Ultrastructure of the mature spermatozoon of the musky rat-kangaroo, Hypsiprymnodon moschatus (Potoroidae: Marsupialia)

It is currently accepted that Hypsiprymnodon moschatus is a basal macropod, retaining several primitive features from the ancestral phalangeroid that gave rise both to modern possums and macropods. Sperm ultrastructure is frequently found to provide informative characters for phylogenetic analysis as these features are not strongly selected for and are thus unlikely to be confounded by effects such as convergence. Caudal epididymal biopsies were taken from two male H. moschatus and prepared for transmission and scanning electron microscopy in order to study mature spermatozoan ultrastructure. Within the diprotodont group, several features were found to be unique to H. moschatus. These were an unusual acrosome covering nearly 100% of the dorsal nuclear surface, a midpiece fibre network which is loose, indistinct and extends to the anterior‐most aspect of the midpiece, a nucleus that is very streamlined, while the principal piece is comparatively short, and a mitochondrial helix and annulus which are similar to those of dasyurids. Also reported is the presence of a fibrous network in the connecting piece, not previously reported for any marsupial.     

Ultrastructure of sperm development and mature sperm morphology in three species of commensal bivalves (Mollusca: Galeommatoidea)

Ultrastructural features of the ovotestes, spermatogenesis, and the mature sperm are described for three galeommatid bivalves, Divariscintilla yoyo, Divariscintilla troglodytes, and Scintilla sp., from stomatopod burrows in eastern Florida. All three species yielded similar results except with respect to mature sperm dimensions. The ovotestis contains three types of somatic cells within the testicular portion: flattened myoepithelial cells defining the outer acinal wall; underlying pleomorphic follicle cells containing abundant glycogen deposits; and scattered, amoeboid cells containing lysosomal-like inclusions which are closely associated with developing sperm. Early spermatogenesis is typical of that reported from other bivalves. In contrast, the late stages of spermiogenesis involve the migration and gradual rotation of the acrosomal vesicle, resulting in a mature acrosome tilted about 70° from the long axis of the cell. The mature sperm possesses an elongated, slightly curved nucleus; a subterminal, concave acrosome with a nipple-like central projection; five spherical mitochondria and two centnoles in the middlepiece; and a long flagellum. The rotational asymmetry and the presence of perimitochondrial glycogen deposits in these sperm are unusual in the Bivalvia and may be associated with fertilization specializations and larval brooding common among galeommatoideans.     

Fine structure of the spermatozoon of <Emphasis Type="Italic">Diopatra neapolitana</Emphasis> (Polychaeta,Onuphidae)

The identification of Diopatra species lacks of clear diagnostic features of taxonomic importance and the knowledge of their reproductive characters is scant. The spermatozoa of Diopatra neapolitana were ultrastructurally investigated by electron microscopy in order to correlate the mode of reproduction with sperm cells morphology. The mature male gamete has a depressed subspherical nucleus, a cone-like acrosome, and a long flagellum. The acrosome is conical in shape and radially symmetrical, with a base diameter twice the height. Within the acrosome vesicle, the basal region includes a very electron-dense thickened ring composed of paracrystalline substances. The subacrosomal space is filled with a poorly electron-dense material, with straight filaments axially arranged to form a perforatorium. The nucleus contains the complete axial canal, holding the hind perforatorium region. The middle piece consists of five mitochondria with well-distinct membranes and tubulo-vesicular cristae. Two centrioles are located perpendicularly to each other. The proximal one lies in the central fossa and the distal one, slightly eccentric to the sperm axis, anchors to the plasma membrane by nine satellite rays of the pericentriolar complex. The axoneme has a 9+2 arrangement of microtubules. In general, the spermatozoon of D. neapolitana conforms exteriorly to the typical ect-aquasperm; the acrosome complex ultrastructure, however, shows noticeable modifications from the basic form. This finding agrees with the previously observed reproductive pattern (broadcast spawning—free-swimming larvae) of D. neapolitana belonging to Santa Gilla population, and may be helpful to solve the taxonomic problems of the D. neapolitana complex as well.     

Fine Structure of Spermatozoa in Perkinsiana rubra and Pseudopotamilla reniformis (Sabellidae: Polychaeta)

The Perkinsiana acrosome is elongated, pointed and tapering, strengthened anteriorly by cortical rings of longitudinally running units. The Pseudopotamilla acrosome is cap-like and its apical region contains a laminar body with two electron densities, the laminae crossed by occasional lines of dislocation, as in a crystal. These apparently solid regions are closely followed by peripherally situated lucent zones. The zone in Pseudopotamilla contains tubules, which are very like those in Sabella sperm, except that they lack connections with the acrosome base. Both species are probably broadcast spawners and have nuclei, mitochondria, centrioles and flagella of the primitive type. This may, however, be a secondary reversion through neoteny.     

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     

The spermatozoa of three species of Xenotrichulidae (Gastrotricha,Chaetonotida): the two “dünne Nebengeisseln” of spermatozoa in Heteroxenotrichula squamosa are peculiar para-acrosomal bodies

The spermatozoa of xenotrichulid gastrotrichs have been studied with the aim of supplying further characters for the phylogenetic analysis of Gastrotricha and to assess the reported biflagellarity of Heteroxenotrichula squamosa. Three species have been examined, belonging to the two hermaphroditic genera of xenotrichulids. The spermatozoa are filiform cells characterized by a scarcely condensed nucleus followed by a single mitochondrion and a flagellum with large accessory fibers. These show an obliquely striated cortex and a core containing some dense material. In Heteroxenotrichula squamosa and Xenotrichula punctata there is also a simple acrosome flanked by two para-acrosomal bodies which are curious long extracellular structures formed by a pile of electron-dense disks connected by thin threads. Xenotrichula intermedia lacks both acrosome and paraacrosomal bodies. The sperm model of xenotrichulids is very different from that of the Macrodasyida and Chaetonotida so far studied, thus supporting an isolated position of the family. The oblique striation of the tail's accessory fibers is similar in to the one period and inclination of the strated cylinder of macrodasyid gastrotrichs, thus being the only spermatological character shared by the two gastrotrich taxa.     

Spermatogenesis and sperm ultrastructure in the polychaete genusOphryotrocha (Dorvilleidae)

The details of spermatogenesis and spermiogenesis are described forOphryotrocha puerilis. The ultrastructure of mature sperm is shown forO. puerilis, O. hartmanni, O. gracilis, O. diadema, O. labronica, andO. notoglandulata. Clusters of sixteen cells each are proliferated by two stem cells in each setigerous segment ofO. puerilis representing the very early stages of both oogenesis and spermatogenesis. In each spermatocyte-I cluster, the cells are interconnected by cytoplasmic bridges. Early, clusters are enveloped by peritoneal sheath cells. These transient gonad walls break down prior to meiosis. The meiotic processes may start in the clusters with the cells still interconnected, or during breakdown of the original cluster, giving rise to smaller subclusters of both spermatocytes I and spermatocytes II with various numbers of cells. Finally, spermatid tetrads are present. As spermiogenesis progresses, the tetrads disintegrate. Golgi vesicles in both spermatocytes and spermatids contain electron-dense material, presumably preacrosomal. The acrosome is formed by such vesicles. In the six species studied here, the acrosomes appear to be of a similar overall structure but are of different shape. Centrioles are usually located beneath the acrosome. The distal centriole forms the basal body of a flagellum-like cytoplasmic process. The microtubules of these flagellar equivalents do not show a normal ciliar arrangement. The flagellar equivalent appears to be non-motile. InO. hartmanni and inO. notoglandulata, a flagellar equivalent is missing. Microtubules originating from the proximal end of the distal centriole stretch to the nuclear envelope. This feature appears to be especially conspicuous inO. puerilis and inO. labronica. InO. labronica and inO. notoglandulata, bundles of microtubules paralleling the cell perimeter appear to stabilise the sperm. Various numbers of mitochondria are either randomly distributed around the nucleus or accumulate on one side, often directly under the acrosome. Parts of the present paper were presented at the 2^nd International Polychaete Conference, Copenhagen 1986 and at the 3^rd International Polychaete Conference, Long Beach, Ca. 1989.     

Ultrastructure of the Geogarypus nigrimanus Spermatozoon (Arachnida,Pseudoscorpionida)

The ultrastructure of the spermatozoon of Geogarypus nigrimanus (Arachnida, Pseudoscorpionida) is described. The spermatozoon is composed of a small elliptic nucleus, a short flagellum and a very long and complex acrosome. In the male genital ducts, as in other studied species of pseudoscorpions, the sperm components are rolled up to form a globular structure enclosed in a cyst wall. The Geogarypus spermatozoon with a reduced flagellum and a giant acrosome seems to be evolutionary more advanced than spermatozoa from other pseudoscorpions.     

Scanning electron microscopy of post-ejaculatory spermiogenesis in the tick Ornithodoros moubata

The final stages of spermiogenesis in ticks occur in the female genital tract. Scanning electron microscopy was used to follow the morphologic changes that occur in the sperm during this post-ejaculatory spermiogenesis in the African soft tick, Ornithodoros moubata, and to determine a time sequence for its occurrence in vivo. Characteristic features of the maturing and mature cell described include (1) differentiation and detachment of the operculum, (2) changes in cell shape corresponding to different developmental stages, (3) passive migration of the nucleus and acrosome from an anterior to a posterior position, and (4) eversion of that portion of the acrosomal canal containing the nucleus and acrosome. A possible fate for the remainder of the acrosomal canal is suggested by extrusion and detachment of spherical structures, the ‘posterior bubbles’, from the posterior end of the mature supermatozoon. A mechanism for cellular elongation resulting from contractions of the outer sheath is proposed.     

A comparative study on the fine structure of developing spermatozoa in the isopod,Oniscus asellus,and the amphipod,Orchestoidea sp.

Summary Developing spermatids and mature spermatozoa from the isopod, Oniscus asellus and the amphipod, Orchestoidea sp. have been examined with the light microscope and the electron microscope and have been found to have similar morphologies. As spermiogenesis proceeds the nucleus migrates to one pole of the spermatid at which point an acrosome, contiguous rod, and cross-striated tail develop. The acrosomal vesicle elongates to a cone-shaped, mature acrosome lying at the apex of a cross-striated tail and nucleus which are situated at approximate forty-five degrees to each other. The cross-striated tail originates as an evagination of the spermatid plasma membrane near the acrosomal vesicle. The tail eventually grows to lengths of four to five hundred microns. The mature, tail-like appendage is cross-striated at major 750 to 800 Å, and minor 125 to 150 Å, periodicities. When observed in vitro, mature sperm of both species appear non-motile.Possible homologies of this unusual spermatozoon with other types of spermatozoa are made and it is concluded that: 1) isopod and amphipod spermatozoa should be classified as non-flagellate; 2) the cross-striated tail, previously thought to be a flagellum, is a non-motile structure associated in development and possible function with the acrosome; and 3) the rodlike structure contiguous with the acrosome is similar to perforatoria described in some vertebrate sperm.Supported by U.S.P.H.S. Grant No. NB-06285 and Training Grant No. 5-Tl-GM-202. — The author wishes to express his grateful appreciation for the technical assistance given by Miss Ann Barnett during the course of this investigation.     

THE IMPORTANCE OF HYDROLYTIC ENZYMES TO AN EXOCYTOTIC EVENT, THE MAMMALIAN SPERM ACROSOME REACTION

The mammalian sperm acrosome reaction is a unique form of exocytosis, which includes the loss of the involved membranes. Other laboratories have suggested the involvement of hydrolytic enzymes in somatic cell exocytosis and membrane fusion, and in the invertebrate sperm acrosome reaction, but there is no general agreement on such an involvement. Although reference was made to such work in this review, the focus of the review was on the evidence (summarized below) that supports or fails to support the importance of certain hydrolytic enzymes to the mammalian sperm acrosome reaction. Because the events of capacitation, the prerequisite for the mammalian acrosome reaction, and of the acrosome reaction itself are not fully understood or identified, it is not yet always possible to determine whether the role of a particular enzyme is in a very late step of capacitation or part of the acrosome reaction. (1) The results of studies utilizing inhibitors of trypsin-like enzymes suggest that such an enzyme has a role in the membrane events of the golden hamster sperm acrosome reaction. The enzyme involved may be acrosin, but it is possible that some as yet unidentified trypsin-like enzyme on the sperm surface may play a role in addition to or instead of acrosin. Results obtained by others with guinea pig, ram and mouse spermatozoa suggest that a trypsin-like enzyme is not involved in the membrane events of the acrosome reaction, but only in the loss of acrosomal matrix. Such results, which conflict with those of the hamster study, may have been due to species differences or the presence of fusion-promoting phospholipase-A or lipids contaminating the incubation media components, and in one case to the possibly damaging effects of the high level of calcium ionophore used. The role of the trypsin-like enzyme in the membrane events of the hamster sperm acrosome reaction may be to activate a putative prophospholipase and/or to hydrolyse an outer acrosomal or plasma membrane protein, thus promoting fusion. A possible role of the enzyme in the vesiculation step rather than the fusion step of the acrosome reaction cannot be ruled out at present. (2) Experiments utilizing inhibitors of phospholipase-A₂, as well as the fusogenic lysophospholipid and cis-unsaturated fatty acid hydrolysis products that would result from such enzyme activity, suggests that a sperm phospholipase-A₂ is involved in the golden hamster sperm acrosome reaction. Inhibitor and LPC addition studies in guinea pig spermatozoa have led others to the same conclusion. The fact that partially purified serum albumin is important in so many capacitation media may be explained by its contamination with phospholipase-A and/or phospholipids. Serum albumin may also play a role, at least in part, by its removal of inhibitory products released by the action of phospholipase-A₂ in the membrane. The demonstration of phospholipase-A₂ activity associated with the acrosome reaction vesicles and/or the soluble component of the acrosome of hamster spermatozoa, and the fact that exogenous phospholipase A₂ can stimulate acrosome reactions in hamster and guinea pig spermatozoa, also support a role for the sperm enzyme. The actual site or the sites of the enzyme in the sperm head are not yet known. The enzyme may be on the plasma membrane as well as, or instead of, in the acrosomal membranes or matrix. A substrate for the phospholipase may be phosphatidylcholine produced by phospholipid methylation. It is possible that more than one type of ‘fusogen’ is released by phospholipase activity (LPC and/or cis-unsaturated fatty acids, which have different roles in membrane fusion and/or vesiculation. In addition to acting as a potential ‘fusogen’, arachidonic acid released by sperm phospholipase-A₂ probably serves as precursor for cyclo-oxygenase or lipoxygenase pathway metabolites, such as prostaglandins and HETES, which might also play a role in the acrosome reaction. Although much evidence points to a role for phospholipase-A₂, phospholipase-C found in spermatozoa could also have a role in the acrosome reaction, perhaps by stimulating events leading to calcium gating, as suggested for this enzyme in somatic secretory cells. (3) A Mg²⁺-ATPase H⁺-pump is present in the acrosome of the golden hamster spermatozoon. Inhibition of this pump by certain inhibitors of ATPases (but not by those that only inhibit mitochondrial function) leads to an acrosome reaction only in capacitated spermatozoa and only in the presence of external K⁺. The enzyme is also inhibited by low levels of calcium, and such inhibition, combined with increased outer membrane permeability to H⁺ and K⁺, and possibly plasma membrane permeability to H⁺ (perhaps by the formation of channels), may be part of capacitation and/or the acrosome reaction. The pH of the hamster sperm acrosome has been shown to become more alkaline during capacitation, and such a change may result in the activation of hydrolytic enzymes in the acrosome or perhaps in a change in membrane permeability to Ca²⁺. A similar Mg²⁺-ATPase has not been found in isolated boar sperm head membranes. However, that conflicting result could have been due to the use of noncapacitated boar spermatozoa for the preparation of the membranes or to protease modification of the boar sperm enzyme during assay. (4) Inhibition of Na⁺, K⁺-ATPase inhibits the acrosome reaction of golden hamster spermatozoa, and the activity of this enzyme increases relatively early during capacitation. A late influx of K⁺ is important for the acrosome reaction. However, this late influx may not be due to Na⁺, K⁺-ATPase, but instead may be due to a K⁺ permeability increase (possibly via newly formed channels) in the membranes during capacitation. It is suggested in this review that Na⁺, K⁺-ATPase has a role early in capacitation rather than directly in the acrosome reaction (although such a role cannot yet be completely ruled out). One possible role for the enzyme in capacitation might be to stimulate glycolysis (which appears to be essential for capacitation and/or the acrosome reaction of hamster and mouse spermatozoa). The function of the influx of K⁺ just before the acrosome reaction is probably to stimulate, directly or indirectly, the H⁺-efflux required for the increase in intraacrosomal pH occurring during capacitation. Direct stimulation of the acrosome reaction by a change in membrane potential resulting directly from K⁺-influx is not a likely explanation for the hamster results. However, the importance of an earlier membrane potential change, due to increased Na⁺, K⁺-ATPase during capacitation, and/or of later membrane potential changes resulting from the pH change, cannot be ruled out. Although K⁺ is required for the hamster acrosome reaction, other workers have reported that K+ inhibits guinea pig sperm capacitation. However, the experimental procedures used in the guinea pig sperm studies raise some questions about the interpretation of those inhibition results. (5) Ca²⁺-influx is known to be required for the acrosome reaction. Others have suggested that increased Ca²⁺-influx due to inhibition or stimulation of sperm membrane calcium transport ATPases are involved in the acrosome reaction. There is as yet no direct or indirect biochemical evidence that inhibition or stimulation of such enzymatic activity is involved in the acrosome reaction, and further studies are needed on those questions. (6) I suggest that the hydrolytic enzymes important to the hamster sperm acrosome reaction will also prove important for the acrosome reaction of all other eutherian mammals.     

Spermatozoon Ultrastructure of Two Holothurian Species of the Genus Cucumaria (Dendrochirotida,Holothuroidea) from the Sea of Japan

The ultrastructure of spermatozoa of Cucumaria japonica and a congeneric morphologically similar deep-sea species was studied. The spermatozoa of both C. japonica and C. conicospermium are similar to those of other holothurians: the acrosome is composed of an acrosomal granule and periacrosomal material; the centrioles lie at an acute angle to one another; and the proximal centriole is connected to the nuclear envelope by a flagellar rootlet. The spermatozoa of C. japonica differ from those of C. conicospermium in the shape of the head and the dimensions and position of the acrosome. In C. japonica, the acrosome is completely embedded in the nuclear fossa and measures 0.7 m. In C. conicospermium, only one-third of the acrosome is embedded in the nuclear fossa; this acrosome measures 1.3 m. A correlation between the structure of the sperm acrosome and that of the egg envelope is discussed.     

Spermatogenesis in Boccardiella hamata (Polychaeta: Spionidae) from the Sea of Japan: sperm formation mechanisms as characteristics for future taxonomic revision

Reunov, A.A., Yurchenko, O.V., Alexandrova, Y.N. and Radashevsky, V.I. 2009. Spermatogenesis in Boccardiella hamata (Polychaeta: Spionidae) from the Sea of Japan: sperm formation mechanisms as characteristics for future taxonomic revision. —Acta Zoologica (Stockholm) 91 : 477–456. To characterize novel features that will be useful in the discussion and validation of the spionid polychaete Boccardiella hamata from the Sea of Japan, the successive stages of spermatogenesis were described and illustrated. Spermatogonia, spermatocytes and early spermatids are aflagellar cells that develop synchronously in clusters united by a cytophore. At the middle spermatid stage, the clusters undergo disintegration and spermatids produce flagella and float separately in coelomic fluid as they transform into sperm. Spermatozoa are filiform. The ring‐shaped storage platelets are located along the anterior nuclear area. The nucleus is cupped by a conical acrosome. A nuclear plate is present between the acrosome and nucleus. The nucleus is a cylinder with the implantation fossa throughout its length and with the anterior part of the flagellum inside the fossa. There is only one centriole, serving as a basal body of the flagellum, situated in close vicinity of the acrosomal area. A collar of four mitochondria is located under the nuclear base. The ultrastructure of B. hamata spermatozoa from the Sea of Japan appears to be close to that of B. hamata from Florida described by Rice (Microscopic Anatomy of Invertebrates, Wiley‐Liss, Inc., New York, 1992), suggesting species identity of the samples from the two regions. However, more detailed study of Florida’s B. hamata sperm is required for a reliable conclusion concerning the similarity of these two polychaetes. In addition to sperm structure, features such as the cytophore‐assigned pattern of spermatogenic cell development, the synchronous pattern of cell divisions, the non‐flagellate early spermatogenic stages, and the vesicle amalgamation that drives meiotic cell cytokinesis and spermatid diorthosis will likely be useful in future testing of the validity of B. hamata and sibling species throughout the world.     

Chemical characterization of the component of the jelly coat from sea urchin eggs responsible for induction of the acrosome reaction.

Jelly coat, a multicomponent extracellular matrix surrounding the sea urchin egg, induces the acrosome reaction in sperm. The jelly coats of the four species studied, Arbacia punctulata, Strongylocentrotus purpuratus, Strongylocentrotus drobachiensis, and Lytechinus variegatus, were found to be very similar in chemical composition. A sialoprotein (approximately 20% of the mass of the jelly coat) and a fucose sulfate polysaccharide (approximately 80%) are the major macromolecular components of the jelly coat. The acrosome reaction inducing capacity resides solely in the fucose sulfate polysaccharide. Induction of the acrosome reaction ranges from highly species specific to nonspecific. Thus, A. punctulata and S. drobachiensis sperm are induced to undergo the acrosome reaction only with their homologous jelly coat, while S. purpuratus sperm react equally well with homologous or L. variegatus jelly coat, but not with A. punctulata jelly coat. L. variegatus sperm seem to be relatively nonspecific in response. Species-specific induction of the acrosome reaction resides solely in the fucose sulfate polysaccharide, suggesting that there must be structural differences in this polysaccharide in the various species. Therefore, in some species, fertilization appears to involve sperm-egg recognition at the level of the jelly coat as well as at the level of sperm-egg receptors.     

Ultrastructure of spermiogenesis and spermatozoa in Diurodrilus subterraneus (Polychaeta,Diurodrilidae)

Spermiogenesis in the polychaete species Diurodrilus subterraneus may be divided into six stages. These stages, as well as the ultrastructure of the mature spermatozoa, are described based on TEM studies. The spermatozoa are unusual in having a very large acrosome followed by a region containing the nucleus and several ovoid mitochondria. A secondary acrosomal membrane forms a manchette around the nucleus and mitochondria. In this region, the plasma membrane is modified, with many small, mushroom-shaped cytoplasmic processes, each including filaments. The flagellum may be divided into three sequential regions; the longest, middle one is covered by a helically arranged mucous coat. Spermatozoa of the type described here are unknown among polychaetes but show certain superficial resemblances to those in oligochaetes. The resemblance of the mushroom-shaped bodies to spermatozoal microvilli in certain gnathostomulids is discussed. The phylogenetic relationships of Diurodrilidae are considered on the basis of this new information.     

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.     

SPERMIOGENESIS IN BARNACLES WITH SPECIAL REFERENCE TO ORGANIZATION OF THE ACCESSORY BODY*

Ultrastructural changes during spermiogenesis in the barnacles, Balanus amphitrite albicostatus, Balanus tintinnabulum rosa, Balanus trigonus and Tetraclita squamosa japonica, and organization of the sperm with special reference to the accessory body were studied. The Golgi complex organizes both the acrosome and the accessory body at different stages during spermiogenesis; the former is formed at the mid-spermatid stage and the latter is formed at the late spermatid stage. The arrangement of the components in the mature filiform sperm is quite unique, with the acrosome, the basal body just behind the acrosome, the axial filament parallel to a long nucleus, and a slender long mitochondrion behind the nucleus. The sperm in the anterior and posterior half of the ejaculatory duct differ from each other in form in that the sperm in the anterior duct are not equipped with the accessory body and the sperm in the posterior duct are. The accessory body can be artificially broken down by some treatments (1 M urea, alkaline sea water: pH 9.0-9.7, low ionic concentration of sea water). The loss of the accessory body from the sperm is assumed to be related to the ferti-lizability of the sperm.     

Spermatogenesis in the earthwormMicrochaetus pentheri (Oligochaeta,Microchaetidae)

Summary Spermatogenesis inMicrochaetus pentheri (Microchaetidae) follows the familiar pattern known for other oligochaetes. Spermatogenic stages develop around an anucleate cytophore from which they separate as mature spermatozoa. During spermiogenesis the nucleus elongates and becomes surmounted by a complex, elongate acrosome; the flagellar axoneme develops from the distal centriole. The centriole is positioned posterior to the mid-piece, which consists of six mitochondria radially adpressed to form a cylinder about 2 m long.Microchaetus shows many plesiomorphic features in the structure of its acrosome, which are also seen in two other taxa of the Diplotesticulata,Haplotaxis (Haplotaxidae) andSparganophilus (Sparganophilidae, Aquamegadrili), each of which has the greatest number of plesiomorphies in spermatozoal characters in its group. The Aquamegadrili constitute the sister-group of the Terrimegadrili which contain the earthworm families including the Microchaetidae. The numerous symplesiomorphies in spermatozoal characters do not, however, establish monophyly of microchaetids with haplotaxids and sparganophilids. An apomorphy in the acrosome ofMicrochaetus is its greater length (3.8 m vs less than 1 m inHaplotaxis and 1.5 m inSparganophilus), in this respect resembling other investigated terrimegadriles, the lumbricids, hormogastrids and megascolecids. The axial rod of the acrosome ofMicrochaetus appears apomorphic relative to that ofHaplotaxis, Sparganophilus, lumbricids and megascolecids in lacking an anterior expansion, the capitulum. It ends posteriorly in a cylindrical body, somewhat resembling the node diagnostic of the axial rod of megascolecid earthworms.     

The sperm structure of <Emphasis Type="Italic">Galloisiana yuasai</Emphasis> (Insecta,Grylloblattodea) and implications for the phylogenetic position of Grylloblattodea

The sperm ultrastructure of the Grylloblattodea Galloisiana yuasai was described and the sperm characters were comparatively examined in several orthopteroid insect orders for inferring the phylogenetic placement of the Grylloblattodea. The spermatozoa of G. yuasai are joined in bundles (spermatodesms) containing 200 units. Major features of these spermatozoa include a monolayered acrosome, a 9+9+2 axoneme with 16-pfs accessory microtubules and expanded intertubular material, and an evident “centriole adjunct”. The diffused material observed between the axoneme and the mitochondrial derivatives is considered to be an extension of the three connecting bands observed in other orthopteroid taxa, similar to what happens in some orthopteran lineages. The presence of the connecting bands, even though modified in G. yuasai, suggests that the Grylloblattodea are to be placed in a clade with Mantophasmatodea, Mantodea and Orthoptera.