Ultrastructure and potential taxonomic importance of euspermatozoa and paraspermatozoa in the volutid gastropods Zidona dufresnei and Provocator mirabilis (Caenogastropoda, Mollusca)

The ultrastructure of mature spermatozoa is investigated for the first time in the Volutidae, based on the commercially significant South American species Zidona dufresnei (Donovan, 1823) (fresh material) and supplemented with observations on testicular (museum) material of the deep sea New Zealand species Provocator mirabilis (Finlay, 1926). Euspermatozoa of Z. dufresnei (ex sperm duct) consist of: (1) a tall-conical acrosomal vesicle (with short basal invagination, constricted anteriorly) which is flattened anteriorly and associated with an axial rod, centrally perforate basal plate and short accessory membrane; (2) a rod-shaped, solid and highly electron-dense nucleus (with short basal fossa containing centriolar complex and initial portion of a 9 + 2 axoneme); (3) an elongate midpiece consisting of the axoneme sheathed by 5–6 helical mitochondrial elements, each exhibiting a dense U-shaped outer layer; (4) an elongate glycogen piece (axoneme sheathed by nine tracts of putative glycogen granules); (5) a dense annulus at the junction of the midpiece and glycogen piece and (6) a short free tail region (axoneme surrounded only by plasma membrane). Paraspermatozoa of Z. dufresnei are vermiform and dimorphic: the first type contains approximately 14–20 axonemes (arranged peripherally and interspersed with microtubules) and numerous oblong dense vesicles, numerous less dense (round) vesicles, occasional, large lipid-like vesicles, and scattered mitochondria; the second type contains 25–31 axonemes (peripherally arranged, interspersed with microtubules), occasional mitochondria and extensive cytoplasm. Results obtained for P. mirabilis from testis material are essentially as observed in Z. dufresnei, although the euspermatozoan acrosome still has to achieve its compressed transverse profile. Observations on paraspermatozoa were limited by fixation quality of available (testis) tissues, but these cells are similar to the first type of Zidona paraspermatozoa. Although most of the euspermatozoal features are also observed in many neotaenioglossans and neogastropods, the U-shaped outer layer of each mitochondrial element has not previously been reported and may prove a diagnostic feature of the Volutidae, the subfamily Zidoniinae or possibly only the Zidonini (in which Z. dufresnei and P. mirabilis are currently placed).     

Euspermatozoa and paraspermatozoa in the volutid gastropod Odontocymbiola magellanica,Patagonia, Argentina,Southwestern Atlantic Ocean

Giménez J. 2010. Euspermatozoa and paraspermatozoa in the volutid gastropod Odontocymbiola magellanica, Patagonia, Argentina, Southwestern Atlantic Ocean. —Acta Zoologica (Stockholm) 92 : 355–362. The ultrastructure of mature spermatozoa and paraspermatozoa of Odontocymbiola magellanica is investigated. Euspermatozoa consist of: (1) a tall, conical acrosomal vesicle (with a short basal invagination, constricted anteriorly); (2) a rod‐shaped, solid and highly electron‐dense nucleus; (3) an elongate midpiece consisting of the axoneme sheathed by helical mitochondrial elements each exhibiting a dense U‐shaped outer layer; (4) an elongate glycogen piece; (5) a dense annulus at the junction of the midpiece and glycogen piece; and (6) a short free‐tail region. Paraspermatozoa of O. magellanica are vermiform and dimorphic. First type contain approximately 14–17 axonemes (arranged peripherally and interspersed with microtubules) and numerous oblong dense vesicles, numerous less dense (round) vesicles, and scattered mitochondria; the second type contains 38–45 axonemes peripherally arranged and closer to the core region of the cell and occasional mitochondria. Most of the euspermatozoal features of O. magellanica are also observed in many neotaenioglossans and neogastropods. However, the U‐shaped outer layer of each mitochondrial element has only been previously reported in the Volutidae subfamily Zidoniinae. It is now reported here in the subfamily Odontocimbiolinae and may prove to be a diagnostic feature of the Volutidae family.     

Ultrastructure of euspermatozoa and paraspermatozoa in the marine gastropod Adelomelon beckii (Caenogastropoda, Volutidae)

The sperm morphology of Adelomelon beckii is described by optical and transmission electron microscopy. Both euspermatozoa and paraspermatozoa were found in the specimens studied. Euspermatozoa are filiform and have an elongate nucleus capped by an acrosome. A small basal plate lies between the base of the acrosome and the nucleus. The mid-piece consists of U-shaped mitochondria wrapped helically around the central axoneme. A dense annulus at the junction of the mid-piece and glycogen piece is found, ending in a short end-piece, composed of the axoneme surrounded by a plasma membrane. Two types of paraspermatozoa are found, both vermiform but differing internally with respect to the disposition and number of axonemes, as well as to the types of secretory vesicles. We suggest the use of paraspermatozoa as a systematic character to reveal phylogenetic relationships in this family.     

Ultrastructure of paraspermatozoa,euspermatozoa and eusperm-like spermatozoa ofObtortio cf.fulva (Prosobranchia: Cerithiacea)

The cerithiaceanObtortio cf.fulva produces three distinct types of spermatozoa: (1) paraspermatozoa, (2) euspermatozoa and (3) eusperm-like spermatozoa. Like most mesogastropods, euspermatozoa ofObtortio are composed of a conical acrosome, short posteriorly invaginated nucleus, elongate midpiece and glycogen piece, and short terminal region. The midpiece, however, is distinctly cerithiacean in structure and is composed of four non-helical midpiece elements. Eusperm-like spermatozoa closely resemble euspermatozoa, but have a very short nucleus only one half to one third the length of the euspermatozoon nucleus. Paraspermatozoa of this species are composed of (1) head (mosaic sheath of dense blocks enveloping multiple axonemes which attach anteriorly to a long apical structure), (2) midpiece (multiple axonemes interspersed with elongate mitochondria), and (3) multiple tail tuft (axonemes each ensheathed by glycogen granules). The possible role of eusperm-like spermatozoa is briefly discussed together with the taxonomic implications of the structure of the three sperm types.     

Ultrastructure of Euspermiogenesis in the Mesogastropod Stenothyra sp. (Prosobranchia, Rissoacea, Stenothyridae)

The structure of mature and developing euspermatozoa of the rissoacean gastropod Stenothyra sp. has been studied using transmission electron microscopy. During cuspermiogenesis nuclei pass through fibrillar and lamellar phases of condensation. A Golgi-derived acrosome attaches to the nucleus during the fibrillar phase. Spherical mitochondria of early euspermatids fuse to form the mitochondrial sheath which undergoes metamorphosis to form helical midpiece elements, paracrystalline material and helical midpiece compartments. Mature euspermatozoa consist of a flat acrosome (acrosomal cone, axial rod, basal plate), short curved nucleus (2.5–2.8 μm) and elongate midpiece and glycogen piece. Coarse fibres associated with the axoneme emerge from a posterior invagination of the nucleus and continue into the initial portion of the midpiece. In the proximal portion of the midpiece, two helical compartments (filled with membranous material) are present—only one of which persists further posteriorly. No compartments occur in the distal region of the midpiece. Posterior to the midpiece, the axoneme is surrounded by tightly-packed (glycogen) granules and terminates within this region. The distal end of the euspermatozoon consists solely of glycogen granules surrounded by the plasma membrane. Although coarse fibres (associated with the axoneme), midpiece paracrystalline material and helical compartments are commonly reported in sperm of euthyneuran gastropods, this represents the first report of all three features in any prosobranch euspermatozoon.     

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     

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.      

AN ULTRASTRUCTURAL STUDY OF EUSPERMATOZOA, PARASPERMATOZOA AND NURSE CELLS OF THE COWRIE CYPRAEA ERRONES (GASTROPODA, PROSOBRANCHIA, CYPRAEIDAE)

The sperm duct of the cowrie Cypraea errones Linné containseuspermatozoa, paraspermatozoa and nurse celts, the latter bearingclumps of attached euspermatozoa. Nurse cell/euspermatozoa associationshave been described in certain littorinacean gastropods, butare previously unrecorded in the Cypraeacea. Euspermatozoa ofC. errones resemble those of many other mesogastropods and someneogastropods (for example members of the Strombidae, Epitoniidae,Naticidae, Volutidae; shared features include structure of theacrosome, nucleus, glycogen piece, and helically coiled midpieceelements). However in C. errones, radially arranged paracrystallinefibres partly occupy the space between adjacent midpiece elements.Paracrystalline material is only rarely observed in spermatozoaof prosobranch gastropods and in all cases (including C. errones),is readily discernible form the complex paracrystalline layerspresent in the mitochondria) derivative of opisthobranch andpulmonate spermatozoa. Paraspermatozoa of C. errones are elongate,vermiform cells containing: multiple axonemes (bunched anteriorly,peripherally distributed posteriorly); granulated deposits (anteriorly);numerous dense vesicles (posteriorly) and scattered mitochondria(elongate, with parallel cristae). The axonemal attachment complexesfuse apically to form a sharp, conical structure. Comparisonwith available electron microscopic and light microscopic accountsof prosobranch euspermatozoa and paraspermatozoa suggests closeties between the higher Mesogastropoda (with which the Cypraeidaeshould be included) and the Neogastropoda. Further researchwill be required to determine whether the paracrystalline fibresobserved in euspermatozoa of C. errones are characteristic ofthe Cypraeidae or perhaps shared with the Ovulidae or Triviidae. (Received 26 November 1985;     

Euspermatozoa,Paraspermatozoa and Spermatozeugmata of Littoraria (Palustorina) articulata (Prosobranchia: Caenogastropoda) with Special Reference to the Pseudotrich

Abstract Paraspermatozoa and euspermatozoa of the littorinid gastropod Littoraria (Palustorina) articulata are examined using transmission electron microscopy and light microscopy. In the seminal vesicle, both sperm types occur, either as free cells or organized into spermatozeugmata. It is shown that the elongate (120–140 μm), flagellum-like component of the paraspermatozoon is in fact a tubular extension of the plasma membrane which encloses granular material but no axonemes or microtubules. This structure, here termed the pseudotrich, shows no evidence of motility and its function remains obscure. The main body region of the paraspermatozoon (length 32–36 μm) contains numerous spherical vesicles, scattered mitochondria, one or two large, rod-shaped bodies (length 20–24 μm) and a fusiform, granular body (containing DNA; probably a modified nucleus). The rod-shaped bodies, granular body and surrounding matrix are contained by a common membrane, and are therefore separated from other contents of the paraspermatozoon. In each spermatozeugma, euspermatozoa are attached via the tips of their acrosomes to the paraspermatozoan body at the opposite end to the pseudotrich. Euspermatozoa exhibit a conical acrosomal complex (with axial rod and basal plate), a tubular nucleus sheathing the axoneme, a midpiece (5–6 helical mitochondrial elements sheathing the axoneme), an annulus (with two rings), a glycogen piece and an end piece (total sperm length 268–272 μm). The euspermatozoa of L. articulata are similar to those of most littorinids and many other caenogastropods. The presence of a pseudotrich in the paraspermatozoon appears to be restricted to the subgenus Palustorina.     

EUSPERMATOZOAN ULTRASTRUCTURE IN BEMBICIUM AURATUM (GASTROPODA): COMPARISON WITH OTHER CAENOGASTROPODS ESPECIALLY OTHER LITTORINIDAE

Euspermatozoa of Bembicium auratum Quoy & Gaimard are examinedultrastructurally and compared with euspermatozoa of other caeno-gastropods,especially other species of Littonnidae The acrosomal vesicleis conical, deeply invaginated (accommodating an axial rod)and exhibits radial plates and a weakly developed apical bleb.Unlike euspermatozoa of the Littonmnae which have a long tubularnucleus (sheathing a significant portion of the axoneme), theeusperm nucleus of B. auratum is short, rod-shaped and solidwith the exception of a shallow centriolar fossa posteriorlyAvailable evidence suggests this is also the case for otherspecies of Lacuninae and for the Laevilitonninae The euspermmidpiece of B auratum consists of the axoneme and 7–9helically arranged mitochondria (containing short, randomlyarranged cnstae) Immediately posterior to the annulus, the axonemeis surrounded by nine tracts of glycogen granules to form theglycogen piece. The euspermatozoon terminates in a short endpiece, in which the 9+2 axoneme degenerates into isolated microtubules,only two of which survive to the posterior extremity of thecell Paraspermatozoa have not been observed in any species ofBembicium or in fact any other species of the Lacuninae, suggestingthat absence of paraspermatozoa is characteristic of the subfamily(contrasting with well developed round paraspermatozoa of theLittonninae) (Received 16 June 1994; accepted 26 July 1995)     

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     

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)     

Euspermatozoa and paraspermatozoa of the relict cerithiacean gastropod,Campanile symbolicum (prosobranchia,mesogastropoda)

Euspermatozoa and paraspermatozoa ofCampanile symbolicum Iredale, 1917 — a large, relict cerithiacean from Western Australia — have been examined using transmission electron microscopy and phase-contrast light microscopy. The euspermatozoa resemble those of many other mesogastropods with the important exception that the midpiece region exhibits unusual and possibly unique features. These include possession of seven or eight straight, periaxonemal elements (each containing scattered cristae) and a closely associated sheath composed of electrondense segments which are semicylindrical in shape and longitudinally aligned. This sheath — here termed the accessory midpiece sheath-surrounds only one half of the periaxonemal midpiece elements and lies outside the mitochondrial membrane (but nevertheless within the plasma membrane). Two types of paraspermatozoa occur inCampanile: (1) those with a nuclear core within the mosaic sheath of the head (nucleate paraspermatozoa) and (2) those lacking a nuclear core (dense blocks of mosaic sheath surrounding one to three axonemes — anucleate paraspermatozoa). An acrosome-like structure forms the apex of the head in both types of paraspermatozoa, while beyond the head region, electron-dense glycogen deposits are associated with each of the multiple tails. While the form ofCampanile paraspermatozoa suggests links with families such as the Cerithiidae, Potamididae and Turritellidae, the highly unusual morphology of the euspermatozoan midpiece indicates that the Campanilidae should occupy an isolated position within the superfamily Cerithiacea.     

The ultrastructure of spermatozoa and spermiogenesis in pyramidellid gastropods,and its systematic importance

Ultrastructural observations on spermiogenesis and spermatozoa of selected pyramidellid gastropods (species ofTurbonilla, Pyrgulina, Cingulina andHinemoa) are presented. During spermatid developement, the condensing nucleus becomes initially anterio-posteriorly compressed or sometimes cup-shaped. Concurrently, the acrosomal complex attaches to an electrondense layer at the presumptive anterior pole of the nucleus, while at the opposite (posterior) pole of the nucleus a shallow invagination is formed to accommodate the centriolar derivative. Midpiece formation begins soon after these events have taken place, and involves the following processes: (1) the wrapping of individual mitochondria around the axoneme/coarse fibre complex; (2) later internal metamorphosis resulting in replacement of cristae by paracrystalline layers which envelope the matrix material; and (3) formation of a glycogen-filled helix within the mitochondrial derivative (via a secondary wrapping of mitochondria). Advanced stages of nuclear condensation (elongation, transformation of fibres into lamellae, subsequent compaction) and midpiece formation proceed within a microtubular sheath (‘manchette’). Pyramidellid spermatozoa consist of an acrosomal complex (round to ovoid apical vesicle; column-shaped acrosomal pedestal), helically-keeled nucleus (short, 7–10 μm long, shallow basal invagination for axoneme/coarse fibre attachment), elongate helical midpiece (composed of axoneme, coarse fibres, paracrystalline and matrix materials, glycogen-filled helix), glycogen piece (length variable, preceeded by a dense ring structure at junction with midpiece). The features of developing and mature spermatozoa observed in the Pyramidellidae are as observed in opisthobranch and pulmonate gastropods indicating that the Pyramidelloidea should be placed within the Euthyneura/Heterobranchia, most appropriately as a member group of the Opisthobranchia.     

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 ultrastructure of the spermatozoon of Haplotaxis ornamentus (Annelida,Oligochaeta, Haplotaxidae) and its phylogenetic significance

Summary The spermatozoon of Haplotaxis ornamentus has characteristics common to all oligochaete sperm: filiform; primary acrosome vesicle carried on an acrosome tube and containing an axial rod (perforatorium) in an invagination (subvesicular space or secondary acrosomal invagination); an elongate, highly condensed cylindrical nucleus followed by a cylindrical midpiece of radially adpressed mitochondria not penetrated by the axoneme; a single (distal) centriole persistent, though modified, at maturity; axoneme with 9 doublets, each with two outer glycogen granules, and centrally two singlets accompanied by two solid fibres. A peculiar haplotaxid combination of characters (none unique) is slight withdrawal of the primary vesicle into the acrosome tube with a strongly emergent capitulate axial rod and moderately short midpiece. This ultrastructure is consistent with location of the Haplotaxidae at the base of the Haplotaxida (Haplotaxina — Alluroidina — Moniligastrina — Lumbricina). Tubificida sperm, although also plesiomorph for the Oligochaeta, have the autapomorphy elongate periaxial sheath (secondary tube), excepting the Phreodrilidae whose sperm show convergent resemblances to the Lumbricina. The term annuloid has been introduced for annulus-like structures of varied origins.     

Ultrastructure and Phylogenetic Significance of Notaspidean Spermatozoa (Mollusca, Gastropoda, Opisthobranchia)

Spermatozoa of five notaspidean opisthobranchs [Berthellina citrina, Berthella ornata, Pleuro-branchus peroni, Pleurobranchaea maculata, Umbruculum sinicum] were examined using TEM. In all five species, the acrosome (sensu lato) consists of an apical vesicle (the acrosomal vesicle) and acrosomal pedestal. The acrosomal pedestal overlaps the nuclear apex, and in P. peroni (and possibly B. ornata) is periodically banded—-the first reported incidence of this type of substructure in any euthyneuran acrosome. Although sperm nuclei of P. peroni, B. ornata and B. citrina differ in length and also the number of keels present (nucleus 7 μm long with four/five keels present in Pleurobranchus; 17 μm long with one keel in Berthella; 15 μm long with a very weak keel in Berthellina), the basal invagination to which the centriolar derivative, axoneme and coarse fibres are attached is always poorly developed, and very little overlap between nucleus and midpiece occurs. In P. maculata and U. sinicum, the nucleus forms a helical cord around the axoneme and mitochondrial derivative such that it is not possible to recognize exclusively ‘nuclear’ and ‘midpiece’ regions of the spermatozoon. In all notaspideans investigated, (1) the axoneme, coarse fibres and glycogen helix are enclosed by the paracrystalline and matrix components of the mitochondrial derivative and (2) a dense ring structure (attached to the plasma membrane) and glycogen piece are observed. While the glycogen piece is very short (0.85–1.43 μm) with a very degenerate axoneme in B. citrina, B. ornata and P. peroni, this region of the spermatozoan is well developed (30–35 μm long) in U. sinicum and exhibits a fully intact 9 + 2 axoneme. The ‘glycogen piece’(or its presumed homologue) in P. maculata spermatozoa is very short (0.65 μm), devoid of any axonemal remnant and constructed of a hollow, internal cylinder attached to an outer (incomplete) shell, and contains scattered (glycogen) granules. Spermatozoal structure supports a close relationship between the genera Berthellina, Berthella and Pleurobranchus. These three genera have more distant links with Pleurobranchaea, while Umbraculum maintains an isolated, specialized position within the Notaspidea.     

Ultrastructure of paraspermatozoa of cerithiacean gastropods (prosobranchia: Mesogastropoda)

Using transmission electron microscopy, paraspermatozoa of representative species of the families Cerithiidae, Potamididae, Planaxidae, Dialidae and the genusAustralaba (family position uncertain) have been examined and compared with those produced by other prosobranchs, particularly other investigated cerithiaceans. Special attention is focused on the phylogenetic importance of paraspermatozoa and euspermatozoa within the superfamily Cerithiacea. The paraspermatozoa of cerithiacean gastropods fall into two structural categories: (1) those with a head region and a tail tuft (number of tails and the length of the tail tuft variable — Cerithiidae, Planaxidae, Potamididae, Modulidae, Turritellidae, Campanilidae, Pleuroceridae,Obtortio, Australaba); and (2) those with an elongate, vermiform body filled with large electron-dense vesicles and up to ninety axonemes — the latter emerging as numerous short tails from the posterior half of the paraspermatozoon body (Dialidae).     

Sperm structure and sperm transfer in Pseudopythina subsinuata (Bivalvia; Galeommatoidea)

Males and females of the commensal protandric bivalve Pseudopythina subsinuata have paired seminal receptacles, the interior of which contains many slender elongate cells. The testis produces small euspermatozoa and comparatively few and much larger paraspermatozoa. The ?16-μm-long and 3-5-μm-thick paraspermatozoa have a terminally placed irregularly cork-screw-shaped acrosome and a bundle of ca. 16 flagella emerging from behind the nucleus. The role of the paraspermatozoa is obscure. Euspermatozoa are transferred to the seminal receptacles of the females and attach with the tip of the acrosome to the elongate cells. Most females contain one to three “sperm trees”, structures consisting of a short stem and numerous branches. They are firmly implanted in the abfrontal part of the gill filament and protrude into the posterior part of the suprabranchial (brooding) chamber. Implantation of the trees causes the gill tissue to swell around the stem and some of the nearest filaments to coalesce. All branches are densely coated with euspermatozoa that are attached by means of their acrosomes. It is conjectured that the syncytial and multinucleate trees arise from seminal receptacle cells that detach from the receptacle and thereupon fuse. A similar process is known in the allied P. tsurumaru, but the resulting structure (“sperm-carrying body”) is not attached to the gills.