagellum that grows at the same pace as the cortical microtubules. Migration of the nucleus takes place after the formation of the flagellum. It is followed by the separation of the old spermatid from the residual cytoplasm. The mature H. nana spermatozoon is filiform and lacks mitochondria. The axoneme, of the 9 + "1" pattern of the Platyhelminthes, does not reach the extremities of the spermatozoon. The nucleus is electron dense and is in close contact with the axoneme around which it coils in a spiral making an angle of 10 degrees to 15 degrees with the spermatozoon axis. The cortical microtubules follow a 10 degrees to 15 degrees helicoidal path along almost their whole length, except at their posterior extremity, where they are parallel to the spermatozoon axis. H. nana is distinguished by the early development of 12 crested-like bodies of different lengths and by the existence of a single centriole in the differentiation zone. Such a high number of crested-like bodies had never previously been reported in a cestode.     

Spermiogenesis and structure of spermatozoa in the oribatid mite,Hafenrefferia gilvipes (C.L. Koch) (Acari,Oribatida)

The process of spermiogenesis and the structure of spermatozoa in the mite, Hafenrefferia gilvipes (Koch) were studied ultrastructurally. Spermiogenesis was divided into six stages. The spermatids at stage 1 have the usual structure. At stage 2 the structure of the mitochondria and their distribution in the spermatid start to change, leading to the formation of specific mitochondrial derivatives which are subsequently incorporated into the nucleus of the spermatozoon. Parallel to the transformation of mitochondria occurs a reorganization of the nuclear material. The fully formed spermatozoon has a tadpole-like shape, with the cell nucleus located in the distended part of the cell, and containing mitochondrial derivatives in its karyoplasm. Acrosome, flagellum and centrioles are absent. The participation of peripherally distributed microtubules, present in spermatids at stages 4 to 6, in the shaping of the spermatozoon has been suggested.     

Spermatological characters of monozoic tapeworms (Cestoda: Caryophyllidea), including first data on a species from the Indomalayan catfish

The ultrastructure of spermiogenesis and mature spermatozoon in Lytocestus indicus (Cestoda: Lytocestidae) is described; this is the first representative of this group of monozoic, presumably most basal, tapeworms (Eucestoda) from the Indomalayan region to be documented in this manner. Similarly, as in other caryophyllideans, its spermiogenesis involves the formation of a conical differentiation zone with 2 centrioles associated with striated roots and an intercentriolar body. In the course of the process, 1 of the centrioles develops a free flagellum, which fuses with a cytoplasmic protrusion, whereas the other remains oriented in a cytoplasmic bud. Spermiogenesis is also characterized by the presence of electron-dense material in the early stages of spermiogenesis and a slight rotation of the flagellar bud. The mature spermatozoon of L. indicus is a filiform cell tapered at both extremities that lacks mitochondria; its nucleus has parallel disposition to the axoneme and does not reach up to the posterior extremity of the spermatozoon, which is typical for spermatozoa of the type III pattern. The new data confirm that caryophyllideans share the same type of spermiogenesis that is considered to be plesiomorphic in the Eucestoda. The existing information on spermatological ultrastructure of 8 members for 3 of 4 caryophyllidean families from different host groups (cyprinids and catostomids, both Cypriniformes, and mochokids and clariids, both Siluriformes) from 4 zoogeographical regions (Palearctic, Neotropic, Ethiopian, and Indomalayan regions) demonstrates great uniformity in spermiogenesis and sperm ultrastructure, which does not reflect different taxonomic position of the species studied.     

Ultrastructure of spermiogenesis and the spermatozoon of Mesocestoides litteratus (Cestoda, Mesocestoididae).

This paper constitutes the first ultrastructural study of spermiogenesis and the spermatozoon of a cestode belonging to the family Mesocestoididae, Mesocestoides litteratus. Spermiogenesis in M. litteratus is characterised by a flagellar rotation and a proximodistal fusion. The zone of differentiation presents striated roots associated with the centrioles and also an intercentriolar body. The most interesting ultrastructural feature found in the mature spermatozoon of M. litteratus is the presence of parallel cortical microtubules. The spermatozoon also exhibits a single crest-like body and granules of glycogen. The pattern of spermiogenesis and the parallel position of cortical microtubules reveal the lack of concordance between M. litteratus and cyclophyllidean species studied to date in spermiogenesis and in the ultrastructural organisation of spermatozoon. This study provides new spermatological data and calls into question the validity of the current systematic position of mesocestoidids.     

Spermiogenesis and fine structure of the spermatozoon in a headstander, Chilodus punctatus (Teleostei, Characiformes, Anostomidae)

The main characteristic features of spermiogenesis in Chilodus punctatus (Characiformes) are rotation of the nucleus, development of a nuclear fossa, which extends as a narrow invagination deep into the nucleus and the way in which flagellum is formed. The chromatin condensation proceeds during the spermiogenesis from heterogeneous through homogenous and granular to a highly compact one present in the mature spermatozoon. Mature Ch. punctatus spermatozoon shows a spherical nucleus, short midpiece and flagellum with lateral fins. The centrioles are in perpendicular arrangement and are located in the deep nuclear fossa, which extends towards the anterior pole of the nucleus. The midpiece contains a few mitochondria, which are separated from the anterior fragment of flagellum by the cytoplasmic channel. Spermiogenesis and spermatozoon ultrastructure conform to the pattern observed in other ostariophysans, but for the first time the presence of lateral fins along flagellum has been documented in a representative of Characiformes.     

Ultrastructural study of spermiogenesis and the spermatozoon of Microcotyle pancerii (Monogenea: Polyopisthocotylea: Microcotylidae), parasite of meagre Argyrosomus regius (Pisces: Teleostei)

The present work deals with the ultrastructure of spermiogenesis and the spermatozoon of Microcotyle pancerii, a gill parasite of meagre Argyrosomus regius collected in Corsican fish farms. Spermiogenesis was rather similar to that observed in other polyopisthocotylean Monogenea. The intercentriolar body was different from that described in digeneans. The nuclear condensation occurred in 2 successive stages. First, during the nuclear migration in the median cytoplasmic process, the nucleus developed a honeycomb-like appearance. Then, after the flagellar fusion, a discontinuous twisting of the chromatin appeared along the nucleus, with this process ending in total nuclear condensation. The structure of the spermatozoon is characterized by 2 axonemes (9 + "1" pattern), a single and continuous field of cortical microtubules, a mitochondrion, and a nucleus. Our findings were compared with various ultrastructural features in order to highlight variability within the group.     

Spermiogenesis and spermatozoon ultrastructure of the cranial digenean Troglotrema acutum (Leuckart, 1842)

Ultrastructure of spermiogenesis and the main characters of the mature spermatozoon of Troglotrema acutum are described by means of transmission electron microscopy. Specimens were obtained from the nasolacrimal sinuses of an American mink (Mustela vison). Spermiogenesis in T. acutum follows the general pattern of digeneans. The zone of differentiation is a conical-shaped area bordered by cortical microtubules and delimited at its base by a ring of arched membranes. This area contains 2 centrioles associated with striated rootlets and an intercentriolar body between them. The centrioles develop 2 free flagella that grow ortogonally to the median cytoplasmic process. The posterior flagellar rotation and proximodistal fusion of the free flagella with the median cytoplasmic process originate the spermatozoon. The mature spermatozoon of T. acutum is characterized by the presence of 2 axonemes of different lengths presenting the 9+'1' trepaxonematan pattern, 2 bundles of parallel cortical microtubules, 2 mitochondria, a nucleus, and granules of glycogen. These ultrastructural characters are compared with other digenean species previously studied and the importance of different spermatological features is discussed.     

Ultrastructure of spermiogenesis and spermatozoa of Gymnotus cf. anguillaris and Brachyhypopomus cf. pinnicaudatus (Teleostei: Gymnotiformes)

The ultrastructure of spermiogenic stages and spermatozoa of representatives of two gymnotiform families, Gymnotus cf. anguillaris (Gymnotidae) and Brachyhypopomus cf. pinnicaudatus (Hypopomidae) were studied. Spermiogenesis of both species is characterized by lateral development of the flagellum and formation of a nuclear fossa. Some differences were found between these species, such as whether (B. cf. pinnicaudatus) or not (G. cf. anguillaris) nuclear rotation occurs, permanence of the cytoplasmic channel, and type and localization of the nuclear fossa. In the G. cf. anguillaris spermatozoon the nucleus is spherical with highly condensed chromatin. The nuclear fossa is shallow and lateral and is associated with the centriolar complex through stabilizing fibrils. The midpiece is short, with many vesicles, a cytoplasmic channel, and elongate mitochondria. In the B. cf. pinnicaudatus spermatozoon the ovoid nucleus is elongated lateral and posterior to the centriolar complex, and has highly condensed chromatin. The eccentric nuclear fossa is of the moderate type, and contains the entire centriolar complex. The midpiece is long, with numerous vesicles, elongate mitochondria, and no cytoplasmic channel. In both species the flagella are laterally disposed in relation to the nucleus and comprise of the classical 9+2 axoneme. Most of the characteristics found in the spermatozoa of these two species of Gymnotiformes are shared with species of Characiformes, whereas only a few are also found in Siluriformes. This suggests that Gymnotiformes and Characiformes may be more closely related than previously proposed.     

Sperm characters of the digenean Nephrotrema truncatum (Troglotrematidae): a kidney parasite of Crocidura russula (Soricidae) and their phylogenetic significance

ABSTRACT

Spermatological characteristics of the troglotrematid digenean Nephrotrema truncatum, a parasite of the shrew Crocidura russula, have been investigated by means of transmission electron microscopy. The ultrastructural study reveals that the mature spermatozoon of N. truncatum exhibits many ultrastructural characters previously described in most gorgoderoideans. These are two axonemes of the 9+‘1‘ trepaxonematan pattern, four attachment zones, a lateral expansion, an external ornamentation of the plasma membrane associated with spine-like bodies and cortical microtubules, and in the posterior part of the anterior spermatozoon region, two bundles of parallel cortical microtubules with the maximum number located in the anterior part of the spermatozoon, a nucleus, two mitochondria, and granules of glycogen. The obtained results are compared with those of other digeneans, particularly the Gorgoderoidea. The sperm cells gorgoderoideans are of type IV, characterised by a 9+‘1‘ pattern of axonemes, the presence of an external ornamentation associated with cortical microtubules and located in the posterior area of the anterior extremity, the presence of two bundles of cortical microtubules, the maximum number of cortical microtubules located in the anterior region of the spermatozoon, and the presence of generally two mitochondria. However, dicrocoeliids and troglotrematids have spermatozoa with ornamentation of the plasma membrane and lateral expansions.     

Spermiogenesis and spermatozoon ultrastructure of the dilepidid cestode Molluscotaenia crassiscolex (von Linstow, 1890), an intestinal parasite of the common shrew Sorex araneus

Marigo, A.M., Bâ, C.T. and Miquel, J. 2011. Spermiogenesis and spermatozoon ultrastructure of the dilepidid cestode Molluscotaenia crassiscolex (von Linstow, 1890), an intestinal parasite of the common shrew Sorex araneus. —Acta Zoologica (Stockholm) 92 : 116–125. Spermiogenesis in Molluscotaenia crassiscolex begins with the formation of a differentiation zone containing two centrioles. One of the centrioles develops a flagellum directly into the cytoplasmic extension. The nucleus elongates and later migrates along the spermatid body. During advanced stages of spermiogenesis, a periaxonemal sheath appears in the spermatid. Spermiogenesis finishes with the appearance of a single helicoidal crested body at the base of the spermatid and, finally, the narrowing of the ring of arched membranes causes the detachment of the fully formed spermatozoon. The mature spermatozoon of M. crassiscolex exhibits a partially detached crested body in the anterior region of the spermatozoon, one axoneme, twisted cortical microtubules, a periaxonemal sheath, and a spiralled nucleus. The anterior spermatozoon extremity is characterized by the presence of an electron‐dense apical cone and a single spiralled crested body, which is attached to the sperm cell in the anterior and posterior areas of region I, whereas in the middle area it is partially detached from the cell. This crested body is described for the first time in cestodes. The posterior extremity of the male gamete exhibits only the disorganizing axoneme. Results are discussed and compared particularly with the available ultrastructural data on dilepidids sensu lato.