Showing papers in "Journal of Molluscan Studies in 2013"

Lucinid bivalves from ancient methane seeps

Abstract: Twelve species of lucinid bivalves are reported from late Jurassic to late Miocene methane-seep deposits worldwide. Among them, eight species and two genera are new. Amanocina n. gen. includes Nipponothracia yezoensis from the Cenomanian of Japan as type species, Cryptolucina kuhnpassetensis Kelly, 2000 from the Berriasian of Greenland, A. raukumara n. sp. from the Albian of New Zealand and A. colombiana n. sp. from the Oligocene of Colombia. Tehamatea n. gen. includes Lucina ovalis Stanton, 1895 and Lucina colusaensis Stanton, 1895 from the late Jurassic to early Cretaceous of California, T. vocontiana n. sp. from the Hauterivian of southern Europe and T. agirrezabalai n. sp. from the Albian of northern Spain. The new species are: Cubatea awanuiensis from the Albian and Cenomanian of New Zealand, Nymphalucina panochensis from the early Palaeocene of California, Elliptiolucina washingtonia from the late Oligocene of Washington State, USA, and Elongatolucina peckmanni from the Oligocene of Colombia. New combinations are provided for Nipponothracia lomitensis (Olsson, 1931) from the Oligocene of Peru and Elliptiolucina hetzeli (Martin, 1933) from the late Miocene of Indonesia. The anterior adductor muscle scar of Beauvoisina carinata is documented for the first time. The lucinids found at Jurassic and Cretaceous deep-water methane seeps belong to the subfamily Myrteinae and within this to genera that are restricted to the seep environment (Beauvoisina, Tehamatea, Amanocina and Cubatea); shallow-water seeps were inhabited by the codakiine genus Nymphalucina, which is not seep-restricted. Amanocina, Cubatea and Nymphalucina survived into the Cenozoic. Genera that newly colonized deepwater seeps during the Cenozoic include members of both Myrteinae (Elongatolucina, Nipponothracia and Elliptiolucina) and Codakiinae (Epilucina and Lucinoma); the latter are clearly not seep-restricted.

Shifts in stable-isotope signatures confirm parasitic relationship of freshwater mussel glochidia attached to host fish

Abstract: The parasitic nature of the association between glochidia of unionoidean bivalves and their host fish (i.e. the role of fish hosts in providing nutritional resources to the developing glochidia) is still uncertain. While previous work has provided descriptions of development of glochidia on fish hosts, earlier studies have not explicitly documented the flow of nutrition from the host fish to the juvenile mussel. Therefore, our objective was to use stable isotope analysis to quantitatively document nutrient flow between fish and glochidia. Glochidia were collected from nine adult Lampsilis cardium and used to inoculate Micropterus salmoides (n ¼ 27; three fish per maternal mussel) that produced juvenile mussels for the experiment. Adult mussel tissue samples, glochidia, transformed juvenile mussels and fish gill tissues were analysed for d 15 N and d 13 C isotope ratios. We used a linear mixing model to estimate the fraction of juvenile mussel tissue derived from the host fish’s tissue during attachment. Our analyses indicate a distinct shift in both C and N isotopic ratios from the glochidial stage to the juvenile stage during mussel attachment and development. Linear mixing model analysis indicated that 57.4% of the d 15 N in juvenile tissues were obtained from the host fish. This work provides novel evidence that larval unionoideans are true parasites that derive nutrition from host fish during their metamorphosis into the juvenile stage.

Testing the influence of sediment depth on drilling behaviour of Neverita duplicata (Gastropoda: Naticidae), with a review of alternative modes of predation by naticids

Abstract: Predatory naticid gastropods typically attack other infaunal molluscs by drilling holes that record their activities in the shells of their prey. Other modes of naticid predation, which need not leave complete boreholes, have been noted in the literature and may complicate interpretation of the record of naticid predation in fossil and modern assemblages. ‘Smothering’ is an alternative form of predation that has never been defined clearly with respect to naticid gastropods. Feeding occurs in the absence of a completed drillhole; in most cases suffocation is implied, but reported deaths may be linked to an array of mechanisms (e.g. direct feeding, anaesthetizing mucus). We examine the pervasiveness of alternative modes of predation employed by naticids reported in the literature and offer recommendations regarding the terminology used in referring to such mechanisms. Because it is unclear if predatory behaviours such as suffocation are common in natural settings or are mostly artefacts of laboratory conditions such as insufficient substrate, we examined experimentally the influence of different sediment depths on drilling vs suffocation of Mercenaria mercenaria prey by Neverita duplicata. More than 99% (n ¼ 404) of the clams recorded as consumed in our experiments were drilled, regardless of sediment depth, with ,1% (n ¼ 3) noted as cases of potential suffocation. Our results indicate that shallower sediment depths do not affect drilling in this species. Analysis of previous studies indicates that prey health and other laboratory effects are likely responsible for many instances of suffocation reported in the literature. Thus concerns regarding use of drillholes as an indicator of predation by naticids in modern and fossil deposits should be alleviated. Future work on other alternative modes of predation by naticids, in both laboratory and field experiments, should focus on validating reported occurrences of such predation and identifying different mechanisms that may be involved.

Transcriptional responses of Mytilus chilensis exposed in vivo to saxitoxin (STX)

Abstract: Saxitoxin (STX) is one of the main phycotoxins that contribute to paralytic shellfish poisoning (PSP). This toxin is mainly produced by marine microalgae of the genus Alexandrium. There is evidence of changes at the physiological level in bivalves exposed to STX, although transcriptional responses to STX in bivalves have not yet been studied. The present work evaluates the expression of 13 candidate genes associated with cellular stress and immune response in Mytilus chilensis exposed to STX. Analysis by qPCR showed higher gene transcription levels in M. chilensis injected with STX than in control mussels. High levels of differential gene expression were observed for superoxide dismutase, catalase, ferritin and heat-shock protein genes. To a lesser extent, ependymin, fibrinogen-like, galectin and mytilin B genes were also significantly more expressed in haemocytes of mussels injected with STX that in control mussels. Our results provide insights into how marine toxins could modulate the innate immune system of marine invertebrates.

Pedal surface collecting as an alternative feeding mechanism of the invasive apple snail Pomacea canaliculata (Caenogastropoda: Ampullariidae).

Abstract: Fil: Saveanu, Lucia. Universidad Nacional del Sur. Departamento de Biologia, Bioquimica y Farmacia. Laboratorio de Ecologia; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Bahia Blanca; Argentina

Re-analysis confirms the polyphyly of Lamprotula Simpson, 1900 (Bivalvia: Unionidae)

Abstract: Zhou et al. (2007, Acta Zoologica Sinica, 53: 1024–1030) reported the eastern Asian freshwater mussel genus Lamproula sensu lato Simpson, 1900 (Unionidae) to be polyphyletic and advocated a revision of the genusand family-level classifications. However, their taxon sampling and analyses were insufficient to infer accurately the systematic placement of the resultant clades. We reanalysed their mtDNA ND1 and 16S sequences in a broader phylogenetic context. In addition to nine putative species of Lamprotula s. l., we sampled genera from five of six unionid subfamilies as well as two outgroup families (34 species in total). Both character partitions were analysed separately and in combination under maximum parsimony and maximum likelihood, and combined matrices were also examined using Bayesian inference. Our results confirm support for polyphyly among the species of Lamprotula s. l., with genus-level clades recovered in two different unionid subfamilies. The taxonomic implications of recognizing two genera, Lamprotula sensu stricto (subfamily Gonideinae) and Aculamprotula Wu, Liang, Wang & Ouyang, 1999 (subfamily Unioninae), are discussed, as are anomalies discovered in the published data. It is concluded that, while Lamprotula s. l. is polyphyletic, a more comprehensive revision is necessary to determine the valid names for these two genera.

Rare, divergent Korean Semisulcospira spp. mitochondrial haplotypes have Japanese sister lineages

Abstract: O. Miura1, F. Kohler2,3, T. Lee4, J. Li4 and D. O Foighil4 Oceanography Section, Science Research Center, Kochi University, 200 Monobe, Nankoku, Kochi 783-8502, Japan; Australian Museum, 6 College Street, Sydney, NSW 2010, Australia; Museum fur Naturkunde, Invalidenstr. 43, D-10115 Berlin, Germany; and University of Michigan Museum of Zoology and Department of Ecology & Evolutionary Biology, 1109 Geddes Ave, Ann Arbor, MI 48109-1079, USA

Local adaptation, refugial isolation and secondary contact of alpine populations of the land snail arianta arbustorum

Abstract: Depressed-shelled populations of the land snail Arianta arbustorum occur in rocky Alpine habitats, whereas globular shell forms are ubiquitous in lowland habitats of central Europe. It has been proposed that Alpine, steep, rocky habitats are the ancestral habitat and depressed-shelled snails the ancestral form of A. arbustorum. According to this hypothesis, the globular shell form evolved when A. arbustorum adapted to damp lowland habitats during the Pliocene and depressed-shelled forms survived the Pleistocene glaciations in isolated Alpine habitats like nunataks throughout the Alps. Alternatively, the depressed shells could be a more recent adaptation to steep rocky habitats, derived from the widespread globular-shelled lowland A. arbustorum. To test these alternatives, we compared globular and depressedshelled morphotypes and their molecular differentiation between two geologically similar massifs in the

Progenetic dwarf males in the deep-sea wood-boring genus Xylophaga (Bivalvia: Pholadoidea)

Abstract: Sunken plant debris (sunken wood, hereafter) in deep-sea environments harbours an idiosyncratic fauna that is based directly or indirectly on wood decomposition (Turner, 1973, 1978). This resource is ecologically comparable with deep-sea whale-falls, because of its ephemeral nature (Distel et al., 2000). The obligate wood-boring and wood-consuming (xylophagous) bivalve genera Xylophaga, Xylopholas and Xyloredo, all belonging to the family Xylophagaidae (Turner, 2002; we here regard it as an independent family based on unpublished molecular phylogenetic data of TH), occur primarily in the deep sea, extending down to the hadal zone, from polar to tropical regions (Knudsen, 1961; Schiotte, 2005). They have been recognized as the most important organisms that convert refractory sunken wood into a food source available to other members of the community (Turner, 1973; Distel & Roberts, 1997; Distel, 2003). However, Xylophagaidae remain little studied, as they are difficult to find due to their patchy distribution at great depths. Therefore, many species are known only from the type localities (see Voight, 2007). The reproduction of Xylophagaidae is poorly known so far. Purchon (1941) reported protandric hermaphroditism in Xylophaga dorsalis (Turton, 1819), but this interpretation was recently corrected by Tyler, Young & Dove (2007) to gonochoristic based on a reanalysis of Purchon’s (1941) data. Tyler et al. (2007) also showed gonochorism with a fast growth rate and rapid gametogenesis (in addition to very few examples of simultaneous hermaphroditism) in X. depalmai Turner, 2002. Purchon (1941) and Culliney & Turner (1976) suggested selffertilization for X. dorsalis and X. atlantica Richards, 1942, because both species have paired seminal vesicles (i.e. vesicles in which spermatozoa discharged from the same individual are stored) beneath the pedal retractor in the suprabranchial cavity. Such reproductive patterns have been regarded as a resource adaptation to their deep-sea ephemeral habitats (Purchon, 1941; Culliney & Turner, 1976; Tyler et al., 2007). On the other hand, extended parental care in the form of ‘juvenile brooding’ has often been suggested based on the occurrence of tiny individuals with pediveliger morphologies that are byssally attached to the shell or the soft parts of large Xylophaga individuals (Knudsen, 1961, 1967; Harvey, 1996; Turner, 2002; Voight, 2007, 2008, 2009). However, this proposed developmental mode remained puzzling, because the absence of pelagic larval development implies a low capacity for dispersal and for finding ephemeral resources in the deep sea (Knudsen, 1961; Scheltema, 1994; Voight, 2009). An alternative hypothesis concerning the association of tiny individuals with larger conspecifics in many Xylophaga species is that, instead of externally-brooded offspring, they represent mating partners in the form of dwarf males. Dwarf males are, in general, tiny individuals (50% or less of the normal body size) that attach to large individuals in gonochoristic organisms. They are believed to have evolved among species whose population size is small and/or in which the female is sedentary or hard to find (e.g. Ghiselin, 1974; Vollrath, 1998). The goal of our study was critically to test these two hypotheses by performing a detailed ultrastructural and histological study of tiny conspecifics attached to large individuals of X. supplicata (Taki & Habe, 1950). This species is found in the Western Pacific from Japan to the Philippines at depths of 200–5050 m (Higo, Callomon & Goto, 1999; Haga, 2011). Adults attain a maximum shell length (SL) .15 mm. Xylophaga supplicata can colonize a wide range of submerged wooden substrates, ranging from tree trunks to bamboo branches and even individual mangrove seeds and it exhibits a low population density (T. Haga, unpubl.). Materials examined in this study included the holotype (National Museum of Nature and Science, Tokyo; Mo-39891) in addition to 54 large specimens that had bored into wooden substrates retrieved from waters around Leyte and Bohol, Philippines (n 1⁄4 38) and Espiritu Santo,Vanuatu (n 1⁄4 16). Live animals were carefully removed from the sunken wood by hand, anaesthetized, fixed in 10% seawater-diluted formalin, stored in 70% ethanol, then examined either by freeze-dried scanning electron microscopy (SEM) or by paraffin-embedded serial sectioning. The tiny conspecifics of X. supplicata attach byssally to the surface of the autonomously boring larger conspecifics, either singly or in multiples up to a maximum of 29. There are three areas of attachment: the periostracal extension on the dorsal and ventral side of the posterior slope, and the anterior umbonal area around the mesoplax (Fig. 1; circles). The holotype bears two tiny conspecifics (Fig. 1C); 45 out of the 54 autonomously boring individuals from the West Pacific (83.3%) carried tiny conspecifics. The number of the attached tiny conspecifics increased with host size (R 1⁄4 0.54, P, 0.001), suggesting that

Preference of males for large females causes a partial mating barrier between a large and a small ecotype of littorina fabalis (w. turton, 1825)

Abstract: Species occupying different ecological niches may evolve ecotypes that differ in size as a result of divergent selection on this trait. Size differences may affect mate preference and cause deviations from random mating. Several marine snails of the genus Littorina have ecotypes that differ in size and earlier studies have shown strong assortative mating between differently sized ecotypes in at least one of these species, L. saxatilis. Here we studied male mate choice in two ecotypes of the congeneric L. fabalis that differ in size. We found mating to be nonrandom, because males of the large ecotype followed the mucus trails and copulated with females of their own large ecotype more than with females of the smaller ecotype. Males of the smaller ecotype showed no strong preference, but tended to copulate more with females of the large ecotype than with their own females. Further experiments using the small ecotype showed that mate choice was size-based, with a general preference of the males to mate large females. It seems likely that the partial reproductive barrier that we describe somewhat impedes gene flow between the two ecotypes of L. fabalis, a result that corroborates earlier observations of a weak, but significant, gene-flow barrier across zones where the two ecotypes overlap and hybridize.

Small-scale genetic structure of cerastoderma glaucum in a lagoonal environment: potential significance of habitat discontinuity and unstable population dynamics

Abstract: Environmental heterogeneity in coastal lagoons is expected to facilitate local adaptation in response to different ecological conditions, causing significant genetic structuring within lagoon populations at a small scale and also differentiation between lagoons. However, these patterns and processes of genetic structuring are still poorly understood. The aims of our study were (1) to seek genetic structure at a small scale in Cerastoderma glaucum inside the Mar Menor coastal lagoon using a mitochondrial DNA marker (COI) that has previously detected genetic differentiation inside the lagoon in other species and (2) to evaluate the influence of extreme environmental conditions and habitat discontinuity on its genetic composition. The results indicate high levels of haplotype diversity and low values of nucleotide diversity. COI data provide evidence of significant population differentiation among some localities within the lagoon. Limited gene flow and unstable population dynamics (i.e. fluctuations in population size caused by local extinction and recolonization), probably due to the high environmental heterogeneity, could generate the small-scale genetic divergence detected between populations within the lagoon.

Mating of the slugs Arion lusitanicus auct. non Mabille and A. rufus (L.): Different genitalia and mating behaviours are incomplete barriers to interspecific sperm exchange

Abstract: The large slug known as Arion lusitanicus (or A. vulgaris) is an important pest that is spreading through much of Europe. Arion rufus disappears at sites where A. lusitanicus has established strong populations. The finding of morphological intermediates suggests that A. lusitanicus hybridizes with A. rufus, but interspecific mating had not been proved. Considering the marked differences in their genitalia, it has been hard to envisage how mixed couples might transfer sperm. Arion lusitanicus and A. rufus were collected from pure populations near Gorlitz, Germany, and used for laboratory mating trials involving either two individuals of A. rufus (henceforth RR), two of A. lusitanicus (LL) or one of each species (mixed). Matings were video recorded and some couples were killed during or after copulation to study spermatophore transfer and genital anatomy during mating. Three mixed pairs copulated. However, mixed pairs were significantly less likely to copulate than either RR or LL pairs (7% vs 52 and 36%). At each stage of mating, the probability of proceeding further was lower in mixed pairs than predicted from rates in RR and LL pairs, but this effect was strongest for yin-yang formation and initiating copulation. One problem was that A. lusitanicus tried to circle after yin-yang formation, whereas A. rufus remained stationary. In this respect, and in the repositioning of its everted oviduct, it was A. lusitanicus that compromised. LL copulations lasted over twice as long as RR copulations, but spermatophore formation took similar times, permitting reciprocal spermato- phore exchange in mixed couples even though their copulations ended much earlier than in LL pairs. Our observations of mating behaviour of intraspecific pairs largely agree with previous descrip- tions of A. rufus, but we discuss some discrepancies between our findings and the fuller descriptions available for A. lusitanicus.

Heritability of sperm length and adult shell size in the land snail arianta arbustorum (linnaeus, 1758)

Abstract: Sperm length varies considerably, both between and within species, but the evolutionary implications of this variation are poorly understood. Sexual selection on sperm length requires a significant additive genetic variance, but few studies have actually measured this. Stylommatophoran gastropods have extraordinarily long sperm. However, the extent of intraspecific variation has rarely been examined. Here we present the first estimates of heritability of sperm length in the land snail Arianta arbustorum using two complementary approaches (one-parent –offspring regression and full-sibling split design). We also examined whether sperm length is influenced by the shell size of the snail and estimated heritability of shell size. Sperm delivered by the same individuals in 2–4 matings over two reproductive seasons did not differ in length, indicating a high repeatability of this trait. Offspring of 10 families were kept at three temperatures (11, 15 and 208C) to examine the influence of different environmental conditions on sperm length and adult shell breadth. Independent of shell breadth, sperm length was affected by temperature but not by family of origin (the variance component associated with family was not significantly different from zero), while adult shell breadth was influenced by temperature and family of origin. Higher temperatures resulted in shorter sperm, but larger shells. The heritability of sperm length derived from the two different approaches (one-parent –offspring regression: h 2 + SE ¼ 0.52+ 0.55; full-sibling split design: H 2 + SE ¼ 20.19+ 0.28) suggests relatively little genetic variation in this trait in the studied population. In contrast, the heritability of adult shell breadth indicates a strong genetic effect (mother –offspring regression, h 2 + SE ¼ 0.90+ 0.33). The heritability (h 2 + SE) of adult shell breadth obtained from the father –offspring regression was 0.18+ 0.42, i.e. five times smaller than that of the mother –offspring regression, suggesting a maternal effect on shell size.

Energy metabolism, heart rate and physiological differentiation in the pulmonate gastropod cornu aspersum

Abstract: We explored differences in metabolic rates of the introduced snail Cornu aspersum collected from three distant coastal locations across a 1300 km latitudinal range in Chile and raised under common-garden conditions. We measured two proxies of metabolic rate: heart rate (fH) and CO2 production (standard metabolic rate, SMR) in a flow-through respirometry system. Although both variables were significantly correlated (r 2 ¼ 0.49), suggesting that fH could be a predictor of SMR, the relationship between fH and SMR and also the CO2 pulse (SMR/fH) varied across populations. Whereas SMR suggested an increase in energy metabolism towards high latitudes, supporting metabolic cold adaptation, fH indicated no trend (northern and southern populations exhibited the largest values). Our results suggest that, in invertebrates, energy metabolism cannot be inferred from heart rate. Our results show metabolic differentiation towards increased metabolic heat production in the southern location, warranting further analyses of functional differentiation in these introduced populations.

Small-scale distribution of terrestrial snails: patterns of species richness and abundance related to area

Abstract: Although many studies have dealt with the spatial distribution of land-snail species and individuals, the effect of quadrat size on the interpretation of distributional patterns at small scales has rarely been investigated. We studied the spatial pattern of terrestrial snail distributions within a continuously sampled area of homogeneous habitat at very small scales (, 1m 2 ). The sampling was conducted in two contrasting habitat types: deciduous forests (29 sites) and treeless fens (23 sites) in Central Europe; each site consisted of three nested quadrats (25 25 cm 2 ,5 0 50 cm 2 and 75 75 cm 2 ). On average the forest plots harboured higher numbers of species than fen plots and fen assemblages were composed of significantly smaller species in body volume. Numbers of species and individuals in smaller quadrats estimated from those present in larger ones often deviated significantly from those actually observed, showing frequently aggregated distribution of snails. These deviations were most marked for comparisons involving the smallest quadrats, whereas they almost disappeared in comparisons of large and middle-sized quadrats, both for species and individuals in both habitat types. Proportional deviances between collected and estimated numbers were always significantly higher for individuals than for species, with only one exception. Our results extend previous observations of land-snail spatial aggregations and they raise questions about environmental heterogeneity even in visually homogeneous areas or about possible biotic interactions among individual species. The steeper slope of the regression between area and numbers of species in log-log space from the smallest to the middle quadrat than from the latter to the largest quadrat, and the existence of several cases in which the observed richness was significantly greater than that predicted from rarefaction, suggest that even at this scale there are still idiosyncratic variations in the range of microhabitats available within quadrats.

Antipredatory responses of Perna viridis (Linnaeus, 1758) under acute hypoxia and low salinity

Abstract: The antipredatory responses/attachment behaviour of the green-lipped mussel Perna viridis were studied under combined stresses of hypoxia and low salinity in the presence/absence of its predator, the swimming crab Thalamita danae. There were two oxygen concentrations (1.5 mg l –1 O2 ¼ hypoxic and 6.0 mg l –1 O2 ¼ normoxic) and two salinity levels (15‰ ¼ low, 30‰ ¼ normal). Byssus production performances (including byssal-thread number, byssal-thread diameter, byssal-thread length, cumulative byssal-thread length and volume and frequency of stalk-shedding) were evaluated after 48 h. All variables were significantly affected by dissolved oxygen (DO), salinity and predator presence. Interactive effects of these three factors on byssus production were also observed. Byssus production and frequency of stalk-shedding were lowest in hypoxia low salinity, followed by normoxia low salinity, hypoxia normal salinity, while normoxia normal salinity exhibited the highest values in both predator-presence and non-predator-presence groups. At each treatment of DO and salinity, all parameters in predator-presence groups were significantly higher than in non-predatorpresence groups. Our results indicate that the environmental hypoxia and low salinity impair antipredatory/attachment behaviour and show some synergistic effects. Since reduced byssus production makes the mussels more vulnerable to crab predators, the co-occurrence of hypoxia and low salinity may increase the rates of crab predation on P. viridis in the field.

Molluscan marginalia: hidden morphological diversity at the bivalve shell edge

Abstract: Molluscan shells exhibit a high and largely neglected diversity of serrations and crenulations at the growing margin. A survey of living and Cenozoic fossil bivalves indicates that serrations, in which the external ribs or interspaces between ribs extend radially beyond the general contour of the valve margin, may be symmetrical or asymmetrical. Projections whose adumbonal edge more nearly parallels the shell edge than the abumbonal edge occur on the posterior valve margins of many limids, cardiids and donacids, as well as in the arcid Anadara and a few concentrically ridged tellinids. In many cardiids, posterior serrations form as extensions of ribs, whereas ventral and anterior projections are extensions of rib interspaces. Asymmetrical serrations are almost always found on shell edges that are polished, indicating that the mantle extends slightly over the valve margin to the outside. I tentatively suggest that asymmetrical serrations enable the valves to close around siphons or other mantle extensions without injuring these soft tissues, so that the bivalve can maintain sensory contact with the environment even while the shell is shut. A preliminary comparison with brachiopods indicates that the diversity of conditions at the shell edge is much higher in bivalves. Together with the largely warm-water and marine distribution of marginal modifications in bivalves, these comparisons reflect the higher metabolic potentials of bivalves relative to brachiopods, and show that the shell edge is a rich source of evidence about function and mode of life in fossils.

Bacterial symbiosis in syssitomya pourtalesiana oliver, 2012 (galeommatoidea: montacutidae), a bivalve commensal with the deep-sea echinoid pourtalesia

Abstract: For the first time, bacterial symbiosis is recognized in the bivalve family Montacutidae of the superfamily Galeommatoidea. The ctenidial filaments of Syssitomya pourtalesiana Oliver, 2012 are extended abfrontally and a dense layer of bacteriocyte cells cover the entire surface behind a narrow ciliated frontal zone. The bacteria are extracellular and held within a matrix of epithelial extensions and microvilli. There is no cuticular layer (glycocalyx) covering the bacteria as in many thyasirid symbioses. The bacteriocytes hold more than one morphotype of bacteria, but bacilli, 1– 3 mm in length, dominate. Scanning electron microscopy observations show a surface mat of filamentous bacteria over the extreme abfrontal surfaces. Filter feeding was confirmed by the presence of food particles in the stomach and the bivalve is presumed to be mixotrophic. Syssitomya is commensal and lives attached to the anal spines of the deep-sea echinoid Pourtalesia. In this position, echinoid feeding currents and echinoid faecal material may supply the bacteria with a variety of nutrient materials including dissolved organic matter.

Intragenomic sequence variation at the its1–its2 region and at the 18s and 28s nuclear ribosomal dna genes of the new zealand mud snail, potamopyrgus antipodarum (hydrobiidae: mollusca)

Abstract: Molecular genetic analysis was conducted on two populations of the invasive non-native New Zealand mud snail (Potamopyrgus antipodarum), one from a freshwater ecosystem in Devil’s Lake (Oregon, USA) and the other from an ecosystem of higher salinity in the Columbia River estuary (Hammond Harbor, Oregon, USA). To elucidate potential genetic differences between the two populations, three segments of nuclear ribosomal DNA (rDNA), the ITS1-ITS2 regions and the 18S and 28S rDNA genes were cloned and sequenced. Variant sequences within each individual were found in all three rDNA segments. Folding models were utilized for secondary structure analysis and results indicated that there were many sequences which contained structure-altering polymorphisms, which suggests they could be nonfunctional pseudogenes. In addition, analysis of molecular variance (AMOVA) was used for hierarchical analysis of genetic variance to estimate variation within and among populations and within individuals. AMOVA revealed significant variation in the ITS region between the populations and among clones within individuals, while in the 5.8S rDNA significant variation was revealed among individuals within the two populations. High levels of intragenomic variation were found in the ITS regions, which are known to be highly variable in many organisms. More interestingly, intragenomic variation was also found in the 18S and 28S rDNA, which has rarely been observed in animals and is so far unreported in Mollusca. We postulate that in these P. antipodarum populations the effects of concerted evolution are diminished due to the fact that not all of the rDNA genes in their polyploid genome should be essential for sustaining cellular function. This could lead to a lessening of selection pressures, allowing mutations to accumulate in some copies, changing them into variant sequences.

Mating behaviour and general spawning patterns of the southern dumpling squid Euprymna tasmanica (Sepiolidae): a laboratory study

Abstract: We provide the first detailed description of mating behaviour and multiple mating in the southern dumpling squid, Euprymna tasmanica (Pfeffer, 1884) in the laboratory, as well as details on their general spawning patterns. We found that male E. tasmanica increase the number of ‘pumps’ (mantle contractions) when mating with females that had recently mated, showing that males are able to determine the recent mating history of females. We also found that at the conclusion of mating, the male’s hectocotylus was enlarged. To our knowledge, neither had previously been described in sepiolid squid. Euprymna tasmanica females lay multiple clutches over a large proportion of their lifespan, from 1 to 121 d. There was a considerable variation in the number of eggs produced per female in captivity, ranging from 6 to 646 eggs, and in the number of eggs per clutch, from 6 to 163 eggs. Egg number per clutch declined significantly over the spawning period. Larger females produced larger hatchlings, and egg mass and hatchling mass were significantly correlated. At higher ambient water temperatures the rate at which females produced clutches increased and the size of the eggs laid decreased.

A molecular phylogenetic framework for the Ergalataxinae (Neogastropoda: Muricidae)

Abstract: The validity of the muricid subfamily Ergalataxinae has recently been confirmed with molecular data, but its composition and the relationships among its constituent genera remain unclear. In order to investigate this, we use four genes (28S rRNA, 12S rRNA, 16S rRNA and cytochrome c oxidase subunit I) to construct a Bayesian phylogeny of 52 ergalataxine species in 18 genera, representing c. 40% of the currently accepted species and 86% of the genera. This is the most complete phylogeny of this taxonomically confusing subfamily yet produced. Our results indicate the polyphyly of many traditional genera, including Morula, Pascula and Orania. In order to improve the correspondence between classification and phylogeny, we restrict the definition of Morula, resurrect Tenguella and elevate Oppomorus to full genus, but describe no new genera. Several species in this analysis could not be identified and may be new, but we do not describe them. Further molecular and morphological analyses, in the context of this framework, should help to resolve the remaining ambiguities in the classification of this subfamily. The oldest fossil member of the Ergalataxinae known to us is of Early Oligocene age.

Spatial and temporal dynamics of Corbicula fluminea (Muller, 1774) in relation to environmental variables in the Mondego Estuary (Portugal)

Abstract: From 2003 to 2008, research on spatial and temporal dynamics of Corbicula fluminea was conducted at 10 sites along the Mondego Estuary (Portugal). A clear spatial and temporal variation in terms of density and biomass was observed, the highest values being found in the upstream oligohaline site, especially in warmer seasons. Seasonal density ranged from 4 to 11 500 individuals m 22 . Biomass ranged from 0.01 to 323 g ash-free dry weight m 22 . Comparing the results collected in the Mondego Estuary with other European and American invaded ecosystems, the density values are extremely high, but the biomass is lower than some of the reported values. This can be explained by the dominance of very small animals in the Mondego Estuary. Furthermore, the stepwise multiple regression model combining environmental variables and biomass of C. fluminea predicted that the areas with higher values of temperature and phosphate, together with lower values of salinity, water flow and silt and clay, support higher biomass. In 2005, a large reduction in density was recorded and was related to the massive mortality of small individuals as a consequence of the severe drought that occurred in the Mondego Estuary.

Driftwood as a vector for the oceanic dispersal of estuarine gastropods (Neritidae) and an evolutionary pathway to the sunken-wood community

Abstract: Yasunori Kano1, Hiroaki Fukumori1,2, Bastian Brenzinger3 and Anders Waren4 Department of Marine Ecosystems Dynamics, Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan; Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan; Bavarian State Collection of Zoology, Munchhausenstr. 21, D-81247 Munich, Germany; and Swedish Museum of Natural History, Box 50007, SE-10405 Stockholm, Sweden

First case of possible iteroparity among coleoid cephalopods: the giant warty squid Kondakovia longimana

Abstract: Modern teleost fish and coleoid cephalopods (squid, cuttlefish and octopods) share the same ecological niche as meso-and macronektonic predators of the World Ocean. In spite of convergence of their lifestyles (Packard, 1972), some important differences exist between these taxa, one being their respective reproductive patterns, particularly semelparity vs iteroparity. Following Rocha, Guerra, & Gonzalez (2001) who refined the original definition of iteroparity (Cole, 1954), we use the term iteroparous for species that “spawn once a year, survive, feed, grow and regenerate their gonads for a further reproductive event the following year” (Rocha et al. 2001: 292). Animals that have short lifespans are automatically eliminated from this category regardless of their spawning pattern. This definition restricts the possibility of iteroparity to those few cephalopods that live for many years. The vast majority of fish are iteroparous and reproduce several times during their lives; semelparous reproduction, as in Pacific salmon, is a rare phenomenon among them. In contrast, the only cephalopods known to breed over several seasons are ectocochleate species of Nautilus. All known endocochleate coleoid cephalopods are semelparous: they reproduce just once and their gonad never returns to an immature condition between spawning events (Rocha et al., 2001), as it does in iteroparous fishes (Wallace & Selman, 1981). The capture of a large female of the giant warty squid Kondakovia longimana Filippova, 1972 (Oegopsida: Onychoteuthidae) questions this established point of view. Endemic to the Antarctic epiand mesopelagic water masses, this squid also occurs near-bottom, attaining 1,100 mm mantle length (ML) (more than 2 m total length and ca. 30 kg in body weight) and living between 4 and 10 years (Bizikov 1991; Jarre, Clarke, & Pauly, 1991; Vacchi, Greco, & La Mesa, 1994; Lynnes & Rodhouse, 2002). Adult Kondakovia are an important prey of sperm whales and elephant seals, and juveniles are preyed upon by albatrosses and penguins (Collins & Rodhouse, 2006). Nothing is known about reproduction of this species. An adult female of this species was captured by the longliner Argos Froyanes on 15 February 2012 in the Ross Sea at 708240S, 1228420W at 1,700 m depth (Fig. 1) and was brought frozen to Stanley, Falkland Islands. Dorsal mantle length was 890 mm (measured frozen) and total weight was 18.1 kg. Its extended oviducts were simple elongated tubes, relatively larger than those of a mature Onykia ingens (Laptikhovsky, Arkhipkin, & Hoving, 2007), with no meandering as is seen in such batch spawners as the squid families Ommastrephidae and Loliginidae. Their walls were relatively flabby. The proximal oviducts held 12 ripe ovulated eggs, measuring 4.0 2.5 mm. The ovary of the Kondakovia (Fig. 2) did not contain postovulatory follicles (POF). The ovary itself was in good condition and contained some 2,522,532+ 355,419 protoplasmic oocytes of about 0.5 mm modal length (Fig. 2). The nidamental glands were 317 mm long (35.6% ML), similar to those in mature female O. ingens (32.3–58.9%, mean 42.8% ML; A. Arkhipkin & V. Laptikhovsky, unpublished) and much larger than in immature K. longimana (9.8–14.0%; Filippova, 1972). The oviductal glands were also much enlarged, similar to those of maturing squids of O. ingens. The stomach contained some fish scales. Inspection of inner and outer body surfaces, on which spermatophores are normally attached in this family (Hoving & Laptikhovsky, 2007; Bolstad & Hoving, 2011), as well as of the arms, buccal membrane and other possible sites of spermatophore attachment, revealed no trace of spermatangia. There was no evidence of body degeneration and in every respect this appeared to be a healthy active squid, despite the 12 ripe eggs in the proximal oviduct. What evidence indicates this species has an iteroparous life history? First, spent representatives of the family Onychoteuthidae are typified, in for example the squid genus Onychoteuthis, by a thin and flaccid mantle with its relative proportions as well as those of fins greatly distorted. This can occur to such a degree that post-spawning animals were described as different genus and species “Chaunoteuthis mollis Appellof, 1891” (Arkhipkin & Nigmatullin, 1997). Similar processes of mantle degeneration are known in other onychoteuthid genera such as Onykia, Notonykia and Callimachus (Bolstad & Hoving, 2011). Second, if the 12 eggs found in oviducts were just a small part of the portion that had previously been spawned, we might suppose that POF were already resorbed—an indication that spawning happened some time ago. In Antarctic fish POF atresia can take up to 5–7 months (Everson, 1970; Butskaya & Faleeva, 1987; La Mesa, Caputo & Eastman, 2007). Third, the walls of the oviducts were relatively flabby, not straight and rigid as might be expected in immature or early maturing squid that had never held mature eggs, supporting the supposition that this animal had spawned before.

3D reconstruction of the anatomy of the ovoviviparous (?) freshwater gastropod Borysthenia naticina (Menke, 1845) (Ectobranchia: Valvatidae)

Abstract: Because of its apertural shape and an unusual reproductive mode, Borysthenia naticina (Menke, 1845) has always held a special position within the Valvatidae. The species is known to be viviparous, whereas all other valvatids produce spawn. Living animals from the Bavarian Danube river provided the opportunity to investigate the structure of the genital system in relation to this special mode of reproduction. We applied 3D surface- and volume-rendering techniques using AMIRA ® , based on histological semithin slices. We also provide SEM photos of the taenioglossate radula of this species. Contrary to our expectations, there were no special structures (e.g. brood pouch) in the genital system that could be connected with such an accelerated early ontogeny. In general, only minor anatomical differences were found between Borysthenia naticina and other valvatid species. The previous reports of ovoviviparity need at least to be modified, because true spawn was observed, although the embryos were close to hatching. The generally accepted taxonomic status of Borysthenia as a genus distinct from Valvata is doubtful, and the family Valvatidae is in need of a thorough systematic revision.

New insights on stomach anatomy of carnivorous bivalves

Abstract: Carnivory is unusual among bivalve molluscs and is limited to a few families in the distantly related orders Pectinida, Mytilida and Anomalodesmata. Despite the significance of dietary shifts in the evolution of the bivalves, the anatomy of the alimentary system, and of the gastric chamber in particular, has been described in detail for only a few carnivorous species. Here we describe the anatomy of the gastric chamber in a pectinid, Propeamussium jeffreysii, and an anomalodesmatan, Bathyneaera demistriata, expanding the known morphological disparity of the alimentary system in both groups. We found the stomachs of both to be modified to varying degrees for a carnivorous habit, with thickened, muscular walls, extensive cuticular linings, and reduced sorting areas and gastric chamber compartments (i.e. the dorsal hood, the left pouch and the food-sorting caecum). Despite some superficial similarity, each retains distinct hallmarks of their ancestry among filter-feeding relatives, allowing precise homology assessment of individual characters to differentiate between them. In addition, we found that the gastric chamber of P. jeffreysii represents an intermediate morphology between previously described P. lucidum and filter-feeding pectinids. Consequently, variation in the anatomy of the gastric chamber in Pectinida parallels a previously identified trend towards greater specialization for carnivory in the Anomalodesmata. Our results indicate that the current classification scheme of stomach types does not reflect phylogenetic affinity across the Bivalvia and highlight the need for accurate homology assessment of individual characters of the gastric chamber for inferring evolutionary relationships.

Reproductive organogenesis in the apple snail Pomacea canaliculata (Lamarck, 1822), with reference to the effects of xenobiotics

Abstract: The complex array of male and female reproductive organs in Pomacea canaliculata develops from the gonoductal and copulatory primordia. These primordia are present in both sexes, but while the gonoductal primordium (or ‘gonoduct’) is present in hatchlings, the copulatory primordium only appears in juveniles at the 5-mm (shell length) stage. The proximal portion of the gonoduct will produce the gonad, while the more distal portions will produce the accessory sexual organs (the visceral vas deferens, pallial seminal vesicle, prostate and genital papilla in males, and the visceral oviduct, uterus and vagina in females). The gonadal portion of the gonoduct differentiates histologically into either the testis or the ovary at the 10-mm stage, while the more distal portions remain undifferentiated and the copulatory primordium remains approximately the same size in both sexes. The copulatory rudiment becomes larger in juvenile males at the 15-mm stage and rudiments of all adult components have appeared by then. At this stage, the pallial gonoduct differentiates into either the pallial seminal vesicle and prostate, or the uterus and vagina. Subadults at the 20-mm stage possess either some mature spermatogenic nests or some large oocytes. Crossing of the genital papilla over the rectum, a crucial event in male differentiation, has already occurred at this stage. Sexual differentiation of the operculum and the initiation of copulatory behaviour occur between the 15- and 20-mm stages, while oviposition begins c. 2 weeks later. Full development of gonoduct derivatives is reached at the 25-mm stage in both sexes. However, the copulatory structures remain rudimentary in females, even though they may still develop to some extent later on. These findings not only indicate two distinct origins of reproductive organs, but also several developmental stages during which different control mechanisms may operate. This has implications for understanding potential targets and responses to endocrine-disrupting xenobiotics.

Studies on the morphology and growth of statoliths in Caenogastropoda

Abstract: Gravireception in gastropods occurs by the displacement of statoparticles (multiple statoconia or a single statolith) inside statocysts, resulting from changes in the animal’s position. An easy method for extraction and processing of statoliths is given and their morphology and microstructure described in 12 species of caenogastropods collected on the NW Portuguese coast, belonging to eight different families. In addition, statolith growth was studied in two species, Nucella lapillus and Nassarius reticulatus. The relation between statolith diameter (StD) and shell height (SH) follows logistic curves [in N. lapillus SH ¼ 34.98/(1 þ 190.817 249.082 StD ), P , 0.001; and in N. reticulatus SH ¼ 31.03/(1 þ 116.709 236.577 StD ), P , 0.001]. All statoliths observed are hard and translucent, with several concentric layers delimited by well-marked growth rings. Recently, some studies have shown that these rings are annual and can be used to determine the age of some gastropods and we show that this applies in a wider range of caenogastropods. Statolith rings were clearer in species collected offshore (Aporrhais pespelecani, Ranella olearium, Charonia lampas and N. reticulatus), because additional disturbance rings were more often present in statoliths from inshore species (Crepidula fornicata, Littorina littorea, Peringia ulvae, Trivia monacha, N. reticulatus, Nassarius incrassatus, N. lapillus, Ocenebra erinaceus and Ocinebrina aciculata). Statoliths thus have potential for sclerochronology and may provide an important record of the physical and chemical characteristics of the marine environment throughout ontogeny.

High-speed camera observations of copulatory behaviour in Idiosepius paradoxus: function of the dimorphic hectocotyli

Abstract: Right © The Author 2013. Published by Oxford University Press on behalf of The Malacological Society of London.; This is a pre-copy-editing, authorproduced PDF of an article accepted for publication in Journal of Molluscan Studies following peer review. The definitive publisherauthenticated version Journal of Molluscan Studies, 79(2), pp.183-186; 2013 is available online at: http://dx.doi.org/10.1093/mollus/eyt005 NAOSITE: Nagasaki University's Academic Output SITE