Vergleichende Ultrastrukturuntersuchungen der Eu- und Paraspermien von 13Protodrilus-Arten (Polychaeta,Annelida) und ihre taxonomische und phylogenetische Bedeutung

The morphology of the slender, filiform spermatozoa of 13Protodrilus species of 22 different populations is investigated by light and transmission electron microscopy. All species have two types of spermatoza: fertile euspermatozoa, and paraspermatozoa, which are probably infertile and may comprise up to 20% of the total number of mature gametes. This is the first record of sperm dimorphism in polychaetes. The general construction pattern of the euspermatozoa is very complex. It shows a longish tapering acrosomal vesicle with an internal acrosomal rod, a rod-like conical nucleus, and a midpiece with numerous very complex supporting elements and two thin mitochondrial derivatives. Further, it has a ‘peribasal body’ surrounding the basal body of the axoneme, an anulus region with an ‘anchoring apparatus’ and an anulus cuff. Posteriorly, the tail region proper contains in some species 2 to 9 supporting rods. In several species the euspermatozoon shows very distinct and species-specific alternations of this ‘general pattern’ relating to e.g. size of sperm elements, structure of acrosome and nucleus, presence or absence of axial rod, and number, shape and size of supporting elements in midpiece and tail. In a number of species some sections of the euspermatozoon overlap with each other more or less strongly. The paraspermatozoon has a comparatively simple construction pattern and possesses no supporting structures in midpiece and tail region. The midpiece is very short and, in some species, entirely surrounded by its two thin and elongate mitochondrial derivatives. An axial rod is often missing or reduced; different sperm sections never overlap each other. In contrast to the euspermatozoa, the paraspermatozoa of the different species have a very similar ultrastructure. Their possible function in spermatophore transfer and histolytical opening of the female epidermis is discussed. A comparison of the different forms of euspermatozoa inProtodrilus elucidates possible plesiomorphous and apomorphous sperm traits. Very likely, the hypothetical plesiomorphous type of spermatozoa inProtodrilus has a very similar morphology to that of the paraspermatozoa, which for this reason are considered to be a sort of persisting representatives of the ancientProtodrilus sperm type. InProtodrilus, the different traits of the euspermatozoa represent excellent taxonomic characters for distinguishing species (e.g. ‘sibling species’). They can also be used well for phylogenetics within the genus, whereas the relations ofProtodrilus to other polychaete groups cannot be clarified solely on the basis of sperm characters, since in all groups the sperm structure is primarily an adaptation to a specific mode of reproduction. Generally, the value of sperm characters in phylogenetic considerations at higher taxonomic levels seems to be very limited due to the surprisingly wide range of different sperm structures within a single genus as is demonstrated in the present paper.      

Fine structure of the spermatozoon of Marthasterias glacialis (Linnaeus) (Echinodermata; Asteroidea), with special reference to acrosomal morphology

The sperm of Marthasterias glacialis (Linnaeus) was studied by light and electron microscopy. It is a long uniflagellated cell of the “primitive” type. The head has a spherical shape and contains a nucleus with a spheroid acrosome lying in a cup-shaped anterior fossa. The acrosome is formed by an acrosomal vesicle surrounded by the periacrosomal material. The basal specializations of the acrosomal vesicle show a clear differentiation of its constituents resembling the structure of membrane. The midpiece contains a very large annular mitochondrion which encircles two perpendicular centrioles. The distal centriole is in close association with a pericentriolar radial complex. The tail, containing a common microtubular axoneme, is projected to a variable position.     

Ultrastructure of spermiogenesis of Philippia (Psilaxis) oxytropis,with special reference to the taxonomic position of the architectonicidae (Gastropoda)

Summary Spermiogenesis of the architectonicid Philippia (Psilaxis) oxytropis was studied using transmission electron microscopy. Both spermatids and mature sperm of Philippia show features comparable to sperm/spermatids of euthyneuran gastropods (opisthobranchs, pulmonates) and not mesogastropods (with which the Architectonicidae are commonly grouped). These features include: (1) Accumulation of dense material on the outer membrane of anterior of the early spermatid nucleus — this material probably incorporated into the acrosome; (2) Structure of the unattached and attached spermatid acrosome (apical vesicle, acrosomal pedestal) accompanied by curved (transient) support structures; (3) Formation of the midpiece by individual mitochondrial wrapping around the axonemal complex, and the subsequent fusion and metamorphosis of the mitochondria to form the midpiece; (4) Presence of periodically banded coarse fibres surrounding the axonemal doublets and intra-axonemal rows of granules. A glycogen piece occurs posterior to the midpiece but is a feature observed in both euspermatozoa of mesogastropods (and neogastropods) and in sperm of some euthyneurans.Despite the lack of paracrystalline material or glycogen helices within the midpiece (both usually associated with sperm of euthyneurans), the features of spermiogenesis and sperm listed indicate that the Architectonicidae may be more appropriately referable to the Euthyneura than the Prosobranchia.Abbreviations a acrosome - ap anterior region of acrosomal pedestal - as support structures of spermatid acrosome - av apical vesicle of acrosome (acrosomal vesicle of un-attached acrosome) - ax axoneme - b basal region of acrosomal pedestal - c centriole - cf coarse fibres - cr cristal derivative of midpiece - db intra-axonemal dense granules - drs dense ring structure - gg glycogen granules - gp glycogen piece - G Golgi complex - m mitochondrion - mt microtubules - n nucleus - pm plasma membrane - sGv small Golgi vesicles     

Four lines of spermatid development and dimorphic spermatozoa in the sea urchin Anthocidaris crassispina (Echinodermata, Echinoida)

 The process of sperm development in the sea urchin Anthocidaris crassispina was studied by light and electron microscopy. Similar to other echinoids studied, a single flagellum, striated rootlet and nuage-like materials were present in spermatogonia of A. crassispina. Spermatocytes near the diplotene stage showed intracellular localization of the axoneme which appeared to be a retracted flagellum prior to cell division. Fibrous filaments were associated with a proximal centriole in spermatocytes and spermatids and might be involved in movement of the proximal centriole. An acrosomal vesicle was developed and a residual body was formed in spermatids. The special development patterns in A. crassispina attributed to the presence of two patterns of tail development and two patterns of mitochondrial development during spermiogenesis. These four lines of spermiogenesis resulted in the formation of four morphological types of sperm cell, i.e. sperms with: (1) a symmetrical midpiece and posterior tail, (2) an asymmetrical midpiece and posterior tail, (3) a symmetrical midpiece and bent tail and (4) an asymmetrical midpiece and bent tail. Sperm cells with bent tails (type 3+4) were probably still at the late spermatid stage because results of scanning electron microscopy demonstrated gradual detachment and eventual straightening of the bent tail, and their percentage occurrence in the sperm population decreased significantly (P<0.05) towards the spawning season of A. crassispina. Spermatozoa with a symmetrical midpiece were dominant (averaging 70% occurrence in the sperm population) over those with an asymmetrical midpiece. The dimorphic spermatozoa in A. crassispina (types 1, 2) are both considered to be euspermatozoa as their morphology is typical for Echinoida. Accepted: 4 May 1998     

An ultrastructural comparative study of the sperm of<Emphasis Type="Italic"> Hyla pseudopseudis</Emphasis>,<Emphasis Type="Italic"> Scinax rostratus</Emphasis>, and<Emphasis Type="Italic"> S. squalirostris</Emphasis> (Amphibia: Anura: Hylidae)

We make detailed comparisons of the ultrastructure of the spermatozoon among three species of the family Hylidae, Hyla pseudopseudis, Scinax rostratus, and S. squalirostris. The acrosome complex consists of two conical structures covering the nuclear rostrum, the acrosome vesicle, and the subacrosomal cone. The nucleus has a moderately condensed chromatin with a conical shape in longitudinal sections and a circular shape in cross-sections. In H. pseudopseudis, mitochondria are numerous and circular, and in S. rostratus and S. squalirostris there are fewer mitochondria that are more elongate in longitudinal and transverse sections. In H. pseudopseudis, the mitochondrial collar starts adjacent to the distal centriole, occupying the whole midpiece, whereas in both Scinax species the mitochondrial collar starts only at the posterior one-third of the midpiece. In both Scinax species, the presence of juxta-axonemal fiber, axial sheath, and axial fiber in the tail are seemingly plesiomorphic characters, widespread among bufonoid frogs. In H. pseudopseudis, however, the absence of axial fiber and axial sheath seems to be derived from the typical bufonoid condition. The differences between Hyla and Scinax sperm endorse the separation of the two genera and suggest that sperm ultrastructure can be a useful tool to investigate relationships at the intrafamily level.     

Ultrastructure of spermiogenesis in a freshwater stingray, Himantura signifer

Ultrastructural changes of spermatids during spermiogenesis in a freshwater stingray, Himantura signifer, are described. Differentiation of spermatids begins with modification of the nuclear envelope adjacent to the Golgi apparatus, before the attachment of the acrosomal vesicle. A fibrous nuclear sheath extends over the nuclear surface from the site of acrosomal adherence. The conical apical acrosome is formed during nuclear elongation. At the same time, chromatin fibers shift from an initially random arrangement, assume a longitudinal orientation, and become helical before final nuclear condensation. An axial midpiece rod is formed at the posterior end of nucleus and connects to the base of the sperm tail. Numerous spherical mitochondria surround the midpiece axis. The tail originating from the posterior end of the midpiece is composed of the usual 9 + 2 axoneme accompanied by two longitudinal columns, which are equal in size and round in cross section. The two longitudinal columns are absent at the end piece. A distinctive feature of freshwater stingray sperm is its spiral configuration.     

Preparation and ultrastructure of spermatozoa from green poison frogs, Dendrobates auratus, following hormonal induced spermiation (Amphibia, Anura, Dendrobatidae)

Few ultrastructural studies have been performed on members of the Dendrobatidae, although such investigations can be useful for the understanding of reproductive patterns, as a diagnostic method for males in breeding programs for endangered amphibians and for phylogenetic analysis. The sperm ultrastructure of the Green Poison Frog, Dendrobates auratus, from Panama is described following induced spermiation in living animals. To date only testicular spermatozoa in other dendrobatid frogs have been analysed. Moreover, an electron microscopic preparation method (transmission and scanning electron microscopy) for dendrobatid sperm cells in low concentration is presented. Sperm cells from stimulated frogs (100 IU human chorionic gonadotropin, hCG, twice at an interval of 1h) were recovered via cloaca lavage using 600 microl isotonic phosphate-free amphibian saline (IPS). Centrifuged flushings (5 min, 173 x g) were deposited on microscopic slides. Adherent spermatozoa were treated with Karnovsky fixative (overnight, 4 degrees C). After postfixation (2h, 1% osmium tetroxide), samples were dehydrated in series of ascending acetones (30-100%). For transmission electron microscopy sperm cells were encapsulated using Epon and 1.5% 2,4,6-tris(dimethylaminomethyl)phenol (DMP 30). Ultrathin sections (70 nm) were cut and stained with uranyl acetate (30 min) and lead citrate (5 min). Sperm cells are filiform with a 21.1+/-2.7 microm long and arcuated head and a single tail (35.0+/-4.2 microm length). Their acrosomal complex is located at the anterior portion of the head and consists of the acrosomal vesicle which has low electron density, and the subjacent electron-dense subacrosomal cone. In transverse section, the nucleus is circular (1.9+/-0.2 microm diameter) and conical in longitudinal section. It is surrounded by several groups of mitochondria. The chromatin is highly condensed and electron-dense but shows numerous electron-lucent inclusions. A short midpiece has a mitochondrial collar with a proximal and a distal centriole. The latter gives rise to the axoneme which alone forms the flagellum. The sperm ultrastructure of D. auratus differs from that of other Dendrobatidae because of the absence of a nuclear space and the absence of the undulating membrane associated with an axial fibre. This tail conformation is found in the Ranoidea but not in the Bufonoidea. These results show that the spermatozoa of D. auratus are the first within the Dendrobatidae without accessory tail structures. Methods of using sperm samples from hormonal treated frogs for ultrastructural studies is not only reasonable to examine e.g. amphibian phylogeny without killing frogs threatened with extinction but allows investigations in the field of assisted reproduction and male fertility for example in conservation programs for endangered amphibians.     

Intra-individual variation in sperm tail length in murine rodents

In eutherian mammals, there are marked interspecific differences in sperm head shape and tail length. In a few species, sperm head variability occurs but intra-individual variation in sperm tail length has rarely been investigated or commented upon. Here, we ask the question: Do murine rodent species that have variable sperm head shapes exhibit greater intra-individual variation in sperm midpiece and total tail lengths than closely related species where little, or no, sperm head variability occurs? From three separate lineages, we selected three pairs of murine rodents, one of which has monomorphic, and the other variable, sperm head shape. These were from southern Asia the bandicoot rats Bandicota bengalensis and Bandicota indica , from southern Africa the veld rats, Aethomys chrysophilus and Aethomys ineptus and from Australia the fawn hopping mouse Notomys cervinus and the spinifex hopping mouse Notomys alexis . Cauda epididymal sperm smears were prepared and sperm midpiece and total tail lengths were determined. A linear mixed-effects model was used to estimate intra-individual variance. The results showed that in all three species where there are variable sperm head shapes ( B. indica , A. ineptus and N. alexis ), statistically significantly greater intra-individual variability of sperm midpiece and total tail lengths occurs ( P <0.0001 in all cases). These species all have relatively smaller testes mass compared with the closely related species with monomorphic sperm populations. This suggests that depressed levels of intermale sperm competition may result in the occurrence of variability in not only the divergent sperm head shape but also in the length of the midpiece as well as that of the total length of the sperm tail.     

The sperm of Hylodinae species (Anura, Leptodactylidae): Ultrastructural characteristics and their relevance to interspecific taxonomic relationships

Aaabstract Hylodinae leptodactylids(sensu Lynch 1971) form a group of diurnal frogs, which is hypothesized on the basis of morphological traits to be the closest relatives of the dendrobatid frogs. Our study describes ultrastructural characteristics of sperm from three hylodine species(Hylodes phyllodes, Crossodactylus sp. n. andMegaelosia massarti) to reassess the intergeneric relationships within the Hylodinae, as well as the supposed relationship between the Hylodinae and Dendrobatidae. The ultrastructure of the sperm is very similar among the three species and is indicative of its conserved nature within the Hylodinae. The structure of the acrosomal complex was very similar to that of other leptodactylid species, to most of the remaining species included in the Bufonoidea lineage, and also to that observed in the dendrobatid species examined so far. Since such a structure has been considered a plesiomorphic trait, it contributes little to our understanding of the relationships between the Hylodinae and Dendrobatidae. The flagellar apparatus ofCrossodactylus sp. n. is very similar to that of most leptodactylids. The sperm ofMegaelosia massarti andHylodes phyllodes display a distinctive condition in their axial and juxtaxonemal fibers. This distinctive flagellar condition expands the already known variability in sperm structure within the Leptodactylidae.     

COMPARATIVE SPERM MORPHOLOGY OF THE PULMONATE LIMPETS TRIMUSCULUS COSTATUS, T. RETICULATUS (TRIMUSCULIDAE) AND BURNUPIA STENOCHORIAS AND ANCYLUS FLUVIATILIS (ANCYLIDAE)

Sperm ultrastructure is described for the first time in representativesof the pulmonate ‘limpet’ families Trimusculidae(Trimusculus costatus, T. reticulatus: marine) and Ancylidae(Burnupia stenochorias, Ancylus fluviatilis: freshwater). Allshow characteristic heterobranch sperm features (a spheroidalacrosomal vesicle supported by an acrosomal pedestal; a helicallykeeled nucleus and a complex, very elongate midpiece featuringparacrystalline and matrix layers sheathing the axoneme, coarsefibers and one or more glycogen helices). Posterior to the midpiece,a glycogen piece (axoneme sheathed by glycogen granules) andannulus are also present in all species. Taxonomically usefuldifferences in the shape and dimensions of the acrosome, nucleusand midpiece occur between the species. Results support thedecision of recent workers to transfer the Trimusculidae fromthe Siphonarioidea to a separate superfamily Trimusculoidea(characteristic sperm features including: narrow acrosomal pedestaloverlapping with nuclear apex; heavily keeled nucleus; midpiecewith strongly projecting secondary and glycogen helices). Therelationship of the Trimusculoidea to other pulmonates, as indicatedby sperm ultrastructure, remains uncertain largely because comparativedata for several important groups are unavailable. Spermatozoaof the two ancylids most closely resemble those of other investigatedplanor-boideans and to a lesser extent, those of the Lym-naeoidea.However, differences between Burnupia stenochorias (unique(?)accessory structure on the acrosomal pedestal; glycogen wedgeswithin the nuclear fossa; other features similar to planorbids)and Ancylus fluviatilis (all sperm features very similar toplanorbids) suggests that these patelliform ancylids are notclosely related. (Received 20 November 1997; accepted 23 January 1998)     

Fluorescent localization of thiols and disulfides in marsupial spermatozoa by bromobimane labelling

The acrosome of marsupial spermatozoa is a robust structure which, unlike its placental counterpart, resists disruption by detergent or freeze/thawing and does not undergo a calcium ionophore induced acrosome reaction. In this study specific fluorescent thiol labels, bromobimanes, were used to detect reactive thiols in the intact marsupial spermatozoon and examine whether disulfides play a role in the stability of the acrosome. Ejaculated brushtail possum (Trichosurus vulpecula) and tammar wallaby (Macropus eugenii) spermatozoa were washed by swim up and incubated with or without dithiothreitol (DTT) in order to reduce disulfides to reactive thiols. Spermatozoa were then washed by centrifugation and treated with monobromobimane (mBBr), a membranepermeable bromobimane, or with monobromotrimethylammoniobimane (qBBr), a membrane-impermeable bromobimane. Labelled spermatozoa were examined by fluorescence microscopy and sperm proteins (whole sperm proteins and basic nuclear proteins) were analysed by gel electrophoresis. The membrane-permeable agent mBBr lightly labelled the perimeter of the acrosome of non-DTT-treated possum and wallaby spermatozoa, indicating the presence of peri-acrosomal thiol groups. After reduction of sperm disulfides by DTT, mBBr labelled the entire acrosome of both species. The membrane-impermeable agent qBBr did not label any part of the acrosome in non-DTT or DTT-treated wallaby or possum spermatozoa. Thiols and disulfides are thus associated with the marsupial acrosome. They are not found on the overlying plasma membrane but are either in the acrosomal membranes and/or matrix. The sperm midpiece and tail were labelled by mBBr, with increased fluorescence observed in DTT-treated spermatozoa. The nucleus was not labelled in non-DTT or DTT-treated spermatozoa. Electrophoretic analysis confirmed the microscopic observations: Basic nuclear protein (protamines) lacked thiols or disulfide groups. Based on these findings, the stability of the marsupial acrosome may be due in part to disulfide stabilization of the acrosomal membranes and/or acrosomal matrix. In common with placental mammals, thiol and disulfide containing proteins appear to play a role in the stability of sperm tail structures. It was confirmed that the fragile marsupial sperm nucleus lacked thiols and disulfides. © 1994 Wiley-Liss, Inc.     

A phylogenetic analysis of Pleurodema (Anura: Leptodactylidae: Leiuperinae) based on mitochondrial and nuclear gene sequences,with comments on the evolution of anuran foam nests

Species of the genus Pleurodema are relatively small, plump frogs that mostly occur in strong‐seasonal and dry environments. The genus currently comprises 14 species distributed from Panama to southern Patagonia. Here we present a phylogenetic analysis of Pleurodema, including all described species and several outgroups. Our goals include testing its monophyly and the monophyly of the species groups that were historically proposed, and studying the evolution of some character systems, particularly macroglands and egg‐clutch structure; this last point also provided the chance for a discussion of foam nest evolution in anurans. Our dataset includes portions of the mitochondrial genes cytochromeb, 12S, 16S, and the intervening tRNA^Val; the nuclear gene sequences include portions of rhodopsin exon 1 and seven in absentia homolog I. Our results support a clade composed of Pleurodema and including the monotypic Somuncuria Lynch, 1978 nested within it. The latter genus is therefore considered a junior synonym of Pleurodema and its sole species is added to this genus. Furthermore, our results indicate the non‐monophyly of several species groups proposed previously. We recognize four clades in Pleurodema: the P. bibroni clade (P. bibroni, P. cordobae and P. kriegi), the P. thaul clade (P. bufoninum, P. marmoratum, P. somuncurensis and P. thaul), the P. brachyops clade (P. alium, P. borellii, P. brachyops, P. cinereum, P. diplolister and P. tucumanum) and the P. nebulosum clade (P. guayapae and P. nebulosum). Our results further indicate the need for a taxonomic reassessment of P. borellii and P. cinereum (as did previous studies), P. guayapae and P. nebulosum, and the three species in the P. bibroni clade. Pleurodema shows a striking pattern of variation in presence/absence of lumbar glands. Our results indicate multiple losses or independent gains of this character associated with defensive displays. The reproductive modes of Pleurodema include four different egg‐clutch structures. The optimization of these indicates that there are at least two independent transformations from the plesiomorphic mode of foam nests to egg‐clutch structures involving gelatinous masses of different sorts (ovoid plates, masses, or strings). We hypothesize that these independent transformations could involve changes at the behavioural (the loss of foam beating behaviour by the parent) and/or structural level (transformations involving the pars convoluta dilata, the section of the oviduct where the foam‐making substance is secreted). Finally, our study of foam nest evolution in Pleurodema is extended to the other groups of anurans where foam‐nesting occurs, on the basis of available data and recent phylogenetic hypotheses. In the different hyloid groups where it occurs, foam‐nesting evolved from clutches laid in water. However, in all ranoids in which foam‐nesting occurs, it evolved from terrestrial clutches, with eggs laid hanging in vegetation, or, if the clutches are laid on a restricted volume of water, involving endotrophic development. © The Willi Hennig Society 2012.     

Sperm ultrastructure of the Brazilian Amazon poison frogs Epipedobates trivittatus and Epipedobates hahneli (Anura, Dendrobatidae)

The sperm ultrastructure of Epipedobates trivittatus and E. hahneli is described. The spermatological characteristics are identical in both species, except for the extension of the acrosomal vesicle. The structure of the acrosomal complex is shared with species of the Bufonoidea neobatrachian lineage, which differs from the condition observed in species included in the ranoid lineage. The phylogenetic significance of the mitochondrial collar, also seen in Eubufonoidea groups, is still unclear. Also the significance of the alternative mitochondrial arrangement seen here is unclear. The perpendicular arrangement of the centrioles is also shared with the Bufonoidea and is considered a synapomorphic condition. An expanded undulating membrane and the absence of a juxtaxonemal fibre appear to be apomorphic characteristics of dendrobatid species, as also observed (homoplastically) for species of Litoria and Cyclorana. However, the notable expansion of the undulating membrane appears to be an autapomorphy of Dendrobatidae frogs. The ultrastructural data presented here do not support the proposed placement of E. trivittatus in a separate genus.     

Ultrastructure of Spermatozoa and Spermatids in Bonellia viridis and Hamingia arctica (Echiura) With Some Phylogenetic Considerations

Spermatozoa of the echiurans Bonellia viridis and Hamingia arctica show a similar ultrastructure. They are of a modified type. The head consists of a roughly cylindrical nucleus, which has a cover of electron-dense material. The acrosome is very large and consists of an acrosomal vesicle and a rod-shaped perforatorium or acrosomal rod. In close association with the nucleus, one or two mitochondria are found forming an irregular ring around the posterior tip of the nucleus and the centriolar apparatus. There are two centrioles, the proximal one with the conventional triplet microtubular structure. The tail flagellum is about 50 μm long and has the 9+2 axonemal structure. The oblique attachment of the acrosome to the anterior part of the nucleus gives the spermatozoon a bilateral symmetry. However, in the nuclear morphology, the arrangement of electron-dense material around the nucleus, in the mitochondria, and in the attachment of the tail flagellum, the spermatozoon shows asymmetric organization. The sperm structure in bonelliids is unique but its genesis and the morphology of the mitochondrial midpiece support the theory that the echiurans are related to the annelids. The main results of the study are summarized in Fig. 11.     

An ultrastructural examination of developing and mature euspermatozoa in pyrazus ebeninus (Mollusca,Gastropoda, Potamididae)

Summary Mature and developing euspermatozoa of the prosobranch gastropod Pyrazus ebeninus, have been examined using transmission electron microscopy and phase-contrast light microscopy. The head of the mature euspermatozoon consists of a conical acrosome capping a short, rod-shaped nucleus (laterally compressed posteriorly). A basal invagination in the nucleus contains the proximal portion of the axoneme and a dense attachment matrix. Four apparently non-helical mitochondrial elements (two large, two small) comprise the midpiece each being composed of curved, inclined cristal plates and a granular matrix. The structure and arrangement of the mitochondrial elements is thus distinguishable from the helical midpiece elements found in euspermatozoa of neogastropods and most mesogastropods and possibly is widespread in the Cerithiacea. A dense ring-like structure is found closely applied to the inside of the plasma membrane at the junction of midpiece and glycogen piece.Acrosome and midpiece formation and nuclear condensation have been studied in developing euspermatozoa. Acrosome development is divided into two phases: (1) a pre-attachment phase — during which a complex early acrosome is formed often at great distance from the nuclear apex, and (2) an attachment/post-attachment phase — during which the completed preattachment phase acrosome tilts into position at the nuclear apex and subsequently elongates. The nucleus passes through a recognizable sequence of condensation phases (reticular, fibrillar and lamellar phases). Microtubules surround both the nucleus and midpiece in the final phase of maturation. The four, elongate midpiece elements of the mature euspermatozoon are apparently derived from the four large, spherical mitochondria of the euspermatid.The potential usefulness of spermatozoal ultrastructure with regard to indicating affinities between groups of gastropod families is briefly discussed.Abbreviations a acrosome - ac euspermatozoon acrosomal cone - ar euspermatozoon axial rod - ax axoneme - bp basal plate - cy cytoplasmic droplet - cs cylindrical support structures of developing acrosome - dg dense granule of pre-attachment phase developing acrosome - dp dense plates of developing acrosomal cone - g glycogen granules - gp glycogen piece - G Golgi complex - j junction of midpiece and glycogen piece - l large midpiece element - m mitochondrion - M midpiece - mt microtubules - n nucleus - pm plasma membrane - sGv small Golgi vesicles - s small midpiece element     

The fine structure of the sperm of a holothurian and an ophiuroid

The fine structure of the mature sperm of the holothurian, Cucumaria miniata, and the ophiuroid, Ophiopholis aculeata, is described with particular reference to their acrosomal and centriolar satellite complexes, and compared to the sperm of other echinoderms. In Cucumaria, the acrosome is in the form of a diffuse acrosomal vesicle. It is unusual in that it apparently lacks an acrosomal membrane. A membrane separating the acrosomal vesicle from the periacrosomal material may not be equivalent to a typical inner acrosomal membrane. In Ophiopholis, the acrosome is dense, with some internal substructure, and is enclosed by a complete acrosomal membrane. In both species, the acrosome is partially surrounded by an amorphous periacrosomal mass. There is a notable absence of a subacrosomal depression and associated structures as found in other echinoderm sperm. The centriolar satellite complex (CSC) is essentially identical in both species. A reconstruction of the CSC is presented. The CSC consists of nine satellites radiating angularly from the distal centriole, each bifurcating at a dense node before inserting on a marginal ring containing circumferential microtubules. The ring is probably a cytoskeletal element. Immediately below the satellites are nine Y-shaped connectives. connecting each of the axonemal alpha doublets to the flagellar membrane.     

An ultrastructural examination of developing and mature paraspermatozoa in Pyrazus ebeninus (Mollusca,Gastropoda, Potamididae)

Summary The mesogastropod Pyrazus ebeninus, produces true spermatozoa (here termed euspermatozoa) and multi-flagellate, mobile cells (here termed paraspermatozoa). The mature paraspermatozoon consists of an elongateconical head (6.5–8.5 m in length), constructed of an electron-dense mosaic sheath surrounding a similarly dense, rod-shaped nuclear core (which runs almost the full length of the head). An acrosome-like structure forms the apex of the head. Five to eight axonemes are fixed to the posterior extremity of the nuclear core, each by means of an attachment complex (dense attachment rod, centriolar cap and centriole). A short (3–4 m) midpiece zone follows the head and consists of the multiple axonemes interspersed with very elongate mitochondria. A tuft of short (20 m) tails (termed minor tails) emerges from the midpiece in addition to one very long tail (termed the major tail) ensheathed in dense granules which resemble glycogen granules. A single membrane surrounds head, midpiece and tails whilst the nuclear core retains the original double nuclear membrane.Developmentally, the multiple axonemes arise from one of a pair of wheel-shaped arrangements of centrioles and attach to posterior indentations in the nucleus prior to its transformation into the nuclear core. Dense vesicles, derived apparently from the endoplasmic reticulum, accumulate along and around the developing nuclear core and (in the presence of microtubules) condense into the mosaic head sheath. Cytoplasmic mitochondria elongate and collect at the posterior axis of the cell, where, together with the axonemes, they form the midpiece.Features not previously reported in other ultrastructural studies of paraspermatozoa include the acrosome-like structure of the head, the structure of the midpiece zone, the glycogen sheath of the major tail, the dense annular structure at the junction of the midpiece and major tail and the presence of microtubules in the final phase of head and midpiece maturation. Some features of the euspermatozoon are also described and the comparative ultrastructure of mature and developing paraspermatozoa and their possible functions in the Gastropoda, are reviewed.Abbreviations ac euspermatozoon acrosomal cone - ar euspermatozoon axial rod - ax axoneme - b dense block of mosaic sheath - c centriole - cc centriolar cap - co cone of acrosome-like structure - dr dense attachment rod - dv dense vesicle - g glycogen granules - G Golgi complex - GER granular endoplasmic reticulum - H head of paraspermatozoon - m mitochondrion - M midpiece (euspermatozoon, paraspermatozoon) - maj major tail - min minor tails - mt microtubules - n nucleus - nc nuclear core - p dense plug of acrosome-like structure - pm plasma membrane - sGv small Golgi vesicles - Z transition of centriole to centriolar cap of attachment complex     

Ultrastructure of the sperm and spermatogenesis and spermiogenesis of Dina lineata (hirudinea,erpobdellidae)

The mature sperm of Dina lineata is of the modified type. The sperm are 48 μm long and 0.3 μm wide. The sperm are filiform and helicoidal cells with a distinct head, a midpiece, and a tail. There are two distinct regions in the head: the acrosome and the posterior acrosome, each with its own characteristic morphology. The midpiece is the mitochondrial region and has a single mitochondrion. Two distinct portions can be observed in the tail: the axonematic region and the terminal piece. In the process of spermatogenesis the early spermatogonia divide to form a poliplast of 512 spermatic cells. In the spermiogenesis the following sequential stages can be distinguished: elongation of the flagellum; reciprocal migration of mitochondria and Golgi complex; condensation of chromatin and formation of the posterior acrosome; spiralization of nuclear and mitochondrial regions; and, finally, formation of the anterior acrosome. The extreme morphological complexity of the Dina spermatozoon is related to the peculiar hypodermal fertilization which characterizes the erpobdellid family. Correlation between sperm morphology and fertilization biology in the Annelida is revised.     

Spermatology of Some Pycnogonida (Arthropoda), with Special Reference to a Microtubule-Nuclear Envelope Complex

The sperm cells of Nymphon leptocheles and N. rubrum are of the primitive type, which is a remarkable condition among arthropods. The motile sperm consist of a somewhat elongated head, a kind of midpiece and a long tail. An acrosome is absent. The nucleus is surrounded by longitudinally oriented microtubules running in furrows in the nuclear envelope. These microtubules are not interconnected by links or connected to the nuclear envelope; they persist in the mature sperm. No appreciable chromatin condensation takes place. The midpiece contains some unmodified mitochondria and a centriole. The tail is a simple, free flagellum. The results are in particular discussed in relation to other known microtubule-nuclear envelope complexes in sperm cells. The sperm cells of Pycnogonum littorale are, on the other hand, highly aberrant. They are unmotile, elongated cells containing a very high number (often more than 1000) of longitudinal microtubules arranged in complex patterns. Some folded membranes may represent the nuclear envelope. Other organelles are unidentificable or may be absent.     

Cauda epididymal spermatozoa of the rufous hare wallaby, Lagorchestes hirsutus (Metatheria, Mammalia) imaged by electron and confocal microscopy

The ultrastructure of mature Lagorchestes hirsutus spermatozoa is described for the first time, revealing unusual aspects of sperm structure in macropodid species. The sperm head is ovoid rather than cuneiform, lacks a ventral nuclear groove and has an acrosomal distribution over approximately 85–90% of its dorsal surface. Immediately adjacent to the nuclear membrane the peripheral nucleoplasm in most spermatozoa form an irregular series of distinctive evaginations previously not described in the spermatozoa of any other marsupial. The midpiece is extremely thickened and short, containing no helical network or peripheral plasma membrane specializations. Axonemal structure is unspecialized with no connecting lamellae; dense outer fibres are closely adherent to axonemal doublets. The sperm morphology of this species is highly aberrant in comparison to other macropod taxa and supports the retention of Lagorchestes as a distinctive genus. In light of this new information, skeletal and serological data should be re‐evaluated to determine the true taxonomic and phylogenetic position of this species.