Ultrastructure of the spermatozoon of Centroderma spinosissima (Stossich, 1886) (Digenea: Mesometridae) and its phylogenetic potential

The Mesometridae includes only five genera and eight species. The available data on the ultrastructure of sperm cells of mesometrid species referred to two species only, Elstia stossichianum and Wardula capitellata. The present study revealed the ultrastructure of the spermatozoon of a third genus and third species of Mesometridae, Centroderma spinosissima. The mature spermatozoon of C. spinosissima presents two axonemes with different lengths of the Ehlers’ 9 + ‘1’ trepaxonematan pattern, a nucleus, two mitochondria, two bundles of parallel cortical microtubules, external ornamentation of the plasma membrane, a lateral expansion, spine-like bodies, cytoplasmic ornamented buttons and granules of glycogen. The spermatozoon of C. spinosissima is similar to those of the previously studied mesometrids. However, some peculiarities such as the presence of two mitochondria, the disposition of the external ornamentation of the plasma membrane and the morphology of the posterior spermatozoon extremity, characterize the male gamete of C. spinosissima. Moreover, the presence of cytoplasmic ornamented buttons is a characteristic found only in the mature spermatozoon of mesometrids and it probably represents an autapomorphy for this family.     

Sperm ultrastructure of the digenean Aphallus tubarium (Rudolphi, 1819) Poche, 1926 (Platyhelminthes, Cryptogonimidae) intestinal parasite of Dentex dentex (Pisces, Teleostei)

The ultrastructural organization of the spermatozoon of a cryptogonimid digenean, Aphallus tubarium, a parasite of Dentex dentex, is described. The spermatozoon possesses the elements found in other digeneans: two axonemes with 9 + “1” pattern, a mitochondrion, a nucleus, cortical microtubules, external ornamentation and spine-like bodies. However, the mitochondrion appears as a cord with a bulge; this characteristic has never been described in other studied cryptogonimid and in other digeneans except in one lepocreadiid, Holorchis micracanthum. Likewise, the presence of a thin cytoplasm termination in the anterior part of the spermatozoon has never been pointed out in the cryptogonimids.     

Ultrastructure of the spermatozoon of the digenean Cricocephalus albus (Kuhl & van Hasselt, 1822) Looss, 1899 (Platyhelminthes, Pronocephaloidea, Pronocephalidae), parasite of “the hawksbill sea turtle” Eretmochelys imbricata (Linnaeus, 1766) in Senegal

The mature spermatozoon of Cricocephalus albus is filiform, tapered at both ends and shows the following features: 2 axonemes of different lengths presenting the 9 + “1” trepaxonematan pattern, 2 bundles of parallel cortical microtubules, a mitochondrion and a nucleus. Nevertheless, the particularity of the spermatozoon of C. albus is its anterior extremity with an apical electron-dense material associated with extramembranar ornamentation, a cytoplasmic dorsolateral expansion and spine-like bodies. To our knowledge, such an anterior extremity of the spermatozoon has not previously been described from a species of the superfamily Pronocephaloidea. Our study provides new data on the mature gamete of C. albus in order to improve our understanding of the pronocephaloidean phylogenetic relationships.     

Ultrastructure of the spermatozoon of the digenean Plagiorchis elegans (Rudolphi, 1802) (Plagiorchioidea,Plagiorchiidae)

The ultrastructure of the mature spermatozoon of the type genus of the Plagiorchiidae Plagiorchis elegans (Rudolphi, 1802), a parasite of the Golden hamster, Mesocricetus auratus is described. This study is the first ultrastructural study of the spermatozoon of a Plagiorchis, the second of a plagiorchiid species and only the third in the Plagiorchioidea. Previously data on spermatozoon ultrastructure existed only for the plagiorchiid Enodiotrema reductum and the omphalometrid Rubenstrema exasperatum. The mature spermatozoon of P. elegans exhibited the general pattern described in most digenean species, namely two axonemes of the 9 + “1” Trepaxonemata pattern, nucleus, mitochondria, external ornamentation of the plasma membrane, spine‐like bodies, and glycogen granules. However, the rather typical expansion of the plasma membrane is not found in P. elegans. Another peculiarity of the spermatozoon of P. elegans is the presence of a structure called thin cytoplasm termination. Spermatozoon ultrastructure of P. elegans is compared with that of E. reductum and R. exasperatum. Spermatozoon of P. elegans conforms to the general pattern described in E. reductum. Thus, this study further expands our knowledge on the spermatozoon ultrastructure among the members of the Plagiorchioidea, one of the most phylogenetically derived groups of the digenea. J. Morphol. 274:965–972, 2013. © 2013 Wiley Periodicals, Inc.     

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.     

Ultrastructural study of the male gamete of Pleurogonius truncatus Prudhoe, 1944 (Platyhelminthes, Digenea, Pronocephalidae) parasite of Eretmochelys imbricata (Linnaeus, 1766)

In Pronocephaloidea, the spermatozoa of only two species have been studied today. Because of this, we present in this work data concerning to a third specie, Pleurogonius truncatus Prudhoe, 1944. The mature spermatozoon of P. truncatus possesses two axonemes with the 9+"1" pattern typical of Trepaxonemata, mitochondrion, nucleus, parallel cortical microtubules, spinelike bodies, cytoplasmic expansion and an external ornamentation of the plasma membrane. A particularity of the spermatozoon of P. truncatus is in the ultrastructure of the anterior spermatozoon extremity with only cortical microtubules and ornamentation of the plasma membrane. This type of anterior extremity has never been described until today in Pronocephaloidea. On the other hand, the ultrastructure of the posterior extremity of the spermatozoon confirms that already described in Pronocephalidae.     

The ultrastructural characters of the mature spermatozoon of Opechona bacillaris (Molin, 1859) (Digenea,Lepocreadiidae) a parasite of Scomber colias Gmelin, 1789 (Scombridae) off the coast of Dakar (Senegal)

This study presents the ultrastructure of the mature spermatozoon of Opechona bacillaris, a digenean belonging to the family Lepocreadiidae. The sperm cell of O. bacillaris exhibits the general pattern described in most of the Lepocreadioidea: two axonemes of the 9 + ‘1’ pattern of the Trepaxonemata, mitochondria, a cortical mitochondrion, a nucleus, electron‐dense material in the anterior extremity of the spermatozoon, external ornamentation of the plasma membrane with associated spinelike bodies, and granules of glycogen. However, particularities of O. bacillaris are the simultaneous presence in the anterior extremity of the spermatozoon of the electron‐dense material, a mitochondrion, and the absence of cortical microtubules. In the Lepocreadiidae, we describe for the first time in O. bacillaris spinelike bodies associated with the external ornamentation of the plasma membrane and two mitochondria. The first mitochondrion is moniliform and composed of a mitochondrial cord with joined mitochondrial bulges. The second mitochondrion shows a regular form. The posterior tip of the spermatozoon has only singlets to owing to the disorganization of the second axoneme and granules of glycogen as occurs in Hypocreadium caputvadum, the other studied species of the family Lepocreadiidae.     

Ultrastructural study of vitellogenesis and oogenesis of Metadena depressa (Stossich, 1883) Linton, 1910 (Digenea,Cryptogonimidae), intestinal parasite of Dentex dentex (Pisces,Teleostei)

The ultrastructural organization of the female reproductive system of Metadena depressa, digenean intestinal parasite of Sparidae (Dentex dentex), was investigated by electron microscopy. The vitellogenesis is divided into four stages: stage I, vitellocytes have a cytoplasm mainly filled with ribosomes and few mitochondria; stage II, beginning of the synthetic activity; stage III, active shell globule clusters synthesis; stage IV, mature vitellocytes are filled with shell globule clusters and generally contain several large lipid droplets. Glycogen granules are grouped at the periphery of the cell. The three stages of the oogenesis process take place in the ovary: stage I, oogonia are undifferentiated small cells located at the periphery of the organ; stage II, primary oocytes possess a higher nucleo-cytoplasmic ratio and a nucleus with a nucleolus and synaptonemal complexes indicating the zygotene-pachytene stage of the first meiotic division; stage III, mature oocytes are located in the proximal region of the organ and possess a cytoplasmic chromatoid body and cortical granules in a monolayer close to the periphery of the cell.     

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.     

Ultrastructural description of the life cycle of Nosema monorchis n. sp. (Microspora, Nosematidae), hyperparasite of Monorchis parvus (Digenea, Monorchiidae), intestinal parasite of Diplodus annularis (Pisces, Teleostei)

Life cycle stages of a new species of the genus Nosema Naegeli, 1857 (Microspora, Nosematidae), were examined by light and electron microscopy. It parasitizes the gut and the uterus of the digenean Monorchis parvus (Monorchiidae), in Diplodus annularis (Pisces, Teleostei). All stages were in close contact with the cytoplasm of the host cell and were probably all diplokaryotic. The divisions of meronts and sporonts were recognizable by the formation of spindle plaques at the surface of the nucleus. Spores were oval, measured 3.2±0.3×2.5±0.2 μm on ultrathin sections, and had a polar filament with 16–17 coils. The polaroplast presented two parts: an anterior region with closely packed lamellae and a posterior part with wider lamellae. This Nosema species is compared with the other microsporidian parasites of digeneans. This new species is named Nosema monorchis n. sp., after the generic name of its host.     

Ultrastructural study of the spermatozoon of Heterolebes maculosus (Digenea,Opistholebetidae), a parasite of the porcupinefish Diodon hystrix (Pisces,Teleostei)

This paper describes the ultrastructure of the mature spermatozoon of Heterolebes maculosus. It is the first study of this kind concerning the Opistholebetidae (Platyhelminthes, Digenea). The ultrastructural elements observed in the spermatozoon are: two axonemes with 9+“1” pattern of Trepaxonemata and their attachment zones, two mitochondria, a nucleus, cortical microtubules, external ornamentation of the plasma membrane and spine-like bodies. The number and the disposition of cortical microtubules, the organisation of 11 cortical microtubules disposed in semi-circle around the first mitochondrion in the external ornamentation region and the organisation of the posterior part of the spermatozoon are discussed. Three principal types of posterior part of digenean spermatozoa are proposed. The similarity between the spermatozoon of the Opistholebetidae H. maculosus and Opecoelidae enables us to confirm that these two families are closely related.     

Ultrastructure of the spermatozoon of Anomotaenia quelea (Mettrick, 1961) (Cestoda,Cyclophyllidea, Dilepididae), an intestinal parasite of Quelea quelea (Aves,Ploceidae) in Senegal

The mature spermatozoon of Anomotaenia quelea exhibits an apical cone of electron-dense material and two helicoidal crest-like bodies. The apical cone near its base is surrounded by a lucent cytoplasm and a spiraled layer of cortical microtubules. The crest-like bodies are of different lengths, spiraled and make an angle of 30–40° to the hypothetical spermatozoon axis. The axoneme is of the 9 + ‘1’ trepaxonematan pattern and is surrounded by a periaxonemal sheath of electron-dense material. The cytoplasm contains in regions III and IV numerous electron-dense granules situated between the periaxonemal sheath and the cortical microtubules. The posterior extremity of the spermatozoon of A. quelea exhibits a nucleus and a disorganized axoneme and cortical microtubules. This type of posterior extremity of the mature spermatozoon has never been described previously in a Dilepididae. Similarly, two crest-like bodies have not been observed before in a dilepidid cestode.     

Ultrastructural characters of the spermatozoon of the digenean Hypocreadium caputvadum Kacem et al., 2011 (Lepocreadioidea: Lepocreadiidae), an intestinal parasite of Balistes capriscus in Tunisia

The ultrastructural organization of the spermatozoon of the digenean Hypocreadium caputvadum (Lepocreadioidea: Lepocreadiidae) is described. Live digeneans were collected from Balistes capriscus (Teleostei: Balistidae) from the Gulf of Gabès, Tunisia (Eastern Mediterranean Sea). The mature spermatozoon of H. caputvadum shows several ultrastructural characters such as two axonemes of different lengths exhibiting the classical 9 + “1” trepaxonematan pattern, a nucleus, two mitochondria, granules of glycogen, external ornamentation of the plasma membrane and two bundles of parallel cortical microtubules. Moreover, in the anterior extremity, the second axoneme is partly surrounded by a discontinuous and submembranous layer of electron-dense material. Our study provides new data on the spermatozoon of H. caputvadum in order to improve the understanding of phylogenetic relationships in the Digenea, particularly in the superfamily Lepocreadioidea. In this context, the electron-dense material surrounding one of the axonemes in the anterior spermatozoon extremity constitutes the unique distinguishing ultrastructural character of lepocreadioideans, and it is present in spermatozoa of lepocreadiids, aephnidiogenids and gyliauchenids.     

Ultrastructure of the spermatozoon of Anomotaenia quelea (Mettrick, 1961) (Cestoda,Cyclophyllidea, Dilepididae), an intestinal parasite of Quelea quelea (Aves,Ploceidae) in Senegal

The mature spermatozoon of Anomotaenia quelea exhibits an apical cone of electron-dense material and two helicoidal crest-like bodies. The apical cone near its base is surrounded by a lucent cytoplasm and a spiraled layer of cortical microtubules. The crest-like bodies are of different lengths, spiraled and make an angle of 30–40° to the hypothetical spermatozoon axis. The axoneme is of the 9 + ‘1’ trepaxonematan pattern and is surrounded by a periaxonemal sheath of electron-dense material. The cytoplasm contains in regions III and IV numerous electron-dense granules situated between the periaxonemal sheath and the cortical microtubules. The posterior extremity of the spermatozoon of A. quelea exhibits a nucleus and a disorganized axoneme and cortical microtubules. This type of posterior extremity of the mature spermatozoon has never been described previously in a Dilepididae. Similarly, two crest-like bodies have not been observed before in a dilepidid cestode.     

The spermatozoon of Mengenilla moldrzyki (Strepsiptera,Mengenillidae): Ultrastructure and phylogenetic considerations

Even though the spermatozoa of several strepsipteran species were described earlier, no data were available for the basal family Mengenillidae. Well-fixed material of the recently described Tunisian species Mengenilla moldrzyki was used for a detailed examination of the sperm ultrastructure. The total length is c. 30 μm. The head region contains a conical acrosome vesicle (0.3-0.35 μm) and an elongated nucleus (7.3 μm) with dense chromatin. Some granular material along with a uniformely dense centriole adjunct and two mitochondrial derivatives are visible at the posterior end of the nucleus. The material of the centriole adjunct does not extend along the flagellum and accessory bodies are absent. The mitochondrial derivatives are elongated structures crossed by a longitudinal crista but lacking parallel transverse cristae and paracrystalline material in the dense matrix. The mitochondrial derivatives gradually reduce their size and end at the most posterior tail region. The flagellar axoneme has a 9 + 9 + 2 pattern and originates beneath the nucleus. In the terminal tail region the axoneme gradually disintegrates. Despite the extreme specialization of the endoparasitc group, strepsipteran spermatozoa are mostly characterized by plesiomorphies. The pattern within the order is largely uniform, but Mengenilla displays several apomorphic features compared to the presumptive strepsipteran groundplan (e.g., absence of crystallizations and cristae in the mitochondrial derivatives). The subdivision of the intertubular material into two compartments with a dense beak-like structure adhering to the tubular wall supports a clade Coleopterida (=Strepsiptera + Coleoptera) + Neuropterida.     

Ultrastructural study of spermiogenesis and the spermatozoon of Crepidostomum metoecus (Digenea: Allocreadiidae), a parasite of Salmo trutta (Pisces: Teleostei)

Spermiogenesis and the spermatozoon of Crepidostomum metoecus, an intestinal parasite of brown trout Salmo trutta, were studied by transmission electron microscopy. Spermiogenesis begins with the formation of a differentiation zone in front of 2 centrioles associated by an intercentriolar body. Each centriole is linked to a striated rootlet, and gives rise to a flagellum. The rotation of flagella is greater than 90 degrees; their fusion with the median cytoplasmic extension is proximodistal and asynchronous. The spermatozoon is formed after constriction of arched membranes. The spermatozoon possesses 2 axonemes of the 9 + "1" pattern, a nucleus, mitochondria, and glycogen. A major feature is the presence, in the anterior part, of external ornamentation and a lateral expansion associated with spinelike bodies. Another attribute is the presence of 2 mitochondria rather than just 1, as in most of the digenean spermatozoa. To our knowledge, this study is the first undertaken with a species of the Allocreadiidae.     

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.     

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.