Spermiogenesis and spermatozoa in the relict bivalve genus Neotrigonia: relevance to trigonioid relationships,particularly Unionoidea

Spermiogenesis and spermatozoa in the relict trigonioid genus Neotrigonia are examined ultrastructurally. Mature Neotrigonia spp. spermatozoa exhibit the following features: (1) a blunt-conical nucleus; (2) an acrosomal complex composed of discoidal vesicles (9 to 15) arranged as a thin layer over the nuclear apex; (3) five (rarely four) spherical mitochondria positioned in depressions at the base of the nucleus; (4) proximal and distal centrioles (surrounded by the mitochondria); (5) a satellite complex anchoring the distal centriole and flagellum to the plasma membrane; and (6) a single flagellum. Spermatozoa of unionoids examined to date (Unionidae and Hyriidae only) exhibit similar features, including a nucleus with a blunt apex capped by a thin acrosomal complex (showing up to three vesicles). Among the Bivalvia, only Neotrigonia spp. and unionoid sperm possess an acrosomal complex composed of multiple vesicles. These data suggest that the Trigonioidea and Unionoidea are phylogenetically linked, but further work particularly on primitive unionoids is required to determine if this relationship is one of common ancestry or whether the Unionoidea have in fact been derived from the Trigonioidea.     

Ultrastructure of spermiogenesis in the gastropodHeliacus variegatus (Architectonicidae), with description of a banded periaxonemal helix

Spermiogenesis and spermatozoa of the marine gastropodHeliacus variegatus Gmelin were examined using transmission electron microscopy (TEM). Mature spermatozoa are composed of an acrosomal vesicle, helical nucleus, elongate midpiece, annulus, glycogen piece and short end piece. The midpiece consists of a 9+2 axoneme, nine coarse fibres, and a banded helix, all enclosed by a continuous mitochondrial sheath (with multiple, helically coiled grooves). Anterior extensions of the mitochondrial sheath and banded helix form a double sheath around the basal half of the nucleus—an arrangement possibly unique in the Mollusca. During spermiogenesis, dense plaques delineating the anterior and posterior poles of the spermatid nucleus become attachment sites for the acrosomal vesicle and the axial complex (respectively). As the nucleus condenses and elongates, midpiece formation involves fusion of numerous, oblong mitochondria along the length of the axoneme. The coarse fibres and banded helix of the midpiece probably are derived through centriolar activity. Results of the study support inclusion of the Architectonicidae within the Heterobranchia, but in view of midpiece specializations, do not clarify the precise relationship of the family within this subclass.     

Dorippids are Heterotremata: Evidence from ultrastructure of the spermatozoa ofNeodorippe astuta (Dorippidae) andPortunus pelagicus (Portunidae) Brachyura: Decapoda

Ultrastructural comparison between the sperm of the dorippid crabNeodorippe astuta (Fabricius, 1793) and the portunidPortunus pelagicus (Linnaeus, 1766) from Queensland, Australia, supports placement of dorippids with portunids and their relatives in the heterotreme section of the Eubrachyura (the Heterotremata - Thoracotremata or the Oxyrhyncha - Cancridea - Brachygnatha assemblage) and not withRanina ranina (in the Archaeobrachyura or the Oxystomata). Similarities between spermatozoa ofN. astuta and ofP. pelagicus (and other Eubrachyura) andR. ranina include: the large spherical, multi-layered, capsule-bound acrosome vesicle; the electron-dense operculum capping the vesicle; an invaginated core, or perforatorium; concentric zonation of the contents of the vesicle; a layer of cytoplasm, between the acrosome vesicle and the nucleus, which contains mitochondria (mostly degenerating) and lattice-like lamellar complexes or membrane remnants; a diffuse nucleus which is bounded externally by a combined nuclear and plasma membrane and cups the scanty cytoplasm and the large acrosome vesicle; and lateral arms into which the chromatin extends. Characteristic eubrachyuran features of theN. astuta sperm absent fromR. ranina are the long perforatorium (short and conical with a unique subacrosomal chamber inR. ranina) extending almost to the operculum; presence in the perforatorium of longitudinally arranged convoluted tubules; a zone of acrosomal rays forming the outer part of an inner dense zone; the presence of a thickened ring surrounding the basal part of the perforatorium; and, basally, two centrioles (absent fromR. ranina but also from some eubrachyurans). The sperm ofN. astuta is more similar to that ofP. pelagicus than to that of other investigated Brachyura. A heterotreme status ofN. astuta is thus unequivocally supported. Both species lack the posterior median process seen in the nucleus of majids andR. ranina.     

Spermatozoa and spermatogenesis in a monoplacophoran mollusc,Laevipilina antarctica: ultrastructure and comparison with other Mollusca

Ultrastructural features of spermatozoa and spermatogenesis are described for the first time in a monoplacophoran and compared with data for other conchiferan molluses. Spermatozoa of Laevipilina antarctica Warén and Hain, 1992, are of the structurally simple, aquasperm type, featuring a conical acrosome, a compact nucleus with lacunae, a short midpiece and a single flagellum. The acrosomal vesicle shows an electron-dense inner zone, and a basal invagination (subacrosomal space) contains granular material but no axial rod. The nucleus exhibits a shallow indentation apically which contains subacrosomal material, and five (sometimes four) indentations posteriorly which partially accommodate the five (rarely four) midpiece mitochondria. Two centrioles are present, the distal connected to the annulus by satellite fibres and acting as a basal body for the flagellum (axoneme probably 9+2 structure). Spermatogonia, characterized by an oblong nucleus and one or two nucleoli, line the basal membrane of the testis wall; spermatids of varying stages of maturity occupy the remainder of the testis. Acrosome and flagellum production is already well advanced in spermatids and probably commences at the spermatocyte stage. Cytoplasmic bridges occur in all developmental stages, most visibly in spermatids. The spermatid chromatin condenses in large tracts, leaving electron-lucent lacunae. Mitochondria collect posteriorly and form, presumably by fusion, the five (or four) larger, spherical mitochondria which gather around the centrioles.     

Euspermatozoa and paraspermatozoa in the trochoid gastropodZalipais laseroni (Trochoidea: Skeneidae)

Pronounced sperm dimorphism is reported for the first time in the prosobranch order Vetigastropoda. Using transmission electron microscopy, it is demonstrated thatZalipais laseroni Kershaw (Trochoidea: Skeneidae) produces uniflagellate euspermatozoa (eupyrene, fertile sperm) and multiflagellate paraspermatozoa (oligopyrene, infertile sperm). Euspermatozoa show the following features: (1) a conical acrosomal vesicle; (2) a long tubular, helically coiled nucleus; (3) a short midpiece (mitochondrial sleeve surrounding a 3µm-long electron-dense rod); (4) a chambered body (? fused centrioles) continuous with the dense rod of the midpiece; (5) a flagellum (characterized by an electron-dense sheath surrounding and partly obscuring the central pair of tubules). Paraspermatozoa are composed of an elongate head (lacking an acrosomal complex), a short midpiece (centriolar rods interspersed with mitochondria), and a posterior tuft of flagella. The head consists of a rodshaped anterior body and a condensed nuclear remnant — the latter lodged in a shallow invagination of the anterior body. Multiple flagella are attached via centriolar rods to a layer of dense material lining the nuclear remnant membrane. During paraspermatozoan development, the nucleus partially degenerates, then condenses, while the endoplasmic reticulum (ER), apparently assisted by the Golgi complex, is responsible for production of numerous, electron-dense secretory vesicles. These vesicles subsequently fuse to form the elongate, anterior body of the head region. The ability of at least one line of trochoid gastropods to produce an oligopyrene, multiaxonemal paraspermatozoon, suggests that the Caenogastropoda (with this feature) might have been derived from the Vetigastropoda rather than from any other archaeogastropod source.     

Acrosome differentiation and the acrosome reaction in ascidian spermatozoa:<Emphasis Type="Italic"> Ascidiella aspersa</Emphasis> and<Emphasis Type="Italic"> Ascidia mentula</Emphasis> with some implications for tunicate phylogeny

The spermatozoa of both Ascidiella aspersa and Ascidia mentula have architectural features characteristic of ascidian spermatozoa that have previously been described. They have an elongated head (7 µm long for A. aspersa and 4 µm long for A. mentula), a single mitochondrion that is applied laterally to the nucleus and lacks a midpiece. The acrosome of A. aspersa spermatozoa is a flattened vesicle, about 200 nm×100 nm×40 nm (length, width and height). The acrosome of A. mentula spermatozoa consists of multiple vesicles; they are about 50 nm×50 nm×40 nm (length, width and height). During spermiogenesis in both species, several proacrosomal vesicles (50–70 nm in diameter) appear in a blister at the future apex of the spermatid. In A. aspersa, these vesicles fuse with each other to form a single acrosomal vesicle, while in A. mentula these vesicles do not fuse with each other, and form multiple acrosomal vesicles. In A. aspersa spermatozoa, calcium ionophore A23187 induces the acrosome reaction in which membrane fusion between the acrosomal apical membrane and the overlying sperm plasma membrane occurs along the peripheral margin of the acrosome, resulting in the release of a hybrid, membrane-bound, small vesicle. In A. mentula, multiple acrosomal vesicles disappear by releasing small vesicles after treatment with the calcium ionophore A23187; this also appears to be an acrosome reaction. This paper discusses the way in which acrosome structure and function may have changed during the evolution of the Tunicata.Communicated by T. Ikeda, Hakodate     

Fine structure of spermatids and sperm of Dolioletta gegenbauri and Doliolum nationalis (Tunicata: Thaliacea): implications for tunicate phylogeny

In Dolioletta gegenbauri and Doliolum nationalis, collected in 1987 in the bay of Villefranche-sur-mer (French Mediterranean Sea), spermiogenesis is essentially the same. Early spermatids have a round head, a flagellum arising from a single centriole with short microtubules at 45° to its base, several mitochondria, and an acrosome 50 nm thick and 250 nm long with its long axis parallel to the plasma membrane. The acrosomal contents are dense, with a central denser plate. The nuclear envelope next to the acrosome is thickened and concave. In elongating nuclei, strands of chromatin become oriented parallel to the length of the nucleus and then twist helically. Although the mitochondria surround the nucleus, they remain relatively short and do not fuse into a single mitochondrion as in sperm of other tunicates. In very late doliolid spermatids, the acrosome undergoes exocytosis, and exposes fibrous material that stays associated with the tip of the sperm; no acrosomal tubule forms. Exocytosis at this stage may be triggered by fixation. If so, exocytosis probably occurs naturally at some time before fusion of sperm and egg. Sperm have elongate heads (1 m×10 m), with the anterior two-thirds of the nucleus surrounded by mitochondria. Spermiogenesis in doliolids, compared to that in other tunicates, is most like that in solitary members of the class Ascidiacea, except that in the latter the sperm mitochondria fuse and the acrosome appears incapable of exocytosis. In contrast, previous work has shown that salps (class Thaliacea) and colonial didemnid ascidians have an acrosomeless sperm with a spiral mitochondrion, while the class Appendicularia has a sperm with a midpiece, a compact head and an acrosome capable of exocytosis and acrosomal tubule formation. By outgroup comparison with echinoderms and acraniates, appendicularian sperm are plesiomorphic within the Tunicata. Thus, gamete morphology indicates that (1) solitary ascidians and doliolids had a common ancestor, (2) the popular idea that doliolids gave rise to appendicularians is incorrect, and (3) the Thaliacea are polyphyletic, doliolids having arisen very early from the ascidian lineage and salps having arisen later.     

渔游蛇精子的超微结构

扫描电镜观察表明,渔游蛇（Ｎａｔｒｉｘ Ｐｉｓｃａｔｅｒ）精子总长度约１１０μｍ,分为头和尾两部分;头部呈前稍尖的细长圆柱形,略变曲,约长８．５μｍ,直径以经约０．６μｍ。尾部又分４段：颈段、中段、主段和末段;其与从不同之处是中段较长,约７３μｍ,占精子总长度的２／３多;线料体型鞘由近５００圈超过５０００个线粒体构成;透射电镜揭示了头部顶体体覆疬于核前约１／２;尾部颈段的结构较复杂,包括连接片的踝     

Spermatozoan ultrastructure and spermatogenesis in aplousobranch ascidians,with some phylogenetic considerations

Spermatozoa and some stages of spermatogenesis were studied for four species of aplousobranch ascidians. Spermatozoa of Clavelina lepadiformis (Müller) (family Clavelinidae) are plesiomorphous in that they have apical acrosomal vesicles and a moderately elongated, cylindrical nucleus. The elongated mitochondrion is twisted ea. 11/2 times around the nucleus. In their ultrastructural morphology, C. lepadiformis sperm conform in some respects to the least-derived ascidian sperm, those of the phlebobranch ascidian Ciona intestinalis L.; however, the sperm of Clavelina lepadiformis have two apomorphies not shared with those of Ciona sp.: (1) the mitochondrion of Clavelina lepadiformis is long and spiralled along the entire nucleus rather than being comparatively compact and not at all helical; (2) the mitochondrial cristae are elongated parallel to the long axis of the nucleus, whereas in Ciona sp. sperm the cristae are unmodified. In Distaplia sp., Aplidium sp. and Synoicum pulmonaria (Ellis and Solander) the spermatozoa are more derived and consist of a proximal cylindrical and a distal corkscrew-like part. The mitochondrion in Distaplia sp. and Aplidium sp. contains electron-dense material and extends in a long thread around the nucleus. In S. pulmonaria the mitochondrion surrounds the anterior part of the nucleus in mature spermatozoa, and an elongated, dense structure displaying fine striation is enclosed in the mitochondrion in late spermatids. The sperm ultrastructural morphology observed in this study is consistent with the majority view that clavelinids are closest to the ancestral ascidian but is also consistent with other conclusions, particularly that the Cionidae are closest to the stem ascidian.     

Spermiogenesis and sperm structure in the shrimp Parapenaeus longirostris (Crustacea: Dendrobranchiata): comparative aspects among decapods

Early spermatids of the dendrobranchiate shrimp Parapenaeus longirostris (Lucas, 1846) have a spherical nucleus with large patches of heterochromatin, surrounded by a cytoplasmic mass that contains the conspicuous proacrosomal vesicle. The highly polarized mid spermatid mainly consists of the nuclear region, displaying a discontinuous nuclear envelope, and a large proacrosomal vesicle located at the opposite side of the cell. The most recent spermiogenic transformations primarily concern elongation of the proacrosomal vesicle to form a tapering spike. This results in the typically tack-shaped sperm of natantian decapods. The initial steps of spermiogenesis in the two studied dendrobranchiates prove to be parallel to reptant spermiogenesis in some respects, namely rupture of the nuclear envelope, chromatin decondensation and differentiation of electron-dense regions within the proacrosomal vesicle content. Specifically, whereas the anteriormost condensation gives rise to the operculum in brachyurans, in dendrobranchiates it becomes the apical portion of the spike. Despite an unquestionable morphological similarity between the sperm of carideans and dendrobranchiates, spermiogenesis in both groups displays meaningful differences. Spermatids of caridean shrimps lack a distinct proacrosomal vesicle. In the course of spermiogenesis, the spike arises from aggregated cytosolic materials; hence it is not membrane-bound. Unlike in other decapods, caridean sperm do not undergo a conventional acrosome reaction, since exocytotic events are not involved in this process. The above arguments suggest that, in the Decapoda, separation into three sperm classes is more suitable than the two traditionally accepted classes. The dendrobranchiate and reptant sperm types share a number of spermiogenic and functional features, while the caridean sperm type appears to represent an independent evolutive line with regard to sperm development and function.     

Spermatogenesis inPyrosoma atlanticum (Tunicata: Thaliacea: Pyrosomatida): Implications for tunicate phylogeny

Colonies ofPyrosoma atlanticum were collected by submersible in October 1988 in the Caribbean Sea, and testes were studied by electron microscopy. Spermatogonia, spermatocytes and early spermatids have two centrioles. The proximal centriole subsequently disappears, its remains apparently persisting in the spermatozoon as dense material adjacent to the distal centriole, which gives rise to the axoneme. At the tip of early spermatids are several 50 nm proacrosomal vesicles, which disappear leaving no trace in early elongating spermatids. The spermatozoon lacks an acrosome and has a head 35µm long. The head is differentiated into a bulbous posterior portion 5µm long × 1µm wide, a thinner anterior portion 25µm long tapering from a width of 0.7µm to a width of 0.4µm, and a very thin anterior extension 5µm long × 0.5µm wide. At the start of elongation, the anterior extension begins to form just lateral to the proacrosomal vesicles as a spiral projection comprising part of the nucleus, covered by a thin sheath of cytoplasm. This sheath of cytoplasm undergoes a complex differentiation. Ultimately, the nucleus in the anterior extension is overlain by two membrane-bound sheaths of cytoplasm connected by a spiral flange of cytoplasm. Between these two sheaths is a spiral space, open to the exterior through a subterminal pore near the sperm tip. In early spermatids the mitochondria fuse into a single mitochondrion, which remains lateral to the nucleus. The cristae become modified late in spermatogenesis. Throughout elongation of the spermatid there are patches of dense material between the nucleus and mitochondrion. A manchette of microtubules transiently encircles the thin anterior portion of the nucleus during the last phase of elongation. A manchette is not present during most of elongation. In the spermatozoon the mitochondrion, which has reticulate cristae, spirals a few times about the nucleus and extends from the junction between the bulbous portion and the thinner anterior portion of the nucleus to the junction between the thinner anterior portion and the nuclear extension. Spermatogenesis inP. atlanticum, compared to that in other tunicates, most closely resembles that in colonial ascidians, and supports the majority view that pyrosomes arose from aplousobranch ascidians that lost their attachment to the substratum. Pyrosome sperm are more highly derived than doliolid sperm, which have an acrosome that is probably capable of exocytosis. When salp and pyrosome sperm are compared, both are highly derived, but neither shares any apomorphies with the other that it does not share with at least one other tunicate order. Thus, sperm morphology does not support the majority view that pyrosomes gave rise to doliolids and neither confirms nor denies the idea that pyrosomes are intermediate between aplousobranch ascidians and salps. Therefore, it is likely that the class Thaliacea is polyphyletic, with doliolids arising very early from the ascidian lineage and with salps and pyrosomes arising somewhat later.     

Spermatogenesis,sperm storage and comparative sperm morphology in nine species of Capitella,Capitomastus and Capitellides (Polychaeta: Capitellidae)

Light microscopy and transmission electron microscopy (TEM) were used to describe spermatogenesis and the morphology of mature sperm and sperm storage organs in five sibling species of Capitella, three species in the related genus Capitomastus, and one species in the genus Capitellides. These capitellids lack a well-developed testis, but young males have a few specialized regions of the peritoneum in the eighth setiger, where germ cells proliferate and spermatogonia are released into the coelom, and spermiogenesis is completed. Mature sperm are stored in the central regions of paired genital ducts (coelomoducts), which lie between the seventh and eighth setigers. The cells forming the walls of the coelomostome and central region of the duct are ciliated and have large glycogen deposits. The lumenal borders have extensive microvilli and there is evidence that they secrete glycogen-containing materials into the duct. All species have modified primitive sperm with a conical acrosome, elongated nucleus, and long middle piece extending along the proximal portion of the flagellum. A single ring-shaped mitochondrion encircles the centriolar region of the middle piece and the cytoplasm is filled with glycogen. The sperm of all nine species differ significantly in the lengths of their middle pieces, acrosomes and especially in their nuclear lengths. The nuclear lengths have a twofold range among the sibling species of Capitella and Capitomastus. Subtle differences in the shape and volume of the acrosomal vesicle and acrosomal space characteristic of the Capitella sibling species seem to correlate with a basic division of these species into those with diploid chromosome numbers of 20 or 26. Spermiogenesis, the number of sperm produced, and the method of sperm storage are appropriate for efficient sperm utilization in fertilization. No evidence indicates that spermatophores are formed and transferred between individuals and the method of sperm transfer is not understood. The differences in the dimensions and acrosome morphology of mature sperm, and the previously demonstrated specializations in the egg envelopes in the Capitella sibling species, are characteristic features of the reproductive isolation that exists among these capitellid species.     

Ultrastructure of the spermatozoa of Hymenosomatidae (Crustacea: Brachyura) and the relationships of the family

The spermatozoa of the genus Odiomaris Ng and Richer de Forges, 1996 (=Amarinus Lucas, 1980) have the components typical of eubrachyuran (Heterotremata + Thoracotremata) sperm, but differ significantly from all other investigated eubrachyurans in at least ten characteristics: (1) presence of an epiopercular dome; (2) separation of all but the central region of the operculum from the remainder of the acrosome by an infra-opercular rim; (3) the fact that the acrosome is smaller in volume than the nucleus; (4) the acrosome is strongly emergent from the nucleus, being surrounded only basally by nuclear material; (5) the cytoplasmic sheath, ending anteriorly with the nucleus, is also basal; (6) division of the acrosome contents into an inner and outer acrosome zone is scarcely apparent in longitudinal section as the inner zone is narrow and of doubtful homology; (7) the thin, putative inner acrosome zone is anteriorly almost septate owing to several longitudinal corrugations; (8) basally there is a unique “fringe zone”; (9) the acrosome, including the epinuclear dome, is longer than wide; (10) the unique helical and posterolateral disposition of the nuclear arms. From a purely spermatological viewpoint, Odiomaris (as exemplified by O. pilosus and O. estuarius), and provisionally the Hymenosomatidae, are thus excluded from the Thora- cotremata, in which they were formerly placed, nor are they readily placeable in the Heterotremata. Received: 30 December 1996 / Accepted: 4 February 1997     

Sex in the beach: spermatophores, dermal insemination and 3D sperm ultrastructure of the aphallic mesopsammic Pontohedyle milaschewitchii (Acochlidia, Opisthobranchia, Gastropoda)

Sperm transfer via spermatophores is common among organisms living in mesopsammic environments, and is generally considered to be an evolutionary adaptation to reproductive constraints in this habitat. However, conclusions about adaptations and trends in insemination across all interstitial taxa cannot be certain as differences in mode of insemination via spermatophores do exist, details of insemination are lacking for many species, and evolutionary relationships in many cases are poorly known. Opisthobranch gastropods typically transfer sperm via reciprocal copulation, but many mesopsammic Acochlidia are aphallic and transfer sperm via spermatophores, supposedly combined with dermal fertilisation. The present study investigates structural and functional aspects of sperm transfer in the Mediterranean microhedylacean acochlid Pontohedyle milaschewitchii. We show that spermatophore attachment is imprecise. We describe the histology and ultrastructure of the two-layered spermatophore and discuss possible functions. Using DAPI staining of the (sperm-) nuclei, we document true dermal insemination in situ under the fluorescence microscope. Ultrastructural investigation and computer-based 3D reconstruction from TEM sections visualise the entire spermatozoon including the exceptionally elongate, screw-like keeled sperm nucleus. An acrosomal complex was not detected. From their special structure and behaviour we conclude that sperm penetrate epithelia, tissues and cells mechanically by drilling rather than lysis. Among opisthobranchs, dermal insemination is limited to mesopsammic acochlidian species. In this spatially limited environment, a rapid though imprecise and potentially harmful dermal insemination is discussed as a key evolutionary innovation that could have enabled the species diversification of microhedylacean acochlidians.     

Spermatozoon structure of some North American prosobranchs from the families Lottiidae (Patellogastropoda) and Fissurellidae (Archaeogastropoda)

The spermatozoa of four species of the patellogastropod family Lottiidae (Lottia pelta, L. digitalis, L. strigatella, Tectura scutum) and one species of the archaeogastropod family Fissurellidae (Diodora aspera) were examined in 1990 using transmission electron microscopy. All have primitive or ect-aquasperm, typical of invertebrates using external fertilization. Sperm of the lottiid limpets are characterized by a 5 to 9 m-long head composed of a conical acrosome which constitutes >50% of the head length, and a cylindrical nucleus. The acrosome of all species of lottiids is differentiated internally, and has a posterior invagination 0.9 to 1 m in depth, into which an elongate acrosomal lobe protrudes. Between the posterior acrosomal lobe and the nucleus, the subacrosomal material is aggregated as a fibrous column. The midpiece of the sperm has a ring of 4 to 5 spherical mitochondria of 0.6 m diam, posterior to which is a collar of cytoplasm 1 m long, which sheaths the anterior portion of the axoneme. The size and morphology of the acrosome and large cytoplasmic collar clearly distinguish the spermatozoa of the Lottiidae from other families of Patellogastropoda. The sperm of D. aspera (Fissurellidae) is typical of the family of archaeogastropod; the head has a length to breadth ratio of 4:1, and the cylindrical nucleus is capped by a small acrosome, <25% of the total head length, which is deeply invaginated.     

Effects of self-fertilisation and other factors on the early development of the scallop Pecten maximus

Adult Pecten maximus (L.) were dredged off north-east Anglesey, Wales, UK, during 1981. A 2×5 factorial mating was carried out involving self- and cross-fertilisation and the use of stripped spermatozoa. Assessments of yield, normality, and larval size were made at the D larva stage and larval size and mortality were measured after a fortnight's growth of the veligers. Underlying genetic variation was evident at all stages, with egg and sperm generally having a significant interactive effect. Cultures sired with stripped spermatozoa had fewer larvae, with more abnormality, grew slower and suffered higher mortality than most other cultures. Larvae from selfed cultures grew significantly slower than all other larvae. Data from past larval cultures also show that selfed larvae have a reduced growth rate. it is suggested that stripped spermatozoa may interfere with egg and sperm interaction at fertilisation, thus reducing the viability of larvae. On the other hand, the poor growth rate of selfed larvae is probably due to overall reduced heterozygosity compared to outbred larvae.     

Symbiontic bacteria in the gut of the blood-sucking Antarctic fish parasite Gnathia calva (Crustacea: Isopoda)

Structure and ultrastructure of the digestive tract of the ectoparasitic stages of the Antarctic isopod Gnathia calva, collected in the Weddell Sea and around the Antarctic Peninsula in the 1984–1985 season, are briefly described. There are only two digestive glands, with an ultrastructure similar to that of other isopods. The gut is divided into six regions: oesophagus, stomach, dilatable reservior for sucked-in blood, sphincter, rectal vesicle with symbiontic bacteria, and rectum. The highly dilatable anterior hindgut (reservoir) takes part in the resorption of nutrients and stores lipids and glycogen. The rectal vesicle has an epithelium with all the features of an organ with high metabolism and the capacity for the transportation of small molecules. The surface is increased by irregular microvilli. A very thin intima and a basal labyrinth are present. The presence of symbiontic bacteria is discussed in correlation with the haematophagous nutrition of G. calva.     

除草剂乙草胺对非洲爪蟾性腺发育的影响

使用性腺发育对内分泌干扰作用敏感的两栖动物非洲爪蟾作为模型动物,通过考察性别比、性腺整体形态和组织学形态来揭示乙草胺对其性腺发育的影响,从而确定乙草胺是否具有内分泌干扰活性.46/47期蝌蚪经不同浓度(5μg·L-1、10μg·L-1、20μg·L-1)的乙草胺暴露处理至变态后1个月,在变态结束后3个月时,解剖性腺、鉴别雌雄并固定性腺做组织切片.实验中对照组所有性腺都为典型的卵巢或睾丸,雌性百分率为48.78%(20/41).而乙草胺暴露组却出现了明显的异常睾丸,其总体上是睾丸,但又带有部分卵巢的特征,在统计性别时将具有异常睾丸的爪蟾归为雄性.5μg·L-1、10μg·L-1、20μg·L-1暴露组的雌性百分率分别为:57.14%(24/42)、66.67%(22/36)、55.26%(21/38).虽经统计分析无显著性差异,但乙草胺暴露组中雌性多于雄性的趋势和出现带有雌性特征的雄性的现象,一定程度上却暗示了乙草胺可能对非洲爪蟾的性腺发育有雌性化作用.正常睾丸的组织学结构应有发育成熟的生精小管,其内有各个时期的精子囊和生精细胞及精子.但经乙草胺处理的爪蟾睾丸却表现出几种明显的异常:没有生精小管,相反却像发育早期的睾丸一样,充满大量的精原细胞,完全没有生精细胞和精子;有生精小管结构,但其内精子囊结构不明显,生精细胞少并且排列混乱,其间有很大的空隙;睾丸出现腔隙,并有大量体细胞存在,这种结构与57期的卵巢相似;睾丸中出现异常的生精细胞,与58期卵巢的卵细胞相似;睾丸组织中有明显的卵细胞散布.组织学研究发现的乙草胺导致的睾丸结构证明了乙草胺对非洲爪蟾的睾丸发育有抑制雄性化作用和雌性化作用,即乙草胺对非洲爪蟾的性腺发育有内分泌干扰作用.     

Structure of the sperm of some South African archaeogastropods (Mollusca) from the superfamilies Haliotoidea,Fissurelloidea and Trochoidea

The structure of the spermatozoa of 11 species from five families of archaeogastropod (Haliotidae, Fissurellidae, Trochidae, Turbinidae, Phasianellidae) has been examined using transmission electron microscopy. All sperm are of the primitive, or ect-aquasperm type and each species has a sperm head (nucleus and acrosome) with unique morphology. Furthermore, the results from the present study together with those published in the literature reveal that, although there are a few exceptions, the size (length to breadth ratio) and spape of the nucleus and acrosome of sperm of species within each family are similar. It is therefore possible to identify members of a family and differentiate between families using sperm morphology. The intrafamilial similarities and interfamilial differences in sperm structure indicate that a spermiocladistic study of the suborder Vetigastropoda could provide interesting insights into the phylogenetic relationships of this group.     

Ultrastructure of the mature spermatozoon of the coconut crabBirgus latro (Coenobitidae: Paguroidea: Decapoda)

The spermatozoon ofBirgus latro (Linnaeus, 1767) is approx 14µm in length. It is composed of a large multi-layered oblong-ovoid acrosome which is capped by a conical operculum and lies anterior to a small ring of cytoplasm and an amorphous nucleus which is drawn out into a series of arms or extensions. Originating from the cytoplasmic area are three further long microtubular arms. The sperm ofB. latro is very similar to the sperm of the only other genus in the Coenobitidae,Coenobita, of whichC. clypeatus is a representative species. They share a suite of ultrastructural characters including: a long, cylindrical, capsule-bound acrosome containing an inner acrosome core, a large acrosome ray zone and a thin outer acrosome zone; an apical operculum anterior to a subopercular zone divided into two areas of differing density; an invaginated perforatorial zone with a bipartite granular matrix; microvillus-like extensions of the inner acrosome core projecting into the perforatorial invagination; a ring of cytoplasm, around the base of the acrosome, containing numerous mitochondria, extensive lamellar systems and the bases of three microtubular arms; granular nuclear material forming irregular arms; and at the posterior portion of the cell membrane a combination of nuclear and plasma membranes. Some ultrastructural characters which separate the two genera are: a domed operculum inC. clypeatus as opposed to a conical one inB. latro; inB. latro there is some residual cytoplasm external to the operculum and centrioles are absent from the mature spermatozoon; inC. clypeatus the inner acrosome core does not appear to invest the perforatorium and a series of dense rods are found subjacent and internal to the operculum. Similarities between the two coenobitids are greater than those shared with the paguridEupagurus bernhardus. In this latter species, the acrosome is more ovoid than cylindrical and the acrosome zones are less conspicuous; the operculum is absent from the mature sperm (although present during spermiohistogenesis); no subopercular zone is present; the perforatorium contains longitudinally arranged microtubules and extends the full length of the acrosome; and the nuclear material does not form separate nuclear arms. Sperm ultrastructure supports monophyly of the Paguroidea, while distinguishing coenobitids from pagurids within this superfamily.