Ultrastructure of the spermatozoon of <Emphasis Type="Italic">Talpa romana</Emphasis> (Mammalia,Lipotyphla)

In this study, we used SEM and TEM to investigate the ultrastructure of spermatozoa from the cauda epididymis of Talpa romana. For comparison, we also analysed spermatozoa from the cauda epididymis of T. europaea captured in the same area. The male gamete of T. romana has a flattened head with an elliptic profile, consisting of a large acrosome and a nuclear region separated by a thin subacrosomal space. At the tip of the nucleus, the subacrosomal space ends in a finger-shaped projection. The tail includes a connecting piece, middle piece, principal piece and end piece. The male gametes of T. romana are substantially similar to those of T. europaea. A comparison with other species of insectivores permits extension of the similarity of sperm features to Scalopus aquaticus and Condylura cristata. Many spermatozoa from the cauda epididymis of T. romana and T. europaea have the tail bent at the annulus, and this is always associated with remnants of cytoplasmic droplets. This morphology is considered to be a common phenomenon.     

Ultrastructure of spermiogenesis and spermatozoa in Bradynectes sterreri and remarks on sperm cells in Haplopharynx rostratus and Paromalostomum fusculum: phylogenetic implications for the Macrostomorpha (Plathelminthes)

 The fine structure of spermiogenesis and spermatozoa in three species of the Macrostomorpha was studied, with emphasis on Bradynectes sterreri. Two centrioles appear during the development of sperm cells, at least in B. sterreri and Paromalostomum fusculum. Initially these organelles have a perpendicular position, but later they come to lie in line with each other. In P. fusculum, the differentiation of rootlet structures inserting on both centrioles was found. However, ciliary axonemes do not grow out, either in B. sterreri or in P. fusculum. These two species, and also Haplopharynx rostratus, have aciliated spermatozoa. The mature male gametes of B. sterreri are characterized by a filiform nucleus, numerous mitochondria, dense bodies irregular in shape, membranous lacunae, a pair of electron-dense lateral ledges and two sets of cortical microtubules in addition to a closed ring of microtubules in the posterior segment of the cell. Both lateral ledges do not originate from the centrioles. ’Lateral ledges’ or ’lateral bristles’ were not observed in spermatozoa of H. rostratus and P. fusculum. Such structures cannot be considered autapomorphic for the Macrostomorpha. The known spermatological characteristics contribute to elucidating the interrelationships of the Macrostomorpha. Haplopharynx and Macrostomida are sister groups. Spermatozoa with cortical microtubules separated into two sets are hypothesized as an autapomorphy of the Macrostomida. The two lateral ledges found in spermatozoa of B. sterreri are discussed to correspond to the pair of ’lateral bristles’ known from Macrostomum species, indicating a sister-group relationship of these two taxa. Apparently, the aciliated spermatozoa of Macrostomorpha species originated from biciliated male gametes. Hence, biciliated spermatozoa are not an evolutionary novelty of the Trepaxonemata, but of the Rhabditophora. Accepted: 22 February 1999     

Morphology of the spermatozoon in two sympatric species of Fissurella Bruguière, 1789 (Mollusca: Vetigastropoda) from Southern Chile

Summary

Light and electron microscopy were used to analyze the morphology and ultrastructure of the spermatozoon of Fissurella nigra and Fissurella picta, two sympatric species of keyhole limpets from the southern Chilean coast. The spermatozoa of both species are of the aquasperm type, typical of species with external fertilization. Each species had its own distinctive spermatic morphology, particularly in relation to size. Proceeding from anterior to posterior, the spermatozoa of both species each consists of an elongated head with a conical acrosome having a deep subacrosomal space and truncated conical nucleus, followed by a midpiece containing five mitochondria associated in a compact ring around the proximal and distal centrioles, and, at the end, a flagellum. The spermatozoon head of F. nigra is almost twice as long as that of F. picta. This difference constitutes the first morphological evidence that the size of the spermatozoon could represent a candidate for the maintenance of reproductive isolation between these two sympatric species.     

The ultrastructure of the spermatozoon of the hoplonemertine,Emplectonema neesii

Summary Mature spermatozoa of the hoplonemertine, Emplectonema neesii were studied by light and electron microscopy. The spermatozoa are flagellate and motile, each gamete consisting of an elongate anterior head and a posterior flagellar tail. Three regions are identifiable in the head, the acrosome, a nuclear zone and a connecting piece containing two centrioles. The nuclear zone contains glycogen granules as well as an elongate, grooved nucleus and a large mitochondrion whose lobes interdigitate with the nuclear grooves. The flagellum has a typical 9 + 2 flagellar tubule organisation. Nemertine spermatozoan ultrastructure, as exemplified by that of E. neesii, is compared with that of platyhelminth male gametes and the supposed phylogenetic affinity of the two taxeis reexamined in the light of the results of this comparison.My thanks are due to Miss A. Harding and Miss J. Webb for collecting sexually mature E. neesii, and to Dr. R. G. Crump for laboratory facilities at the Orielton Field Centre, Pembrokeshire, Wales. The work was carried out during the tenure of a research grant from The Nuffield Foundation.     

Spermatogenesis and the structure of the testes in Nemertodermatida

The ultrastructure of the testes in two representatives of the enigmatic taxon Nemertodermatida was studied using transmission electron microscopy. Nemertoderma westbladi has paired testes, which are delineated by lining cells. Within each testis, different follicles, each surrounded by a membrane-like structure, are found. Flagellophora apelti has genuinely follicular testes, consisting of several follicles, each containing a certain stage of spermatogenesis. As the gametes are not enclosed by a structure that can be called a true gonad, the structure of the testes differs from most bilaterian animals, but resembles the organization of gametogenic areas of ctenophores. Each stage of spermatogenesis in F. apelti is described, enabling the inference of the origin of the structures seen in mature spermatozoa. The overall structure of the mature spermatozoa is similar in all nemertodermatids and unique within the Metazoa: an elongated head containing the nucleus; a middle piece containing an axoneme, mitochondrial derivatives and in F. apelti granular derivatives; and a flagellar tail.     

Fine structure of spermatozoa inAnthopharynx sacculipenis (Plathelminthes,Solenopharyngidae)

Summary The organisation of the spermatozoa ofAnthopharynx sacculipenis is described, based on electron-microscopical observations. The male gametes are fili-form in shape. They are totally enclosed by cortical microtubules and possess two free cilia. Special features are dot-like dense granules arranged in regular rows and terraced elaborations of the nuclear membrane. Such terraced elaborations are not known in any other species of flatworms whereas dot-like dense granules are described for some other taxa of the Rhabdocoela. Male gametes do not show synapomorphic correspondences between the Solenopharyngidae and the Prolecithiphora.Abbreviations ci cilia - ct cortical microtubules - db dense bodies - gl glycogen - mi mitochondrion - n nucleus - nt nuclear terraces     

Interspecific Variation in Structural Organisation of the Spermatozoon in the Asian Bandicoot Rats,Bandicota Species (family Muridae)

The structural organisation of the spermatozoon from two species of bandicoot rats Bandicota bengalensis and Bandicota indica was investigated by light and electron microscopy together with the effect of incubation in Triton-X 100 and sodium dodecyl sulphate. The sperm head of B. bengalensis is invariably falciform, has a uniform electron-dense nucleus capped by an acrosome with a posteriolateral equatorial segment, a subacrosomal cytoskeleton with a large rostral perforatorium, and a sperm tail, attached to the lower concave surface of the sperm head, with typical coarse fibres and fibrous sheath. By contrast, the sperm head shapes of B. indica are generally conical or bulbous, the nucleus contains a few large vacuoles, the acrosome lacks an equatorial segment, no recognisable perforatorium occurs, and the sperm tail, which is attached basally, is very short with only modest development of coarse fibres and fibrous sheath. These results indicate that, within the genus Bandicota, huge interspecific differences in morphology of the spermatozoon have evolved. The spermatozoa of B. bengalensis are similar to those of Rattus and many other murids and thus presumably represent the ancestral condition, whereas those of B. indica (and B. savilei) are unlike spermatozoa from any other eutherian mammal so far described. © 1998 The Royal Swedish Academy of Sciences. Published by Elsevier Science Ltd. All rights reserved     

Structure and ultrastructure of spermatozoa and spermiogenesis in three species of Lucilia Robineau‐desvoidy, 1830 (Diptera: Calliphoridae)

Morphology of male internal reproductive organs, spermatozoa, and spermiogenesis of the blow‐flies Lucilia cuprina, Lucilia eximia, and Lucilia peruviana is first described here, using light and transmission electron microscopy. Spermiogenesis follows the characteristics described for others insect species. The spermatozoa of L. cuprina are similar to those described for other Brachycera. However, in L. eximia and L. peruviana, some differences were found. In L. cuprina and L. eximia species, the spermatozoa are long and thin, measuring about 211 μm and 146 μm in length, of which the head region measures approximately 19 μm and 17 μm, respectively. A polymorphism was observed in L. cuprina and L. eximia spermatozoa. In all three species, the head includes a monolayered acrosome with electron‐lucent material. The shape of the nucleus, in cross sections, varies from circular to oval with completely condensed chromatin. Implantation of the axoneme was observed in the middle region of the nucleus, known as the “peg” region. In the next region, the beginning of two mitochondrial derivatives of similar diameter and different lengths in L. cuprina and only one in L. eximia and L. peruviana was observed. In the overlap region, the following structures were observed: nucleus, centriolar adjunct, mitochondrial derivatives, and axoneme. The axoneme is of a conventional insectan type with a 9 + 9 + 2 microtubular arrangement. The male internal reproductive tract consists of testis, deferent ducts, a strongly developed seminal vesicle, accessory glands, and ejaculatory duct. These features are consistent with the structural diversity of the dipteran reproductive tract and spermatozoa, comprising an essential tool for understanding the complex variations found in the Diptera. J. Morphol. 2011. © 2011 Wiley Periodicals, Inc.     

A comparison of the structure of the spermatozoa and spermatogenesis of 16 species of patellid limpet (Mollusca: Gastropoda: Archaeogastropoda)

Light and transmission electron microscopy of the spermatozoa and spermatogenesis of 16 species (in three genera, Patella, Helcion, Cellana) of patellid limpet have shown that head lengths of the sperm range from 3 to 13 μm, and each species has a sperm with a unique morphology, indicating that the spermatozoa can be used as a taxonomic character. Although spermatozoon structure is species specific, five types can be recognized, based on the size, shape, and structure of the nucleus and acrosome. The occurrence of five morphological types of sperm, one of which (Cellana capensis) is particularly different from other patellids, suggests that the taxonomy of the family Patellidae be re-examined. The morphological changes that occur during spermatogenesis are very similar in all species, although two patterns of chromatin condensation are found. Those species with sperm that have short squat nuclei (length:breadth < 3.5:1) have a granular pattern of condensation. Species with sperm that have more elongate nuclei (length:breadth > 5:1) have an initial granular phase followed by the formation of chromatin fibrils. These fibrils become organized along the long axis of the elongating nucleus. The absence of a manchette suggests that nuclear elongation is brought about from within the nucleus.     

Spermiogenesis and spermatozoa ultrastructure of Aonides oxycephala (Annelida: Spionidae) from the Sea of Japan

Adults of Aonides oxycephala, common inhabitants of shallow boreal waters in the Atlantic and Pacific Oceans, release gametes into the water where fertilization and lecithotrophic larval development occur. During spermiogenesis, the acrosomal vesicle migrates from the posterior to the anterior end of the spermatid and the number of mitochondria reduces from six in early spermatids to four in mature spermatozoa. Each spermatozoon has an ovoid head with the acrosome 1.4?±?0.1?µm long and 1.6?±?0.1?µm wide and the nucleus 1.7?±?0.1?µm long and 2.3?±?0.1?µm in diameter, four spherical mitochondria, two centrioles oriented perpendicular to each other, putative glycogen in the shape of dense granules in the midpiece, and a flagellum with 9?×?2?+?2 organization of microtubules. The acrosome is a complex heterogeneous structure with five ordered layers of different electron densities, lying in a shallow depression on the anterior end of the nucleus. The nucleus is barrel-shaped (truncated ovoid) with the centriolar fossa housing the distal and proximal centrioles. Spermiogenesis and ultrastructure of spermatozoa of A. oxycephala are similar to those of another free spawning spionid, Marenzelleria viridis. Aonides and Marenzelleria have not, however, been considered as closely related taxa; thus, similarity in the morphology of their sperm might result from convergence or parallelism.     

The spermatozoon of the Echiniscidae (Tardigrada,Heterotardigrada) and its phylogenetic significance

The spermatozoon ultrastructure of four species of moss-dwelling Heterotardigrada belonging to four genera of Echiniscidae, namely Pseudechiniscus juanitae, Echiniscus duboisi, Novechiniscus armadilloides and Antechiniscus parvisentus, was investigated. In all species, the testicular male gamete is similar in morphology and in length. The spermatozoon is made up of a long head, consisting of a cylindrical acrosome and an oval or rod-shaped nuclear region which contains a nucleus with osmiophilic and electron-dense chromatin, and a tapering tail, with a "9+2" axoneme. An elongated sack-like structure originates from the posterior part of the head, extending beyond the main axis of the cell and running parallel to the tail. It consists of two parallel tubular regions which sometimes form a strict double helix and contain two voluminous, "free" mitochondria with unmodified cristae. In addition, a voluminous vesicle is present laterally to the centriole or between the end of the nucleus and the beginning of the mitochondria, limited by two cytomembranes and filled with electron-lucent and granular material. The male gametes representative of these moss-dwelling Echiniscidae are very similar to the spermatozoa of the marine Echiniscoididae Echiniscoides sigismundi. This close similarity emphasises that habitat changes have had little influence on the organisation of the sperm cell representative of Echiniscoidea. Spermatozoon characters which could be useful for phylogenetic studies on Tardigrada are discussed.     

Surrogate production of genome-edited sperm from a different subfamily by spermatogonial stem cell transplantation

The surrogate reproduction technique, such as inter-specific spermatogonial stem cells (SSCs) transplantation (SSCT), provides a powerful tool for production of gametes derived from endangered species or those with desirable traits. However, generation of genome-edited gametes from a different species or production of gametes from a phylogenetically distant species such as from a different subfamily, by SSCT, has not succeeded. Here, using two small cyprinid fishes from different subfamilies, Chinese rare minnow (gobiocypris rarus, for brief: Gr) and zebrafish (danio rerio), we successfully obtained Gr-derived genome-edited sperm in zebrafish by an optimized SSCT procedure. The transplanted Gr SSCs supported the host gonadal development and underwent normal spermatogenesis, resulting in a reconstructed fertile testis containing Gr spermatids and zebrafish testicular somatic cells. Interestingly, the surrogate spermatozoa resembled those of host zebrafish but not donor Gr in morphology and swimming behavior. When pou5f3 and chd knockout Gr SSCs were transplanted, Gr-derived genome-edited sperm was successfully produced in zebrafish. This is the first report demonstrating surrogate production of gametes from a different subfamily by SSCT, and surrogate production of genome-edited gametes from another species as well. This method is feasible to be applied to future breeding of commercial fish and livestock.

     

MORPHOLOGICAL OBSERVATIONS ON THE SPERMATOZOA OF ECHINOTHURID SEA URCHINS*

The morphology of the spermatozoa of three species of echinothurid sea urchins, Asthenosoma ijimai, Araeosoma owstoni, Hapalosoma gemmiferum, was investigated by means of transmission and scanning electron microscopy. The spermatozoa of these three species of echinothurid sea urchins have similar fine structure, but they differ in several features from the more familiar regular sea urchins. 1) The external anatomy of the head region of the echinothurid spermatozoon is diagnostic in that it has a highly elongated head. 2) The spermatozoon of echinothurid sea urchins has a very long slender nucleus, protruding on its proximal end, so that the shape of the nucleus resembles a sperhead. 3) The acrosomal granule in the acrosomal vesicle of the echinothurid spermatozoon is not a mass of homogenous particulate material but an electron opaque rod condensed in the central part of the acrosomal vesicle. Scanning electron microscopic examination revealed that echinothurid spermatozoa form acrosomal processes similar to those of other regular sea urchins. 4) The basal body is situated just beneath the middle of the posterior protrusion of the nucleus. The distal centriole is located beside the basal body almost in contact with it. The axis of the distal centriole is almost but not quite parallel to that of the basal body. A satellite complex can be recognized around the posterior part of the proximal centriole.     

Polymorphism of spermatozoa in Largus rufipennis Laporte 1832 (Heteroptera: Pyrrhocoroidea: Largidae)

The production of polymorphic spermatozoa has been registered in various insect orders such as Diptera, Lepidoptera, and Hemiptera. In this work, morphology of two types of spermatozoa produced by Largus rufipennis was reported for the first time in the Largidae family. For this, techniques including optical and transmission electron microscopy were used. Spermatozoa measured, on the average, 260 and 200 μm, and both types possessed a nucleus measuring on the average 65 μm. No ultrastructural differences were observed between the two spermatozoa types from L. rufipennis. The head region is composed of an acrosome, a nucleus, and part of the centriolar adjunct. The centriolar adjunct is in parallel with the nucleus and followed by mitochondrial derivates. The flagellum consists of an axoneme (9 + 9 + 2 microtubules) and two mitochondrial derivatives; no other accessory bodies were observed. The mitochondrial derivatives are symmetric in size and diameter. A similar quantity of the two spermatozoa types was observed in the seminal vesicle (57% of the large type and 43% of the small type), while in the spermatheca of the female, the larger spermatozoa were preferentially stored (87%). These results permit discussions concerning of the species biology reproduction, most specifically sperm competition strategies.     

Sperm Ultrastructure of Two Mollusk Species Geukensia demissa and Modiolus modiolus (Mytilidae, Bivalvia)

Sperm ultrastructure was studied in two Atlantic species of bivalve mollusks Geukensia demissa and Modiolus modiolus (Mytilidae). These spermatozoa have a classic structure common for species with external fertilization: the head of the spermatozoon of G. demissa and M. modiolus consists of an acrosome, including an acrosomal vesicle and periacrosomal material, a nucleus, and a middle part with two mutually perpendicular centrioles, surrounded by a ring of spherical mitochondria. The spermatozoa of G. demissa and M. modiolus differ in the general shape and size of the head (M. modiolus, 5.8 × 4 m; G. demissa, 4.2 × 2.5 m), as well as the structure of the acrosome and the number of mitochondria (M. modiolus, 8–12; G. demissa, 5–6). The spermatozoa of the Atlantic species M. modiolus and M. modiolus (M. kurilensis) from the Sea of Japan are close in ultrastructure, but differ in the number of mitochondria. This could possibly be a reason to consider M. modiolus from the Sea of Japan as a separate subspecies, M. modiolus kurilensis. In ultrastructure, the spermatozoa of G. demissa differ significantly from the spermatozoa of M. modiolus, but are similar to the spermatozoa of species of the genus Brachidontes.     

Sperm ultrastructure and a new type of spermiogenesis in two species of Pimelodidae, with a comparative review of sperm ultrastructure in Siluriformes (Teleostei: Ostariophysi)

During spermiogenesis, the spermatids of the pimelodid species Pimelodus maculatus and Pseudoplatystoma fasciatum show a central flagellum development, no rotation of the nucleus, and no nuclear fossa formation, in contrast to all previously described spermatids of Teleostei. These characteristics are interpreted as belonging to a new type of spermiogenesis, named here type III, which is peculiar to the family Pimelodidae. In P. maculatus and P. fasciatum, spermatozoa possess a spherical head and no acrosome; their nucleus contains highly condensed, homogeneous chromatin with small electron-lucent areas; and a nuclear fossa is not present. The centriolar complex lies close to the nucleus. The midpiece is small, has no true cytoplasmic channel, and contains many elongate and interconnected vesicles. Several spherical to oblong mitochondria are located around the centriolar complex. The flagellum displays the classical axoneme (9+2) and no lateral fins. Only minor differences were observed among the pimelodid species and genera. Otherwise, spermiogenesis and spermatozoa in the two species of Pimelodidae studied exhibit many characteristics that are not found in other siluriform families, mainly the type III spermiogenesis.     

Sperm ultrastructure in two species of the polychaete genusHarmothoe (Polynoidae)

The structure of spermatozoa is described for two species of polynoid polychaete,Harmothoe imbricata andHarmothoe impar, from material fixed and examined by both scanning and transmission electron microscopy. The two species undergo spermiogenesis within discrete testes. The testis ofH. imbricata is shown to have a layer of epithelial cells which possess an outer cuticular layer and a microvillous inner surface. Spermatocytes of both species are spherical but there are marked differences in the shape and size of the spermatozoa of the two species.H. impar has a classical primitive spermatozoon with a rounded head (2 μm long) and a button-shaped acrosome. Fully differentiated spermatozoa ofH. imbricata are modified from the primitive form by having a long head (10 μm length) with a pointed acrosome about 6 μm in length. Spermatozoa ofH. imbricata have a ring of up to fourteen mitochondria around a centrally inserted flagellum at the posterior whereasH. impar has a ring of four or five spherical mitochondria. Spermiogenesis is well synchronised inH. imbricata but all developmental stages can be found simultaneously in the testis ofH. impar. The differences in sperm structure of the two species may be related to differences in breeding biology which are hitherto unknown.     

Brain anatomy of the marine tardigrade actinarctus doryphorus (arthrotardigrada)

Knowledge of tardigrade brain structure is important for resolving the phylogenetic relationships of Tardigrada. Here, we present new insight into the morphology of the brain in a marine arthrotardigrade, Actinarctus doryphorus, based on transmission electron microscopy, supported by scanning electron microscopy, conventional light microscopy as well as confocal laser scanning microscopy. Arthrotardigrades contain a large number of plesiomorphic characters and likely represent ancestral tardigrades. They often have segmented body outlines and each trunk segment, with its paired set of legs, may have up to five sensory appendages. Noticeably, the head carries numerous cephalic appendages that are structurally equivalent to the sensory appendages of the trunk segments. Our data reveal that the brain of A. doryphorus is partitioned into three paired lobes, and that these lobes exhibit a more pronounced separation as compared to that of eutardigrades. The first brain lobe in A. doryphorus is located anteriodorsally, with the second lobe just below it in an anterioventral position. Both of these two paired lobes are located anterior to the buccal tube. The third pair of brain lobes are situated posterioventrally to the first two lobes, and flank the buccal tube. In addition, A. doryphorus possesses a subpharyngeal ganglion, which is connected with the first of the four ventral trunk ganglia. The first and second brain lobes in A. doryphorus innervate the clavae and cirri of the head. The innervations of these structures indicate a homology between, respectively, the clavae and cirri of A. doryphorus and the temporalia and papilla cephalica of eutardigrades. The third brain lobes innervate the buccal lamella and the stylets as described for eutardigrades. Collectively, these findings suggest that the head region of extant tardigrades is the result of cephalization of multiple segments. Our results on the brain anatomy of Actinarctus doryphorus support the monophyly of Panarthropoda. J. Morphol. 275:173–190, 2014. © 2013 Wiley Periodicals, Inc.     

Dimorphism of Spermatozoa in the Sea Urchin Strongylocentrotus nudus

A phenomenon of dimorphism in spermatozoa has been revealed for the sea urchin Strongylocentrotus nudus. The spermatozoa are different in the configuration of the circular mitochondrion. The bulk of male gametes (73.4%) have a symmetrical mitochondrion, whereas the remainder spermatozoa (26.6%) have an asymmetrical one. No other ultrastructural differences in the structure of spermatozoa have been revealed. The two types of spermatozoa are supposed to represent different kinds of normal gametes capable of fertilization.     

Spermatozoa and spermatogenesis in the northern quahaug <Emphasis Type="Italic">Mercenaria mercenaria</Emphasis> (Mollusca,Bivalvia)

We studied the ultrastructure of spermatogenesis and spermatozoa in the northern quahaug, the clam Mercenaria mercenaria. Spermatogenetic cells gradually elongate. Mitochondria gradually fuse and increase in size and electron density. During spermatid differentiation, proacrosomal vesicles migrate towards the presumptive anterior pole of the nucleus and eventually form the acrosome. The spermatozoon of M. mercenaria is of a primitive type. It is composed of head, mid-piece, and tail. The acrosome shows a subacrosomal space with a short conical contour. The slightly curved nucleus of the spermatozoon contains fine-grained dense chromatin. The middle piece consists of a centriolar complex which is surrounded by four mitochondria. The flagellum has a standard “9 + 2” microtubular structure. The ultrastructure of spermatozoa and spermatogenesis of M. mercenaria shares a number of features with other species of the family Veneridae. M. mercenaria may be a suitable model species for further investigations into the mechanisms of spermatogenesis in the Bivalvia.