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.     

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.     

SPERM MORPHOLOGY IN SERPULORBIS AND DENDROPOMA AND ITS RELEVANCE TO THE SYSTEMATIC POSITION OF THE VERMETIDAE (GASTROPODA)

Electron microscopic observations on the euspermatozoa (fertilizingsperm) and paraspermatozoa (infertile sperm) of Serpulorbissp. and Dendropoma sp. suggest that the family Vennetidae (sensustricto) is not closely allied to any true cerithioidean family.Vermetid euspermatozoa strongly resemble those of a number ofother mesogastropod superfamilies including the Stromboidea,Epitonioidea, Naticoidea, Calyptraeoidea, Cypraeoidea, somerissooideans and littorinoideans, and even some neogastropodtaxa. Vermetid paraspermatozoa are anudeate, with one or moretails extending from both ends of a central body region. Incontrast, paraspermatozoa of true cerithioideans: (1) have tailsextending from only the posterior region of the ‘head’(2) usually retain a condensed nuclear remnant and (3) sometimespossess an acrosome-like structure at the head apex. These results,in conjunction with anatomical work by Morton, suggest thatthe Vennetidae should be removed from the Cerithioidea and placedprobably in its own superfamily (Vermetoidea Raphinesque, 1815)as practised by some recent workers. The Vermetoidea possiblyare associable with the Stromboidea/Calyptraeoidea/Hipponicoidea/Xeno-phoroideablock within the Mesogastropoda ^*Present address: Department of Zoology, University of Queensland,St. Lucia, 4067, Queensland, Australia     

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)     

Ultrastructure of euspermatozoa and paraspermatozoa in the volutid snail <Emphasis Type="Italic">Adelomelon ancilla</Emphasis> (Mollusca: Caenogastropoda)

The ultrastructure of the euspermatozoa and the paraspermatozoa is investigated in Adelomelon ancilla, through histological section observed by transmission electron microscopy. Euspermatozoa of A. ancilla consists of: (1) a conical acrosomal vesicle (with a short basal invagination, constricted anteriorly) which is flattened at the apex and associated with an axial rod, a centrally perforated basal plate and a short accessory membrane, (2) a rod-shaped, solid and highly electron-dense nucleus (with a short basal fossa containing a centriolar complex and a 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 (where the axoneme is sheathed by nine tracts of glycogen granules), (5) a dense annulus at the junction of the midpiece and glycogen piece, and (6) a short free tail region (where the axoneme is surrounded only by plasma membrane). We observed a parasperm in A. ancilla. This is vermiform in shape and is composed of multiple axonemes and extensive cytoplasm with numerous vesicles, and mitochondria are scattered inside the axonemes. Sperm of A. ancilla is characterized by the euspermatozoa type 2 and the paraspermatozoa morphology belongs to type 5. The U shaped electrodense mitochondrial element in the midpiece of the eusperm and the constriction in the acrosomal vesicle present in A. ancilla are exclusive. We suggest that these characteristics could have taxonomic importance, because these was observed in other volutids and have not been observed in the rest of caenogastropods studies. We consider that the morphology of paraspermatozoa in A. ancilla corresponds to the “lancet” type.     

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.     

THE COURTSHIP, PSEUDO-COPULATION BEHAVIOUR AND SPERMATOPHORE OF TURRITELLA COMMUNIS RISSO 1826 (PROSOBRANCHIA: TURRITELLIDAE)

Underwater field observations of reproductive behaviour in Turritellacommunis Risso were made in Killary Harbour on the west coastof Ireland during May and June in both 1986 and 1987. Thesesightings are documented and complemented by temperature, salinityand oxygen measurements, population structure, sex-ratio REMOTS®sediment profile imagery data and additional laboratory experimentationand observations. The population had a density of 639.5 individuals/m²at the study site with males comprising between 62.3 to 65.6%of the sexed population. Females were larger than males, thepopulation frequency distribution was negatively skewed andcharacterised by slow-growing, mainly adult individuals. Pseudo-copulationgroupings of 3 to 11 male specimens in star-shaped arrangementsappeared on the sediment surface in May and June as early summerbottom water temperatures increased above 10.0°C to 11.5°C.At its highpoint, c. 6 groups/m² were observed, with a meanof 5.9 males/grouping. Surface trails left by fertile malesindicated that they probably responded to a pheromone releasedby a passive fertile female lying within a radius of at least0.5 m. Smaller males were proportionately more active than largermales in sperm transfer. It was estimated that c. 15% of malesand 3% of females were synchronously fertile at the maximumobserved level of pseudocopulation activity. Laboratory observationsidentified the production of a complex doublewalled cylindricalspermatophore containing paired and unpaired euspermatozoa,and multiflagellate paraspermatozoa. Paired euspermatozoa weremost dominant and were arranged spirally at a 45° angleto the spermatophore axis. These were also frequently foundin morulae. An additional, spirallybound membranous tube exhibitingbulbous diverticula within the spermatophore contained paraspermatozoaonly. The observations confirm that sperm transfer is not apassive process as previously thought, and that the specieshas a far greater capacity for movement than was believed. Gregariousness,a noted feature among populations of turritellid species appearsto be a critically essential life strategy among these aphallic,internally-fertilising gastropods. Present address: Dr. J.J. Kennedy, Kantstrasse 38, 22089 Hamburg,Germany (Received 7 November 1994; accepted 15 March 1995)     

The functional significance of aperture form in gastropods

Aperture form of marine prosobranch gastropods has evolved under the influence of a number of different selective forces, including: generation of shell form; protection from predation; accommodation of the foot during clamping behavior: and accommodation of water currents in and out of the mantle cavity. Aperture form correlates positively with foot shape in most gastropods and foot shape, in turn, correlates moderately well with substrate preference. Almost all gastropods that have non-round apertures elongate the aperture parallel to the foot so that water currenth tend to flow anteriorly to posteriorly. Fresh-water pulmonates have responded to somewhat different stresses. They exhibit clamping behavior and thus show correspondence between foot shape and aperture shape. They show less apertural strengthening as crab (or crayfish) predation is less of a factor and presumably because calcium carbonate is less available. They also lack anterior-posterior apertural elongation due to the absence of water currents through their mantle cavity. Due to the absence of mantle cavity water currents and clamping behavior, terrestrial gastropods do not show the apertural modifications associated with these two factors. In addition. few adaptations of apertural form are present to resist predation. Instead, many of the apertural modifications of terrestrial pulmonates seem to be concer-ned with the problems of water loss during estivation.     

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.     

TRANSFER OF THE GASTROPOD FAMILY PLESIOTROCHIDAE TO THE CAMPANILOIDEA BASED ON SPERM ULTRASTRUCTURAL EVIDENCE

Using sperm ultrastructure the systematic placement and affinitiesof the caenogastropod family Plesiotrochidae are re-examined.The simultaneous hermaphrodite, Plesiotrochus crinitus Thiele,1930, produces both euspermatozoa (uniflagellate, fertile sperm)and paraspermatozoa (bi- or triflagellate, infertile sperm).Features of each type of sperm clearly indicate that the Plesiotrochidaeare closely related to the Campanilidae (Campaniloidea) andare not, as previously believed, referable to the superfamilyCerithioidea. Significant sperm synapomorphies of Plesiotrochus(Plesiotrochidae) and Campanile (Campanilidae) include the morphologyof the eusperm midpiece (seven to nine straight mitochondriasurrounded by a segmented, accessory sheath of membrane-boundvesicles) and morphology of the anucleate parasperm head (axialcore of mitochondria surrounded by a bilaterally symmetricalarrangement of axonemes and dense vesicles). The characteristicsubstructure of the cerithioidean eusperm midpiece (four straightmitochondria each containing parallel, cristal plates) is notobserved in Plesiotrochus or Campanile. Euspermatozoa of Plesiotrochusdiffer from Campanile principally in details of the acrosomalcomplex (Plesiotrochus with apical bleb, probable absence ofan accessory membrane; Campanile without apical bleb, accessorymembrane well developed), the transverse profile of all midpiecemitochondria (thin in Plesiotrochus; thick in Campanile), andmorphology of the annulus (double ring in Plesiotrochus; singlering in Campanile). In addition, all observed paraspermatozoaof Plesiotrochus are anucleate, whereas in Campanile anucleateand nucleate paraspermatozoa are present. On the basis of spermsynapomorphies of Plesiotrochus and Campanile, the Plesiotrochidaeare transferred from the Cerithioidea to the Campaniloidea. (Received 3 August 1992; accepted 18 September 1992)     

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.     

Ultrastructure of dimorphic sperm and seminal receptacle in the hermaphrodites Barrimysia siphonosomae and Pseudopythina ochetostomae (Bivalvia, Galeommatoidea)

The intertidal Bivalvia Barrimysia siphonosomae (Montacutidae) and Pseudopythina ochetostomae (Kelliidae) live commensally with Siphonosoma cumanense (Sipuncula) and Ochetostoma erythrogrammon (Echiura), respectively. Both bivalves are hermaphrodites although males and females may occur. Paired, pouch-shaped seminal receptacles are located in the suprabranchial chamber near the genital opening of both species. The interior of the receptacles of sexually mature individuals contains numerous non-epithelial cells separated by narrow spaces that serve as a depot for sperm cells. Specimens of both species produce two sperm morphotypes. Euspermatozoa are oblong with elongate conical acrosomes, and a middlepiece consisting of about eight long mitochondria spirally arranged to form a sheath surrounding the basis of the flagellum. The paraspermatozoa are vermiform, about 4 µm broad and longer (up to 240 µm) in B. siphonosomae than in P. ochetostomae (ca 150 µm). The anterior, bullet-shaped, 4.5- or 3.0-µm-long acrosome is located above an elongate, 4- to 6-µm-long subcylindrical nucleus. Adjacent to the nucleus occurs a bundle of approximately 25 (B. siphonosomae) or ca 10 (P. ochetostomae) flagella. The cytoplasm of the sperm body contains spherical lipid droplets, glycogen deposits and numerous membrane-bound spindle- to rod-shaped electron-dense granules. It is presumed that both sperm types aggregate to form spermatozeugmata. The presence of a combination of almost identical and highly specialised euspermatozoa and paraspermatozoa in species of the two genera qualifies these structures as strong synapomorphies. Pseudopythina, as presently defined, is considered paraphyletic.     

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).     

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).     

Sperm dimorphism and spermatozeugmata in the commensal bivalve Pseudopythina macrophthalmensis (Galeommatoidea, Kelliidae)

The bivalve Pseudopythina macrophthalmensis (Galeommatoidea) is a commensal with the crab Macrophthalmus convexus (Ocypodidae) in Okinawa Prefecture, Japan. It is a protandric hermaphrodite which incubates the 65-μm large ova in the suprabranchial cavity. The species produces two types of sperm, which were studied with the electron microscope. The euspermatozoon has an elongate 2.8-μm-long, pointed acrosome, a slender 12- to 13-μm-long nucleus and a middlepiece containing several closely packed mitochondria arranged as a 5.5- to 6.0-μm-long sheath around the basis of the flagellum. The paraspermato- zoon is vermiform, 220-μm-long and up to 5-μm-broad. Anteriorly there is a ca 7-μm-long bullet-shaped acrosome followed by a subcylindrical 3.0- to 4.7-μm-long nucleus. Adjacent to the nucleus occurs a bundle of 26–42 40-μm-long flagella. The cytoplasm is packed with spherical lipid droplets and ovoid granules of unknown composition. Sperm of both types aggregate to form spermatozeugmata, which were found in the posterior mantle cavity or in paired seminal receptacles. Within the receptacles the euspermatozoa dissociate themselves from the spermatozeugma and become attached to the epithelial lining of the receptacle whereas the paraspermatozoa presumably disintegrate. The possible significance of the two types of sperm is discussed in the light of their presumed functions in gastropods. Accepted: 9 November 2000     

SIZE AND SEX IN CYPRAEIDAE

Samples of Cypraea (Notocypraea) angustata Gmelin 1791 and ofCypraea errones L. 1758 have been measured, and the sex of theindividuals determined. The males of C. angustatawere foundto be significantly shorter than the females. Differences betweenother dimensions in this species, and between all dimensionsmeasured in C. errones, were of little significance It has recently been shown (Griffiths, 1961) that the malesof Umbilia hesitata Iredale were greater in length than thefemales. Other evidence in this paper, and some subsequent measurementsmade by Schilder and Schilder (1961) have suggested that theconverse might be true for some other species of CYPRAEIDAE Sample groups of shells of C. errones and C.(N) angustata havenow been measured. The shells were then cut open, and thesexof the animal determined by the presence or absence of a penis.The results are givenin Tables I and II (Received 10 March 1961;     

THE COMPOSITION OF PHOSPHATE GRANULES IN THE DIGESTIVE GLANDS OF MARINE PROSOBRANCH GASTROPODS: VARIATION IN RELATION TO TAXONOMY

The composition of some 1150 phosphate granules in the digestiveglands of over 40 species of marine prosobranch gastropods hasbeen surveyed using a simple preparation technique and semi-quantitativeSEM x-ray microanalysis. Spectral peaks for Mg, K, Ca, Mn, Feand Zn were compared to that of P. Four major types of phosphategranule can be recognised, each generally characteristic ofa taxonomic grouping: high Mg in archaeogastropods and littorinids,multiple metal in higher mesogastropods, and, in neogastropods,Mg-Ca in muricoideans and high Zn in buccinoideans. At leastone Conus species (C. ventricosus) has high-Mg granules. Somecauses of variation in granule composition are discussed: speculatively,it is suggested a palaeoenvironmental influence seems possible. (Received 5 November 1997; accepted 6 January 1998)     

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.      

DENSITY AND GROWTH OF FRESHWATER PROSOBRANCH SNAILS (BITHYNIA GRAECA AND VIVIPARUS CONTECTUS)IN RELATION TO WATER CHEMISTRY IN SERRES, NORTHERN GREECE

Population density and daily rate of growth in relation to waterchemistry in the prosobranch gastropods Bithynia graeca andViviparus contectus were studied in the artificial Lake Kerkiniand in the marshes of Strymonas River upstream of its entryto Lake Kerkini (Serres Macedonia, N. Greece) respectively.PO4-Pconcentration proved to be the most significant hydro-logicalparameter for the density and the rate of daily growth in B.graeca. The water variable which proved to be significant forthe density of V. contectus was dissolved oxygen.B. graeca iscapable of true tissue-degrowth (40% loss of tissue dry mass)with low mortality rate during winter. (Received 24 March 1994; accepted 9 January 1995)     

Ultrastructure of the Spermatozoon of an Opisthobranch, Tornatina sp. (Mollusca, Gastropoda, Retusidae)

The spermatozoon of Tornatina sp. has been studied with phase-contrast light microscopy and transmission electron microscopy. The head of the spermatozoon consists of an elongate acrosome which caps the apex of an unusually complex, helical nucleus. This elaborate nuclear morphology has not been previously reported, but possibly is found in other opisthobranch gastropod spermatozoa. An axoneme is inserted deeply into the base of the nucleus whilst posterior from the nucleus, the axoneme is ensheathed successively by the mitochondrial derivative (midpiece) and 'glycogen' granules (glycogen piece). The midpiece exhibits fine structure similar to that observed in other euthyneuran spermatozoa (paracrystalline and matrix materials) and possesses a single helical compartment filled with what are probably glycogen granules. A dense ring structure occurs at the junction of the midpiece and glycogen piece. The spermatozoon of Tornatina and other gastropods (prosobranch and euthyneuran) are compared.