Showing papers in "Journal of Molluscan Studies in 2010"

Behavioural adaptations of mussels to varying levels of food availability and predation risk

Abstract: Blue mussels Mytilus edulis (n ¼ 14) were studied in the laboratory using Hall sensor systems to record their gaping behaviour when exposed to varying food rations and levels of predation risk. Mussel response to increasing daily algal ration was to increase mean gape angle per day and was associated with copious pseudofaeces production at excessive initial algal concentrations, e.g. 250 cells/ml. Mean gape angle decreased (backward S-shaped curve) when fed a fixed algal ration per day where simulated predation risk (introduced fresh mussel homogenate) increased in the water, presumably as an anti-predation strategy. However, this behaviour is presumed to lower feeding rates. There was a general positive relationship between both gape angle and the extent of valve movement (abduction/ adduction) per event and valve movement speed. However, the fastest valve adduction events, which resulted in valve closure, were recorded independent of gape angle and only when mussels were first exposed to high perceived predation risk. We interpret this as an appropriate response, with high energetic cost, as a first line of defence from predators such as starfish and crabs. Overall, mussel response to predation appears graded and complex, indicating a trade-off between maximizing feeding/pseudofaeces production and minimizing predation risk.

Feeding rates of an introduced freshwater gastropod pomacea insularum on native and nonindigenous aquatic plants in florida

Abstract: Pomacea insularum (Gastropoda: Ampullariidae) is a common, nonindigenous species in many parts of the world and an important consumer of aquatic macrophytes We conducted laboratory trials to quantify the rates of consumption of native and nonindigenous aquatic plants in Florida, where this snail has been introduced Twenty-two freshwater plant and alga species were presented to naive P insularum in laboratory trials, using single-snail replicates and simultaneous (no-snail) controls Pomacea insularum damaged 50% of the replicate plants of 16 species; for 14 of these we calculated ash-free dry weight-specific feeding rates of P insularum The most heavily consumed plants were two native species: Limnobium spongia (0744 g/g/d) and Chara sp (0478 g/g/d) Nonindigenous Panicum repens (0306 g/g/d), Hydrilla verticillata (0292 g/g/d) and Ceratophyllum demersum (0254 g/g/d); and native Sagittaria latifolia (0257 g/g/d), Najas guadalupensis (0225 g/g/d) and Vallisneria americana (0207 g/g/d) were also heavily consumed Nonindigenous Eichhornia crassipes was consumed at a lower rate (0053 g/g/d) while nonindigenous Colocasia esculenta and Pistia stratiotes were not consumed at detectable levels Our results suggest that P insularum cannot be relied upon as a biological control agent for nonindigenous plants and may heavily impact native macrophytes

Abyssogena: a new genus of the family Vesicomyidae (Bivalvia) from deep-water vents and seeps

Abstract: A new genus Abyssogena is established for A. phaseoliformis (Metivier, Okutani & Ohta, 1986) and A. kaikoi (Okutani & Metivier, 1986), which were previously assigned to the genus Calyptogena Dall, 1891, and also for two new species, A. southwardae and A. novacula. The most characteristic features of Abyssogena are an elongate shell up to about 280 mm in length; a pallial line starting from the ventral margin of the anterior adductor scar; secondary pallial attachment scars developed dorsal to the pallial line; radially arranged hinge teeth with a reduced anterior cardinal tooth in the right valve; and presence of an inner ctenidial demibranch only. Abyssogena occurs in deep water from 2,985 to 6,400 m and is distributed in the Pacific and Atlantic Oceans at cold seeps along continental margins and hydrothermal vents at mid-oceanic ridges. Some species have a remarkably wide geographic dis- tribution; A. southwardae is present throughout the Atlantic and A. phaseoliformis is present in Japan, Kuril-Kamchatka, as well as Aleutian Trenches. No fossils of Abyssogena are known.

Snail faunas in the Southern Ural forests and their relations to vegetation: an analogue of the Early Holocene assemblages of Central Europe?

Abstract: A malacological study at 41 forest sites in the Southern Urals (Bashkortostan, Russia) conducted in 2007 gave the first quantitative data about land snail assemblages from this region. We explore the hypothesis that forests of this area are modern analogues of the Early Holocene forests of Central Europe. Snail species significantly accumulated towards more fertile, calcium-rich, and lowland sites; the richest faunas were in alluvial alder forests and mesic lime-maple-elm forests. Several features such as low snail species richness, predominance of generalist species with wide distributions, and broader realized niches of particular species in the Southern Ural forests relative to their niches elsewhere, corresponded to those of fossil assemblages from the Early Holocene deposits of Central Europe. Our data also suggest that the very limited species pool, results in species poor assemblages which are structured mainly by environmental filtering.

Modelling population density of Pinna nobilis (Bivalvia) on the eastern and southeastern coast of Tunisia

Abstract: The distribution and density of Pinna nobilis was assessed along the eastern and southeastern coasts of Tunisia, based on line-transect data collected by SCUBA diving. An information-theory approach was followed for inference, and generalized additive models were fitted to model the population density of fan mussels using environmental and spatial covariates. The density of fan mussels was significantly correlated with depth and the distance from the city of Gabes. The fan mussel density was practically zero in very shallow water (,0.3 m depth) and increased with depth within the depth range of this study (0– 6 m). The species was observed within Posidonia oceanica, Cymodocea nodosa and Caulerpa prolifera beds, with no evident difference in density among habitats. Zero fan mussel densities were observed near the city of Gabes. Population density increased with the distance from Gabes and was higher in the south than in the north. This decline of P. nobilis density near Gabes could be an effect of marine pollution due to the dumping of large quantities of phosphogypsum and other chemical products and the associated degradation of the benthic habitats in the area during recent decades.

Ecrobia grimmi in brackish Lake Sawa, Iraq: indirect evidence for long-distance dispersal of hydrobiid gastropods (Caenogastropoda: Rissooidea) by birds

Abstract: Mudsnail species of the genera Hydrobia and Ecrobia ( junior synonym Ventrosia) belong to morphostatic or nonadaptive radiations. Although these genera are anatomically well defined, their species can only be confidently identified using molecular data. During the last decade, the status, distribution and evolutionary history of these coastal, brackish water taxa have been clarified in large part. In general, congeneric (sub)species have nonoverlapping ranges replacing each other ecologically on large geographical scales (Wilke & Davis, 2000; Wilke, Rolan & Davis, 2000; Wilke & Pfenninger, 2002; Wilke, Pfenninger & Davis, 2002; Wilke, 2003; Kevrekidis, Wilke & Mogias, 2005). However, the discovery of isolated inland populations of these snails, such as an Ecrobia in Lake Sawa in Iraq, does not fit into this picture. Lake Sawa, which is located in the southwestern part of Iraq, is a mixomesohaline water body. It has a maximum depth of 5.5 m and no surficial influx or outflow. The lake is fed by groundwaters of the Euphrates and Dammam aquifers and its water chemistry, which is unique among Iraqi lakes, suggests that it is probably of relatively recent karstic origin and not a relic of a mid-Holocene marine incursion (Jamil, 1977; Naqash, Banat & Al-Shamee, 1977; Plaziat & Younis, 2005; Hassan, Al-Saadi & Alkam, 2006). The distances between Lake Sawa and the nearest populations of brackish-coastal hydrobiids are over 800 km to the Caspian Sea and over 900 km to the Mediterranean (Fig. 1). The purpose of this note is to identify the hydrobiid snail that lives in Lake Sawa and to infer its origin based on molecular analyses. We also discuss, within this context, the importance of birds as vectors for the dispersal of coastal hydrobiid gastropods, which has been contested (e.g. Barnes, 1988). Snails in Lake Sawa were collected by hand or washed from stones and fixed in ca 85% ethanol. Dissections indicated that they belonged to the genus Ecrobia. In order to identify the species we sequenced a 638-bp fragment of the cytochrome c oxidase subunit I gene (COI) of three specimens and compared it with that of congeners whose sequences were extracted from GenBank (for E. ventrosa we selected five individuals spread across its entire geographic range) as well as to unpublished sequences from our ongoing phylogenetic studies. Hydrobia acuta acuta, Peringia ulvae and Salenthydrobia ferreri served as outgroups (Table 1). DNA preparation and PCR followed standard procedures (Wilke et al., 2006; Haase, 2008). For sequencing, PCR products were sent to AGOWA (www.agowa .de). Base composition was homogeneous, a prerequisite for model-based phylogenetic analyses. Phylogenetic analyses were conducted based on the optimality criteria maximum parsimony (MP) and maximum likelihood (ML) as well as by neighbour-joining (NJ) and Bayesian inference (BI). Optimal substitution models (HKY þ G) were inferred using jModeltest v. 0.1 (Posada, 2008) and MrModeltest v. 2.3 (Nylander, 2004), respectively. Trees were reconstructed in PAUP* v. 4b10 (Swofford, 2003) and MrBayes v. 3.1.2 (Ronquist & Huelsenbeck, 2003). For MP and ML, starting trees were obtained via stepwise addition. The addition sequence was random and random trees were used as starting points. Tree search went through 10,000 replicates, each limited to 10 rearrangements, which were done by TBR-branch swapping. Bootstrapping was performed with 10,000 (MP, NJ) and 1,000 (ML) replicates, respectively. For BI, four Metropolis-coupled Markov chains each searching the tree space in two parallel runs were sampled every 100th generation of a total of 2,000,000. The burn-in was conservatively set to 500,000 generations. At this point, the standard deviation of split frequencies had already dropped below 0.01, suggesting that both searches were already sampling around the same optimum. Convergence of parameters was monitored using Tracer v. 1.4 (A. Rambaut & A. Drummond, http://tree.bio .ed.ac.uk/software/tracer/) as well as the criteria implemented in MrBayes. The three specimens from Lake Sawa had identical sequences. They differed from the Caspian sequence of E. grimmi in only three positions and therefore are most likely conspecific. However, assigning a specific name can only be done tentatively in this case owing to the large number of nominal hydrobiid taxa that were described from the Caspian and Aral Seas by Starobogatov and co-workers (see Filipov & Riedel, 2009, and references cited therein). Filipov & Riedel (2009) suggested that only a single species is involved, with the oldest available name for this snail being Hydrobia grimmi Clessin & Dybowski, 1888. Hence, we tentatively assign the hydrobiid snail that lives in the Caspian Sea and Lake Sawa to this species, pending detailed taxonomic study of the hydrobiid taxa of the Ponto-Caspian region. The tree reconstructions are summarized in Figure 2 based on the ML topology, which had the highest resolution. The closest relative of E. grimmi was, as expected based on distributional evidence, E. maritima, which lives in the Black Sea and adjacent Mediterranean (Kevrekidis et al., 2005). Surprisingly, the sister species of this clade was E. truncata, a Western Atlantic species. Ecrobia ventrosa, which is widely distributed in the Mediterranean and northeast Atlantic (Wilke & Davis, 2000), was sister to the above species. An unnamed species from the Tunisian island of Djerba branched off at the base of the tree; this will be dealt with in a comprehensive phylogeographic analysis of the entire genus that is in progress. The support values of the four tree-reconstruction methods were very heterogeneous (Fig. 2). Posterior probabilities usually are expected to be higher than bootstrap values. However, this was only the case in two of the seven nodes supporting the species and their relationships. Two nodes were Correspondence: M. Haase; e-mail: martin.haase@uni-greifswald.de

Cryptic species in Gemmuloborsonia (Gastropoda: Conoidea)

Abstract: During a broad molecular taxonomic and phylogenetic survey of the gastropod superfamily Conoidea, 80 specimens of several species of the genus Gemmuloborsonia were sequenced for the cytochrome c oxidase subunit I gene. The genus, originally established for fossil species from the Plio-Pleistocene of the Philippines, now includes living species from bathyal depths of the Indo-Pacific Oceans. The molecular data demonstrated the presence of five separate entities, while only four ‘morphospecies’ could be isolated by visual examination. The two largest groups, representing separate species from the molecular data, were impossible to distinguish with certainty using shell or anatomical characters. To examine shell morphology in more detail the shape of the last whorl was analysed by Fourier analysis, and the Fourier coordinates were used in canonical variate analysis. The majority of the specimens were separated into two groups, but 21.6% of the specimens were impossible to distinguish by morphological characters. One of these two forms was attributed to the known species Gemmuloborsonia moosai Sysoev & Bouchet, 1996, while the other is described as a new species Gemmuloborsonia clandestina. Bathytoma colorata Sysoev & Bouchet, 2001 is transferred to Gemmuloborsonia on the basis of molecular analysis and radular morphology. Another species, represented in our material by a single specimen, remains undescribed.

Reproductive seasonality, oviposition and development of the nassariid whelk Buccinanops cochlidium (Dillwyn, 1817) in Patagonia, Argentina

Abstract: Seasonality of reproduction in Buccinanops cochlidium, including mating, oviposition and embryonic development, was studied within a population in Patagonia. Mating was observed mainly during autumn and winter (March to October). Females carrying egg capsules were found between July and October when water temperature was 108C, while development of embryos continued until February (the hatching peak) when water temperature was 188C. All egg capsule masses were found attached to the shells of females 80–102 mm in length. The spawn consisted of 80 to 238 egg capsules, attached to the apertural callus of the shell. Linear regression analysis showed no significant relationship between female size and number of egg capsules. Each egg capsule contained 3100 eggs on average, with a mean egg diameter before cleavage of 227.5 mm. One to 20 embryos completed their development within each egg capsule by ingesting around 570 nurse eggs. The embryos followed a typical holoblastic spiralian division until gastrulation. During the ‘veliger’ stage the embryo consumed nurse eggs and formed a large rounded embryo up to 2 mm in diameter. After shell development the embryos hatched as crawling juveniles of 4.0 mm shell length through an opening opposite to the capsule stalk. There was an inverse relationship between the mean hatching shell size and the number of embryos per egg capsule. Under laboratory conditions development was completed in four months.

Acidophilic terrestrial gastropod communities of north america

Abstract: Habitats with soil pH , 4 and Ca , 100 ppm, such as pocosins, Sphagnum bogs and heathlands, would appear inimical to land-snail biodiversity. Nevertheless, a survey of 1,356 sites, c. 1/2 million individuals and over 240 species (c. 1/5 of the continental fauna) across North America shows that c. 10% of species appear to favour such highly or moderately acidic sites, spread from subtropical forests of the Gulf of Mexico coast to the arctic tundra. Nonmetric multidimensional scaling ordination of faunas from 292 sites that support at least five co-occurring species documents that the principal axis of compositional variation in highly and moderately acidic habitats is significantly (P , 0.0005) correlated with latitude, while the second axis is significantly (P , 0.0005) correlated with moisture level. Composition was found to vary continuously along both axes, implying that discrete acidophilic communities are not present. While highly and moderately acidic sites were shown to have significantly (P , 0.000000005) lower richness and abundance compared with neutral/calcareous habitats, even the most acidic sites still typically supported 5–10 species. Abundance distributions in highly acidic habitats were found to be more uneven those of neutral/calcareous sites. The greater richness of the North American acidophilic land snail fauna compared with that in Europe has allowed communities to display replacement-driven compositional turnover. These results demonstrate that it is vitally important for biodiversity surveys of North American land snails not to ignore acidic habitats, because they harbour an important and surprisingly diverse fauna.

Needles and pins: acicular crystalline periostracal calcification in venerid bivalves (Bivalvia: Veneridae)

Abstract: A scanning electron microscope study of the periostracum of 50 species of venerid bivalves revealed that periostracal calcification in the form of aragonitic needles and shorter pins is widespread within the family. Together with organic and sediment coatings that are found in some species, these needles form an integral part of the functional shell. Visible as a white ‘crust’ on the outside of shells, long slender needles (up to 400 mm long and 1 mm wide) without adherent material are seen in species of Tivela and Lioconcha and in Gomphina undulosa. Other venerids including Pitar species, Mysia undata and Compsomyax subdiaphana have short pins, capped with a fibrous organic matrix and significant coatings of sediment. Callocardia hungerfordi and Clementia papyracea have very thick sediment coatings underlain by short pins, while Gafrarium and Circe species have short pins with a thin, robust, organic coating and little particulate material. Finally, there are species, including Venus verrucosa, Chione elevata and Mercenaria mercenaria, where minute, ,1 mm long pins also underpin a thin organic coating. Details of formation were studied in Tivela lamyi and Lioconcha ornata, where the needles are elongate hexagonal crystals of aragonite enveloped by an organic sheath, which grow at their proximal ends from within the periostracum, connected to the outer mantle epithelium via narrow channels. Growth of needles ceases following the onset of shell calcification. The distribution of the periostracal structures was examined in relation to a published molecular phylogeny that recognized two major clades within the family. Larger needles and pins are confined to the clade that includes subfamilies Pitarinae, Gouldinae, Meretricinae and Petricolinae, while submicron-sized pins are found only in the Venerinae and Chioninae of the second clade. Calcified periostracal structures appear to be absent in Tapetinae and Dosiniinae.

Phylogenetic analysis of Dendronotus nudibranchs with emphasis on northeastern Pacific species

Abstract: Molecular and morphological evidence suggests that the taxonomic status of several eastern Pacific species of Dendronotus needs a reassessment. Dendronotus diversicolor and D. albus are synonymized due to lack of genetic variation in the 16S rRNA gene and of any significant morphological differences. Dendronotus nanus and D. iris are also regarded as synonyms based on a reevaluation of ecological and morphological data. Finally, the name D. venustus is resurrected for eastern Pacific populations previously considered to be D. frondosus. Pacific D. venustus display consistent morphological and molecular differences from Atlantic D. frondosus. The molecular phylogeny presented here is not robust enough to shed light on the evolution and biogeography of Dendronotus, but preliminary evidence indicates that the Pacific species of Dendronotus are not a monophyletic group, because Arctic and Atlantic species are nested within them. The 16S rRNA genetic diversity within Dendronotus is very small compared to that of other related groups. These data, along with the comparatively large diversity of Dendronotus in the Pacific, suggest the possibility that relatively recent Arctic migration and vicariance along Beringia may have been involved in the evolution of this group.

Predation on hardest molluscan eggs by confamilial snails (neritidae) and its potential significance in egg-laying site selection

Abstract: Neritid snails (Gastropoda: Neritimorpha) protect their eggs in a hard capsule, of tough conchiolin, reinforced by mineral particles derived from the faeces and stored in a special sac near the anus and oviduct opening. Predation on this arguably hardest of molluscan egg capsule is described and illustrated here; neritids of the freshwater to brackish-water genera Clithon and Vittina, generally classified as herbivores, feed facultatively on the eggs of various confamilial species after breaking the reinforced capsule lid by means of prolonged radular rasping. Intensive predation pressure by these common inhabitants in Indo-West Pacific coastal streams may have given rise to the remarkable egg-laying behaviour of Neritina on the shells of other living snails. Our laboratory examination showed that Neritina species deposited clusters of egg capsules more frequently on the living shell than on other substrates, and that the predation rate was significantly lower on this moving ‘nursery’. Predation rate was even lower on the small egg capsules of Clithon and Vittina themselves, which were deposited one by one in the depressions on the rough surfaces of stones.

Stable isotopes indicate individual level trophic diversity in the freshwater gastropod lymnaea stagnalis

Abstract: In lacustrine ecosystems, benthic grazers are generally thought to feed on sediment detritus and microalgae, although there is a paucity of information on food resource use within populations. In this study, we investigated individual level trophic signatures for grazing snails, Lymnaea stagnalis, along with primary consumers and producers in the same habitat, using carbon and nitrogen stableisotope analyses. In addition, we tested whether ontogeny and parasite presence influence food resource use. The large variation in d 13 C and d 15 N isotopic signatures indicated that individuals within a population feed on different food sources. Snails appear to have much greater individual variance in trophic behaviour than the other lacustrine species sampled (larval chironomid Chironomus plumosus, amphipods, Gammarus lacustris, zooplankton Ceriodaphnia sp. and Simocephalus vetulus). Moreover, variation among snails was not explained by shell length or the presence of parasitic infections. Habitat heterogeneity and resource availability at the microhabitat level may be the primary factors determining individual food sources.

The shell-bearing, benthic gastropods on the southern part of the continental slope off norway

Abstract: The fauna of benthic shell-bearing gastropods on the continental slope off western Norway is described, based on material collected during the 1980s. Almost 3,000 specimens belonging to 96 species have been studied. The existence of a specific gastropod fauna restricted to the upper slope is documented, and the fauna is compared with that of the shelf, the ‘lower’ slope and the abyssal (below c. 2,000 m) depths of the Norwegian Sea. Possible dependence of the slope fauna on the negative temperature of the Norwegian Sea water and on internal waves in the region of the thermocline is discussed. Some species found on the upper slope are illustrated.

The calcareous egg capsule of the patagonian neogastropod odontocymbiola magellanica: morphology, secretion and mineralogy

Abstract: Odontocymbiola magellanica is the only known South American volutid gastropod that deposits calcareous egg capsules. The spawn is moulded and fixed to flat or convex surfaces by the female’s ventral pedal gland, during an hours-long process in which the female adopts a stereotyped posture and appears nonreactive to most external stimuli. Microscopically, the different cells of the ventral pedal gland show features suggesting their participation in the secretion of both the organic matrix and the calcium component of the calcareous layer. The latter consists mainly of numerous spherspherulites that are packed together around cylindrical, septated spaces which traverse the spherspherulitic layer and attach to the membranous layers surrounding the capsule cavity. These septated spaces should ensure permeability of the capsule wall, which is necessary for gas exchange and excretion by the embryo. The calcareous layer is made of high-magnesium calcite, a calcium carbonate polymorph in which Ca is partially substituted by Mg in the calcite lattice. Mg substitution is thought to confer a greater crack resistance to the mineral; it is found in many invertebrates, but apparently has not been reported before in molluscs. Odontocymbiola magellanica is a long-lived species, investing heavily in its egg capsules.

Natural aestivation and antioxidant defence in helix pomatia: effect of acclimation to various external conditions

Abstract: During summer land snails are repeatedly exposed to low oxygen tension and to enhanced production of reactive oxygen species due to aestivation/arousal cycles. To test the role of reduced glutathione (GSH – the main endogenous antioxidant) and effect of season on its function we examined activities of glutathione-related enzymes and concentration of GSH in Helix pomatia snails (1) during their natural aestivation/arousal cycle in summer and (2) after their acclimation to different thermal and photoperiod conditions in autumn. Natural aestivation evoked decreases in activity of glutathione reductase (GR) in the hepatopancreas and kidney and an increase in activity of glutathione transferase (GST) in the hepatopancreas, but did not affect activity of glutathione peroxidase (GPX) and concentration of GSH in these organs. Activities of GR in both organs and GST in the kidney were highly affected by acclimation to summer-specific ambient conditions, whereas activity of GPX and GSH concentration were affected by acclimation to 258C at a short-day photoperiod. In conclusion, H. pomatia maintains relatively high organ concentrations of reduced glutathione but can also modulate its enzymatic antioxidant defence system according to environmental conditions.

Sequence variation of the internal transcribed spacer (ITS) region of ribosomal DNA in Cerastoderma species (Bivalvia: Cardiidae)

Abstract: The internal transcribed spacer (ITS) region of ribosomal DNA (ITS1, 5.8S rRNA gene and ITS2) constitutes one of the most widely applied molecular markers in phylogenetic studies and species differentiation. Here, the ITS region of the cockles Cerastoderma edule from NW Spain and C. glaucum from the Mediterranean and Baltic Seas was characterized and its variation examined. The length of the ITS was 762–783 bp (ITS1, 226–251 bp; 5.8S rRNA gene, 158–161 bp; ITS2, 305–325 bp) and the GC content ranged between 57% and 60% (ITS1, 52–62%; 5.8S rRNA gene, 56–57%; ITS2, 61–63%). All individuals showed variation among ITS repeats, mostly in the spacers, with nucleotide diversity values of 0.0005–0.07. Among the C. glaucum sequences, two types of ITS (ITSI and ITSII) were distinguished, based on the percentage of differences observed in the spacers, sequence of the 5.8S gene, GC content of the ITS1 and clustering in phylogenetic trees. A PCR assay using specific primers for each ITS type demonstrated that both types coexist in all C. glaucum individuals. While type I seems to contain the bona fide 5.8S rRNA gene, type II could contain a pseudogene. Cerastoderma edule sequences grouped separately on phylogenetic trees, as expected for a differentiated species, but those of C. glaucum from the Mediterranean and Baltic Seas were intermixed in the two clades defining the ITS types, which supports the absence of systematic division previously inferred from other molecular markers.

Testing the habitat harshness hypothesis: reproductive biology of the wedge clam donax hanleyanus (bivalvia: donacidae) on three argentinean sandy beaches with contrasting morphodynamics

Abstract: In order to test the habitat harshness hypothesis (HHH) the reproductive biology of Donax hanleyanus was studied histologically, comparing populations from three beaches with contrasting morphodynamics (dissipative, intermediate and reflective) over 25 months. The reproductive phase of D. hanleyanus was extended at the reflective beach compared to the other two. Males and females from the dissipative and intermediate beaches were significantly smaller and had lower biomass at maturity than those at the reflective beach. Recruits were significantly more abundant and the recruitment period was extended significantly at the dissipative beach. Spawning events took place twice each year at the dissipative (early spring and spring-summer) and the intermediate beach (winter and summer), whereas continuous gamete releases were noted at the reflective beach. Size and biomass at first maturity were lower at the dissipative beach, whereas monthly mean abundance of D. hanleyanus was higher at the reflective beach. The gametogenic cycle correlated significantly with sea-surface temperature, relative spermatozoon abundance, condition index, ash-free shell-free dry mass, and mean size and abundance of oocytes, for all three populations. At the population level, many of these reproductive responses to physical variables were opposite to those predicted by the HHH, including: greater abundance, extended reproductive cycle, extended period with spawning individuals, and larger size and higher biomass at first maturity at the reflective beach. This suggested that the hypothesis of habitat safety (HHS), originally proposed for supralittoral species, may be extended to intertidal species; a combination of narrow swashes and steep slopes makes reflective beaches a safer and more stable environment for intertidal species such as D. hanleyanus.

Localization of serotonin in neuronal ganglia of the freshwater pearl mussel, Hyriopsis (Hyriopsis) bialata

Abstract: We investigated the histological features of neuronal ganglia and the localization of serotonin in the unionid mussel Hyriopsis (Hyriopsis) bialata in Thailand. The long-term goal of this study is to apply endocrine manipulation to enhance the synchronous release of larvae for in vitro culture of this freshwater mussel and to increase larval survival during settlement. Unlike the case in other bivalves, the cerebropleural ganglia in H. bialata were completely fused to form a single pear-shaped structure, and the pedal ganglia were situated within the visceral mass rather than in the foot. In all three ganglia of this mussel, the neuronal cell bodies were clustered at the periphery of the ganglia, and the nerve fibres were bundled in the central region. Of the three types of cells present in the ganglia, the large neurons were the only ones to stain with paraldehyde fuchsin, indicating a neurosecretory function. These same neurons were also intensely reactive with anti-serotonin, demonstrating their dual function. An intense staining of anti-serotonin was also observed in the nerve fibres and termini, particularly in the visceral ganglia. This suggests that serotonin may be conveyed from the large neurons within the visceral ganglion via an axonal route to reach the target reproductive organs, one of which is the demibranch, to stimulate larval release in this mussel.

The phylogeny of the Acteonoidea (Gastropoda): molecular systematics and first detailed morphological study of Rictaxis punctocaelatus (Carpenter, 1864)

Abstract: The Acteonoidea are a taxon of about 150 species with uncertain systematic affinity. They have been variously regarded as basal Opisthobranchia, as Architectibranchia, or placed basal to Opisthobranchia together with other heterobranch clades with uncertain interrelationships. We performed molecular phylogenetic analyses employing four gene markers (nuclear 18S rDNA and 28S rDNA; mitochondrial 16S rDNA and COI) to reassess the phylogenetic position of Acteonoidea and provide the first comprehensive study on interrelationships of the constituent families. Our analyses reveal a sister-group relationship of the Acteonoidea to the ‘lower’ heterobranch taxon Rissoelloidea, implying a basal placement outside the Opisthobranchia. However, the Acteonoidea/Rissoelloidea clade is sister group to the morphologically derived opisthobranch clade Nudipleura, implying an opisthobranch origin. Regarding the interrelationships of the Acteonoidea, the current division into three families is challenged by recovery of only two clades. The genus Bullina (sole genus in Bullinidae) resolves as a member of the Aplustridae, which is thus rendered paraphyletic. The Acteonidae are paraphyletic due to the strongly supported position of Rictaxis punctocaelatus basal to the Aplustridae. The first detailed investigation of the morphology and histology of R. punctocaelatus revealed similarities with both Acteonidae and Aplustridae, implying an intermediate position. Owing to the placement of R. punctocaelatus basal to the Aplustridae, the shared acteonid characters are therefore considered plesiomorphic for the whole Acteonoidea and are probably the features of the last common ancestor of the clade.

Topographical distribution of visual cell nuclei in the retina in relation to the habitat of five species of Decapodiformes (Cephalopoda)

Abstract: Studies of retinal histology of fish have established that the position of an area of high cell density reflects both the habitat and feeding behaviour. Here, we discuss potential relationships between biology, specifically behaviour and ecology, and visual axes (estimated from density of visual cell nuclei) in five species of Decapodiformes. In all species, the posterior retina had the highest cell density. In coastal species, the region of highest density was dorsal to the midline of the body, meaning that the visual axis was likely directed downwards and forwards, suitable for focusing on the sea bottom. In oceanic species, the highest density region was ventral to the midline, meaning that the visual axis was directed upwards and forwards. This may be advantageous for detecting prey silhouetted against light from above in the open ocean.

Occurrence of Sporozoa-like microorganisms in the digestive gland of various species of Strombidae

Abstract: The digestive gland of Strombus (Eustrombus) gigas Linnaeus,1758 has been described by Gros, Frenkiel & Aldana Aranda(2009) as an assemblage of tubules and ducts that are con-nected to the stomach. Three cell types occur in the epitheliumof the blind-ending tubules, according to histological andTEM observations: digestive cells, crypt cells and vacuolatedcells. Several examples of parasitic relationships betweenmarine gastropods and apicomplexan parasites have beendescribed (Friedman et al., 1995; Azevedo & Padovan, 2004).Baqueiro Ca´rdenas et al. (2007) reported the presence of intra-cellular microorganisms that they interpreted as belonging tovarious life cycle stages characteristic of Apicomplexa withinsome cells in the digestive gland of S. gigas. Heterospecificinteractions between organisms living inside the cells ofanother one are not easy to characterize. The description ofSporozoa-like microorganisms occurring in the digestive glandof S. gigas raises several questions: How broad is the geographicdistribution of the Sporozoa-like microorganism? Are otherspecies of Strombidae also infected? The present study reportsthe occurrence of Sporozoa-like microorganisms from a struc-tural analysis of the digestive gland of six species belonging tothe family Strombidae found in distant geographic regions.Individuals from four Caribbean species: Strombus (Aliger)costatus Gmelin, 1791 (n ¼ 50); S. (Aliger) gallus Linnaeus, 1758(n ¼ 1); S. (Eustrombus) gigas (n

The ecological significance of growth rate, sexual dimorphism and size at maturity of Littoraria zebra and L. variegata (Gastropoda: Littorinidae)

Abstract: Growth rates, maturation sizes and sexual dimorphism in shell morphology (size, globosity and thickness) of Littoraria zebra and L. variegata in a mangrove forest at Malaga Bay (Pacific Coast of Colombia) were studied. The sexes of L. zebra did not show differences in growth rate or maximum size. Minimum sizes at maturity were similar; however, the mean size of mature males was smaller than that of females. Littoraria zebra did not show sexual dimorphism in shell morphology. Females of L. variegata grew almost twice as fast as males, reached larger maximum size and attained sexual maturity at a larger size than males. Females had thinner and more globose shells than males. Littoraria zebra and L. variegata reach sexual maturity at a relatively later stage than other Littorininae species, but they continue growing after maturity. The intersexual pattern of growth, in which males are smaller than females and grow more slowly, is common in Littorininae; however, L. zebra does not seem to follow this pattern. Sexual dimorphism of L. variegata can be explained by the hypothesis of fecundity selection and results from the difference in growth rates. The differences between the two species regarding shell thickness and growth rates are discussed in terms of vertical zonation and predation in the mangrove environment.

New evidence of functional suckers in belemnoid coleoids (Cephalopoda) weakens support for the ‘Neocoleoidea’ concept

Abstract: The idea of a sister-group relationship between the cephalopod superorders Decabrachia (squids and cuttlefishes) and Vampyropoda (octopods, cirroctopods and vampire squid) has been widely accepted since Jeletzky (1966: fig. 2). In their phylogenetic analyses, Berthold & Engeser (1987) and Engeser & Bandel (1988) regarded the presence of suckers as a character state that supports the monophyly of what they called the ‘sucker-bearing Coleoidea’. In 1997, Haas introduced the terms ‘Neocoleoidea’ for coleoid groups with living representatives and ‘Palaeocoleoidea’ for a group of hook-bearing coleoids also known as ‘Belemnoidea’, which was thought to have disappeared at the end of the Cretaceous. Like Berthold & Engeser (1987) and Engeser & Bandel (1988), Haas (1989: 166; 1997: 64, fig. 9; 2002: 341, text-fig. 1; 2003: 114, fig. 1) detected only one character state uniting the ‘Neocoleoidea’, the ‘presence of suckers’. Although von Boletzky (1992) found strong arguments against the monophyletic origin of the group later called ‘Neocoleoidea’, Young, Vecchione & Donovan (1998: fig. 1) followed Haas (1997) and adopted the ‘Neocoleoidea’ concept. Phylogenetic analyses including morphological and/or molecular data sets have subsequently assumed that the ‘Neocoleoidea’ are a monophyletic group and that the ‘Belemnoidea’ represent its extinct sister-group (e.g. Young & Vecchione, 1996; Vecchione, Young & Carlini, 2000; Lindgren, Giribet & Nishiguchi, 2004; Strugnell & Nishiguchi, 2007). Thus, the ‘Neocoleoidea’ concept is chiefly based on the presumed absence of suckers in belemnoids, although equivocal evidence for their presence has existed for some time. Mantell (1852: 19, fig. 4) probably observed suckers in Belemnotheutis antiquus Pearce, 1847, a belemnoid from the middle Jurassic (Callovian; 164 Ma) Oxford Clay of Christian Malford (UK). Engeser & Clarke (1988: 139) suggested that these structures instead represented muscles that moved the hooks and that they were unlikely to be functional suckers. In their redescription of the type material of B. antiquus, Donovan & Crane (1992: 286), however, recorded sucker-like structures in a second specimen from the same area and described them as follows: “Where suckers are preserved there are the same number of pairs of hooks as suckers, but it is not clear whether the hooks are rooted in the suckers, as they sometimes appear to be (Pl. 2 fig. 2). There could have been only one row of suckers per arm. Distal suckers are smaller than proximal ones, the largest being about 2 mm in diameter. Several suckers show what could have been a chitinous ring around the outside (Pl. 2 fig. 4)”. Their observations led them to conclude that “. . .the presence of suckers in Belemnotheutis shows that suckers are not autapomorphic for Dibranchiata sensu Berthold and Engeser. . .” and that “. . .it is likely that suckers were already present in the common ancestors of the Belemnitida and the living forms”. Both Young et al. (1998: 395) and Fuchs (2006: 71, 77, fig. 3.7–3) later expressed doubts about the existence of functional suckers in belemnoids. We report here a new record of a belemnoid arm crown with exceptionally preserved soft parts including apparent suckers, which again question the monophyly of the ‘Neocoleoidea’. The isolated arm crown comes from the late Jurassic (Tithonian; 150 Ma) limestones of Eichstatt (southern Germany). The specimen (Coll. H. Tischlinger, catalogue no. 98/3) is flattened and consists of slab and counter slab. Most probably, the arm crown belongs to the genus Acanthoteuthis Wagner in Munster, 1839, a common belemnoid genus in the Eichstatt limestones and close relative of Belemnotheutis Pearce, 1842. It consists of 10 equal arms (maximum arm length 12 cm), each of which shows well-preserved imprints of hooks and suckers (Fig. 1A–F). Observations under UV light indicate that the proximal arm musculature is preserved as calcium phosphate and that five arms cover the remaining arms (Fig. 1B). The plane in which the arm crown has been embedded is unclear; identification of ventral and dorsal arms is therefore impossible. Although distal arm musculature is not preserved, the position of each arm can be reconstructed through the arrangement of hook and sucker imprints (Fig. 1C). Hook imprints, which are generally filled with calcite, suggest a biserial arrangement as is typical for belemnoids (Fig. 1D–F). Only few hooks are visible as brownish staining. The shape of the paired hooks is variable along each arm as described by Engeser & Reitner (1992) for Acanthoteuthis from the Eichstatt region. Apart from the hooks, each arm is equipped with one series (1⁄4 longitudinal row) of circular suckers (because the arm crown consists of part and counterpart, upper as well as lower arms left sucker imprints). The suckers appear very close to the arm bases. The sucker diameter increases gradually from proximal to one half the arm length and then decreases distally. The largest sucker imprints are 5 mm in diameter, the smallest 2 mm. We counted a maximum number of 19 suckers per arm. The best preserved sucker imprints exhibit another circular imprint in their centre (Fig. 1F). This inner circle can be interpreted as the opening of a suction chamber of the acetabulum; this would strongly suggest that this is, indeed, a sucker. If so, the periphery would correspond to the imprints of the infundibulum. It is important to note that there is no evidence of horny rings as are typical for decabrachian suckers. The present suckers seem to be identical to those illustrated and described in Donovan & Crane (1992: pl. 2) but, in contrast to their specimen, our new record unambiguously shows that the hooks are not rooted within the suckers (Fig. 1D–F). Instead, the paired hooks clearly alternate with the unpaired suckers. In particular, the latter observation demonstrates the

Histomorphology of the hypobranchial gland in Dicathais orbita (Gmelin, 1791) (Neogastropoda: Muricidae)

Abstract: Tyrian purple is a dye used in antiquity and is a natural product of marine molluscs of the family Muricidae. Bioactive precursors of Tyrian purple occur in the hypobranchial gland, reproductive glands and egg masses of muricids, such as Dicathais orbita. Histomorphological examination of the hypobranchial–gonoduct complex (rectum and hypobranchial, capsule, albumen and rectal glands) was conducted to provide the first description of the hypobranchial gland in D. orbita and to determine a mechanism for the transfer of Tyrian purple precursors to the gonoduct and ultimately to the egg masses. Seven secretory cell types were identified in the hypobranchial epithelium of D. orbita, which can be broadly classified into cells containing mucoproteins and acidic sulphated mucopolysaccharides. Three secretory cells new to the Muricidae were identified, along with two cell types that appear to be associated with synthesis of Tyrian purple. A subepithelial vascular sinus surrounding the rectum and rectal gland occurs between the hypobranchial gland and gonoduct. Examination of this region failed to reveal a direct anatomical mechanism for the transfer of precursors to the gonoduct. However, biochemical similarities in secretions from the hypobranchial, capsule and albumen glands suggest that the synthesis of precursors within the gonoduct may be possible.

Reproduction of the vermetid gastropod Dendropoma maximum (Sowerby, 1825) in Moorea, French Polynesia

Abstract: Vermetidae are sessile molluscs with tubular shells cemented to the substrate. Although they are common inhabitants of coral reefs and rocky shores, little is known about the basic biology of most species. Dendropoma maximum is the largest vermetid species and is common across its Indo-Pacific range. Here we report on a study of reproductive and morphological traits in D. maximum from the lagoon around Moorea, French Polynesia. Both body length and diameter of shell aperture (generally the only visible part of the animal in the field) were good predictors of body weight and this relationship did not differ between males and females. Shell apertural diameter is therefore a good index of body size in D. maximum. The sex ratio became increasingly dominated by females with increasing body size, which is suggestive of protandric hermaphroditism. Probability of brooding, the number and size of brooded egg capsules, and the number of embryos per capsule were all positively related to female size. Females released veliger larvae that lived without additional food for up to 10 days, but were observed to feed when offered cultured phytoplankton on the final day. This is the first direct observation of feeding by larvae in this genus, and a planktotrophic larval stage has implications for potential dispersal in D. maximum.

Predation impacts of the invasive flatworm platydemus manokwari on eggs and hatchlings of land snails

Abstract: Some species of terrestrial planarians (flatworms) are among the predators of land snails, but their predatory impacts have not been sufficiently studied. Flatworms are known to follow snail trails to find prey and enter shells to consume snails; however, eggs (which do not have trails to follow) and snails whose shells are too small for flatworms to enter may not be eaten. To determine whether an invasive flatworm, Platydemus manokwari, preys on snail eggs or small land snails, we conducted a laboratory experiment in which we fed five eggs or five hatchlings (2 mm in diameter) of a common land snail species found in Japan to P. manokwari individuals of various sizes. Egg predation did not occur within 10 days, but hatchling predation commenced on the first night; only 9% of the hatchlings remained on Day 10. Platydemus manokwari did not recognize early-stage eggs as food, but started preying on eggs just before they hatched. Flatworms can therefore be a significant predator on land snails, preying on even tiny land snails, leaving only early-stage eggs free from predation.

Anatomy and affinities of Micropilina minuta Warén, 1989 (Monoplacophora: Micropilinidae)

Abstract: The anatomy of the tiny (maximum shell length 1.5 mm) monoplacophoran limpet Micropilina minutaWaren, 1989 was studied by means of semithin serial sections with subsequent 3D computer analysis and visualization (interactive 3D model in the online version). As in other monoplacophorans there are eight pairs of shell muscles (‘sectors’ A–H). The species has four pairs (unique for monoplacophorans, sectors D–G) of small gills, four pairs of kidneys (sectors A, D–F) which also have gamete-releasing function (sectors D, E), and one (or two) pair(s) of gonadal sacs. Eggs are yolk-rich, but there are no signs of retention of eggs in the mantle cavity for brooding. Only some of these characters, particularly those connected with miniaturization, are shared with Micropilina arntzi. Two characters (absence of a heart and absence of sector G kidneys) are interpreted as synapomorphies of these two species. Based on these new data the supraspecific systematics of Micropilina and Micropilinidae are reevaluated. We also discuss the implications for the evolution of the serial arrangement of organs in the Neopilinoidea.

Female copulatory status and male mate choice in neptunea arthritica (gastropoda: buccinidae)

Abstract: Male mate choice in Neptunea arthritica was investigated in copulation trials, where female copulatory status and intermating interval were manipulated. Males preferred recently copulated to noncopulated females and did not discriminate between single- and twice-copulated females. Our results show a startling divergence from the results reported in other study models, with significant implications for our general understanding of the way sperm competition shapes male mate choice. We discuss the importance of female copulatory status, female intermating interval and sperm removal probability as factors extending competitive scenarios among males and how preference for recently copulated females might be maintained.