Journal of Molluscan Studies - recent issues

Margaritifera marocana (Pallary, 1918): a valid species inhabiting Moroccan rivers

Araujo, R., Toledo, C., Van Damme, D., Ghamizi, M., Machordom, A. — 2009-04-13

Within the Unionoida the family Margaritiferidae is a small but widely distributed group, whose number of genera and species is under discussion. Using molecular and morphological characters, the present paper redescribes several Moroccan specimens of Margaritifera, previously classified as M. auricularia marocana. The shell and anatomical features of the taxon are similar to those observed in European specimens of M. auricularia auricularia. Notwithstanding, the two subspecies can be separated by certain hinge characters. Partial sequences of the mitochondrial genes COI and 16S rRNA support recognition of the Moroccan populations as a different species: Margaritifera marocana. We examined the phylogenetic relationships of the Margaritiferidae. The COI data indicated two monophyletic clades: one including M. margaritifera, M. dahurica, M. falcata and M. laevis, and the second comprising M. auricularia from the Iberian Peninsula and the Moroccan specimens of M. marocana as an independent lineage. Cumberlandia monodonta was recovered as the basal margaritiferid, sister to Margaritifera.

Comparison of gill surface morphology across a guild of suspension-feeding unionid bivalves

Galbraith, H. S., Frazier, S. E., Allison, B., Vaughn, C. C. — 2009-04-13

Freshwater mussels are found in dense, multi-species aggregations where the potential for resource partitioning should be high. One means by which mussels may be partitioning resources is through feeding on different food items. We compared gill morphology in four species of co-occurring freshwater mussels. We found differences in total gill surface area, density of latero-frontal cirri and the number of cilia per cirral plate, with one species, Actinonaias ligamentina, having the largest gills with densest cirral plates relative to the other three species. These differences in feeding structures might allow these species to utilize different food resources, or could be related to other functions performed by the gills, including respiration or brood storage.

The phylogeny and biogeography of the genus Zonites Montfort, 1810 (Gastropoda: Pulmonata): preliminary evidence from mitochondrial data

Kornilios, P., Poulakakis, N., Mylonas, M., Vardinoyannis, K. — 2009-04-13

The genus Zonites, which includes 26 extant species, is distributed in the northeastern Mediterranean area and exhibits significant diversity and endemism. This is the first phylogenetic study of Zonites, based on partial mitochondrial DNA sequences of the 16S rRNA gene. A total of 43 specimens, belonging to 15 species from 39 localities in Greece and Turkey, were included. Analyses revealed two major clades, corresponding to two distinct geographic regions, west and east of the mid-Aegean trench. The palaeogeography of the Aegean and the plasticity of the Zonites shells have produced a great variety of forms that have been identified as different species or subspecies. Our results, although preliminary, suggest that the taxonomy of Zonites requires revision. We propose an historical interpretation of the present distribution of Zonites, based on the palaeogeographic history of the Aegean region.

Effect of attachment status and aggregation on the behaviour of the zebra mussel Dreissena polymorpha

Kobak, J., Poznanska, M., Kakareko, T. — 2009-04-13

The zebra mussel Dreissena polymorpha lives attached to a hard substratum, often in dense aggregations. It can thus be expected that both its attachment status and conspecifics may greatly affect its responses to various environmental stimuli. We studied whether the attachment status influenced mussel relocation frequency and responses to light and gravity in laboratory conditions. We also tested the impact of conspecifics upon mussel attachment strength and relocation frequency. Small (<10 mm) and large (>10 mm) mussels attached for 1 or 6 days relocated from their initial positions less frequently than unattached individuals. Large mussels crawled less often than small individuals, but neither attachment status nor size modified their responses to light: illuminated (100 lx) mussels always moved towards dark areas and changed their initial sites less often than those kept in darkness. On a slope inclined at 8°, unattached small mussels preferred upward movement in darkness whereas large mussels moved similarly in both directions and were less mobile than small individuals. The behaviour of mussels attached for 6 days was reversed: negative geotaxis disappeared in small mussels, while large mussels preferred to crawl upwards and moved more often than small individuals. Aggregated mussels of both size groups were more strongly attached to the substratum and stayed at their initial sites more often than singletons. Our study shows that attachment status and conspecifics can modify responses of zebra mussels to environmental stimuli and should be taken into account in behavioural studies on this species.

Does a shell matter for defence? Chemical deterrence in two cephalaspidean gastropods with calcified shells

Neves, R., Gaspar, H., Calado, G. — 2009-04-13

Opisthobranch molluscs show an evolutionary trend to reduce, internalize and lose the shell. Many of them base their defensive strategies on natural deterrent products and current evolutionary theory suggests that the acquisition of chemical defences preceded shell reduction and loss, which has characterized the evolution of this group. Here we show that basal, shelled opisthobranch molluscs are defended against sympatric predators even if their protective shell is removed. The cephalaspideans Bulla striata and Haminoea orbignyana, both with distinct shell calcification, significantly deterred feeding by sympatric crab and fish predators, both in laboratory and field assays. However, our results argue against a progressive increment of chemical defences associated with shell reduction, because the cephalaspidean with the more fully calcified shell, Bulla striata, was also the more deterrent. These findings suggest that effective chemical defences might have evolved independently from shell loss, at least in basal opisthobranchs such as cephalaspideans.

Effects of competition on size and growth rates of Caracolus caracolla (L.) in Puerto Rico

Bloch, C. P., Willig, M. R. — 2009-04-13

Although interspecific competition has been demonstrated between some pairs of terrestrial gastropod species, little work addresses its importance in tropical assemblages, which are often characterized by high species richness or population densities. A 9-year data set was used to assess growth rates and median shell size of a common Puerto Rican snail, Caracolus caracolla, as a function of density of conspecifics and potential interspecific competitors. Neither the rate nor the magnitude of growth of C. caracolla were inhibited at high densities. No association existed over time between density and size or growth rate. In contrast, C. caracolla generally was largest at sites with high densities of conspecifics. Several factors may be responsible for the apparent unimportance of competition, including the broad, flexible diet of C. caracolla, high productivity of the study site or periodic changes in microclimate or resource availability associated with hurricane-induced disturbance and recovery.

Identification of seven Crassostrea oysters from the South China Sea using PCR-RFLP analysis

Xia, J., Yu, Z., Kong, X. — 2009-04-13

We have developed a PCR–RFLP assay of two mitochondrial [16S rDNA and cytochrome oxidase I (COI)] and one nuclear (ITS-1) gene fragment for the identification of seven Crassostrea oysters from the South China Sea. These include the morphologically distinct Crassostrea sikamea and three pairs of morphologically similar species: Crassostrea hongkongensis and Crassostrea ariakensis, Crassostrea gigas and Crassostrea angulata, Crassostrea iredalei and an unidentified Crassostrea sp. All seven species can be distinguished with both mitochondrial markers: DdeI/DraI or AluI/MseI digestion of 16S rDNA and NisI/AluI or NisI/DdeI digestion of COI. Five of the seven species can be distinguished using a single endonuclease digestion of the ITS-1 fragment. Based on genetic distance estimates and on morphology, the newly discovered Crassostrea sp. appears most closely related to C. iredalei. Despite the existence of intra-specific variation at low frequency in some restriction sites, the PCR–RFLP assay developed here can be reliably applied to identify all seven oyster species.

Predatory behaviour of the naticid Euspira fortunei: why does it drill the left shell valve of Ruditapes philippinarum?

Hasegawa, H., Sato, S. — 2009-04-13

Field observations showed that at two sites in northern Japan, the invasive naticid gastropod Euspira fortunei preferentially drills the left shell valve of the bivalve Ruditapes philippinarum. Laboratory experiments revealed that when R. philippinarum was allowed to adopt its normal life position, there was a statistically significant preference for E. fortunei to drill the left rather than right shell valve. Further observations of the predatory behaviour of E. fortunei showed that: (1) because this species lifted the left side of its foot while catching R. philippinarum, the direction of the apex of this snail's shell usually coincided with that of the clam's anterior margin; (2) the snail turned its prey around the axis of the anterior and posterior margin; (3) and that if the snail drilled the right shell valve of R. philippinarum, the foot and siphons of the clam interfered with its predatory behaviour.

Substrate selection by the freshwater mussel Diplodon chilensis (Gray, 1828): field and laboratory experiments

Lara, G., Parada, E. — 2009-04-13

To evaluate the capacity for movement of freshwater mussels in sandy and sand-gravel substrates and to test their ability to differentiate among types and qualities of substrates, experiments were carried out in the laboratory and in the field, using Diplodon chilensis from Lake Panguipulli, Chile. The movement of mussels was greater in sandy than in sand-gravel substrates. In the absence of food, there was a significant preference for sandy substrate, and when mussels were offered sandy or sand-gravel substrates with and without food they chose the substrate with food with no preference to substrate type. Under natural conditions mussel presence and abundance along time is regulated by variables with a synergistic effect, niche of which substratum is not always the major one.

Sperm ultrastructure and spermatogenesis in the hydrothermal vent gastropod Rhynchopelta concentrica (Peltospiridae)

Hodgson, A. N., Eckelbarger, K. J., Young, C. M — 2009-04-13

The sperm and spermatogenesis in the aphallic hydrothermal vent gastropod Rhynchopelta concentrica are described by transmission electron microscopy. Only euspermatozoa were found in the specimens studied. Spermatozoa are filiform introsperm, confirming that this species has internal fertilization. The sperm have an elongate nucleus (which has an intranuclear canal for most of its length) capped by a needle-like acrosome that is invaginated posteriorly. A small basal plate lies between the base of the acrosome and the nucleus. The mid-piece consists of numerous small mitochondria with poorly developed cristae housed in a cytoplasmic sleeve, the inner region of which forms an electron-dense tube extending along the axoneme. As is typical of vetigastropod and neritimorph sperm, there is no glycogen piece. Spermatogenesis is similar to that described for many gastropods, although aspects of nuclear and mid-piece/flagellum formation resemble those described for neritimorphs.

Diversity and reproduction of near-shore vs offshore wood-boring bivalves (Pholadidae: Xylophagainae) of the deep eastern Pacific ocean, with three new species

Voight, J. R. — 2009-04-13

The ability of obligate wood-boring bivalves of the Xylophagainae to colonize wood seemingly wherever it lays on the seafloor remains enigmatic. The continuous, if patchy, deposition of vegetation in near-shore deep-water areas is hypothesized to allow woodborers to develop opportunistic species that exploit offshore wood falls and to produce larvae that colonize isolated wood-falls on the distant seafloor. Examination of specimens and literature accounts from near-shore (within 1.5° longitude of the continent) and offshore (more than 2.3° longitude from the continent) areas tests the hypothesis that the same species occur in both areas. The hypothesized role of near-shore populations as sources of offshore colonists is refuted; the 18 species of Xylophagainae documented in the Northeast Pacific Ocean appear to form two nearly distinct groups based on their proximity to the continent. Of 11 near-shore species of Xylophagainae recorded off western North America, including three (Xylophaga siebenalleri n. sp.; X. pacifica n. sp., Xylopholas scrippsorum n. sp.) described here, only one is also known from offshore sites. Four near-shore species are documented to range from the San Diego Trough to Oregon, including three that apparently brood young. Brooded young are considered to restrict the offshore dispersal of species, but not to limit their movement along the continental margin.

Ctenidial structure and three bacterial symbiont morphotypes in Anodontia (Euanodontia) ovum (Reeve, 1850) from the Great Barrier Reef, Australia (Bivalvia: Lucinidae)

Ball, A. D., Purdy, K. J., Glover, E. A., Taylor, J. D. — 2009-04-13

The structure of the ctenidia of the Indo-West Pacific chemosymbiotic lucinid bivalve Anodontia (Euanodontia) ovum was investigated by electron microscopy. Ctenidial filaments are similar in general morphology to those described from other Lucinidae, with a ciliated zone, a short intermediary zone and a thick abfrontal zone composed largely of bacteriocytes separated by narrow intercalary cells. The bacteriocyte zones of adjacent filaments are fused in the distal part to form short cylindrical channels. The apices of intercalary cells project as cytoplasmic protrusions in the form of spiky tufts, with sheets and tendrils spreading over adjacent bacteriocytes. Compared with other lucinids A. ovum lacks abfrontal granule cells, mucocytes are infrequent and the bacteriocyte channels are short. Three morphotypes of symbiotic bacteria were detected, associated with the bacteriocyte zone of the ctenidial filaments: (1) all bacteriocytes contained abundant bacteria 3–5 µm long and 0.5–1.0 µm wide, enclosed in single vacuoles; (2) some bacteriocytes possessed spherical vesicles enclosing masses of smaller rod-shaped bacteria c. 1.0 µm long; (3) probable spirochaete bacteria, 8–10 µm long and 0.3 µm wide, were abundant within the apical cytoplasmic protrusions of the intercalary cells. Preliminary molecular analysis using 16S rRNA gene sequences has so far identified only one bacterial symbiont, from the gamma division of Proteobacteria grouping in a cluster of symbiotic thiotrophs. This symbiont of A. ovum is closely similar to a symbiont previously reported from the western Atlantic lucinid Anodontia schrammi (originally cited as A. philippiana).

Application of a DNA barcode using the 16S rRNA gene to diagnose pest Arion species in the USA

Barr, N.B., Cook, A., Elder, P., Molongoski, J., Prasher, D., Robinson, D.G. — 2009-04-13

Transport of cuttlefish, Sepia officinalis, eggs under dry and damp conditions

Jones, N.J.E., Ridgway, I.D., Richardson, C.A. — 2009-04-13

Field collection of Laevipilina hyalina McLean, 1979 from southern California, the most accessible living monoplacophoran

Wilson, N. G., Huang, D., Goldstein, M. C., Cha, H., Giribet, G., Rouse, G. W. — 2009-04-13

A comment on F. Aguado & A. Marin: 'Warning coloration associated with nematocyst-based defences in aeolidioidean nudibranchs'

Penney, B. K. — 2009-04-13

Chemical or nematocyst-based defence in the nudibranch Cratena peregrina? - a reply to B.K. Penney

Marin, A. — 2009-04-13

Do nematocysts sequestered by aeolid nudibranchs deter predators? - a background to the debate

Edmunds, M. — 2009-04-13

Morphological and anatomical differentiation of three land snails of the genus Rhynchotrochus (Gastropoda: Pulmonata: Camaenidae)

Jordaens, K., Bruyndoncx, L., Van Goethem, J., Backeljau, T. — 2009-01-13

Land snails of the Papua New Guinean camaenid genus Rhynchotrochus are described on the basis of shell shape, shell colour and banding pattern. We compared morphological and anatomical differentiation in three of the species, viz. R. albocarinatus, R. taylorianus and R. williamsi. The three species can be distinguished by their shell colour and banding pattern, as well as by their shell and reproductive morphology. Rhynchotrochus albocarinatus has a white, subglobose shell with up to five bands and a white to chocolate-brown outer lip. The penis is longer than the vas deferens and the length of the oviduct (LO) is approximately one-third that of the vagina. The subdepressed, trochiform shell of R. taylorianus is highly variable with respect to shell colour and banding pattern. The penis is approximately as long as the epiphallus and shorter than the vas deferens; the LO is approximately two-thirds that of the vagina. Rhynchotrochus williamsi has a white, unbanded, globose shell with a white to light pink outer lip and a dark protoconch. The penis is markedly shorter than the vas deferens or epiphallus which are approximately of the same length; the oviduct is approximately half as long as the vagina. Within R. taylorianus, there is substantial variation in shell colour, shell banding pattern and reproductive morphology that may confuse identification. We also document on one specimen of R. albocarinatus that has two interconnected penises. Since both penises were not connected to the spermoviduct, copulation as a male should have been prevented in this specimen.

Heat tolerance in Mediterranean land snails: histopathology after exposure to different temperature regimes

2009-01-13

The physiological and biochemical adaptation mechanisms of heat-tolerant snail species are poorly known. We investigated cellular adaptations to heat stress in four heat-exposed snail populations (two of Xeropicta derbentina, one each of Cernuella virgata and Theba pisana). Snails were exposed to different temperature regimes (25, 33, 38, 40, 43, 45, 48, 50 and 52°C) in the laboratory for 8 h. After exposure, immobility rates were determined and a qualitative and semi-quantitative histopathological analysis of the digestive gland (calcium and digestive cells) and mucocytes in the foot was conducted. In addition, the coloration of the shells was densitometrically determined. The shells of T. pisana were significantly darker than the shells of the other populations. The immobility rates and histopathological examinations showed that X. derbentina (both populations) was slightly better adapted to heat than C. virgata, and much better adapted than T. pisana. The observed differences in heat tolerance seemed to be connected to the ability for rapid and extreme proliferation of calcium cells in the digestive gland.

Reaction norms of size and age at maturity of Pomacea canaliculata (Gastropoda: Ampullariidae) under a gradient of food deprivation

Tamburi, N. E., Martin, P. R. — 2009-01-13

Pomacea canaliculata, an apple snail native to South America, has become a serious pest of aquatic crops and a promoter of ecosystem changes in natural wetlands worldwide. Its success as an invader has been attributed to its great phenotypic plasticity in life-history traits. Our aims were to determine the reaction norms of size and age at maturity under a gradient of food deprivation. Full sibling experimental snails were reared in isolation from hatching and maintained until maturity under seven different levels of relative food deprivation based on size-specific ingestion rates. To detect the onset of sexual activity of experimental snails, fully mature virgin snails reared in the laboratory were used as consorts. The reaction norms for age and size at maturity of P. canaliculata showed marked sexual dimorphism. Shell length was the main component of variation in the male reaction norms for both copulation and egg-laying by female consorts, whereas age was the main component of variation for females. Irrespective of the intensity of food deprivation, males mature at the same age at the expense of size, since size is apparently irrelevant in the access to females and male fitness can be maximized through fast maturation. In contrast, a minimum size is required for females to reach maturity, perhaps as a result of their higher reproductive costs. The highly dimorphic reaction norms lead to an increasing lag between male and female maturity as deprivation increases; in temperate regions, males born early in the reproductive season would mature in the same season irrespective of food availability, while most females would have to overwinter before attaining sexual maturity in unproductive habitats or those dominated by unpalatable macrophytes. The great life-history plasticity reported in invaded areas could be a heritage from populations in the native range.

Colonization of gastropods on subtidal reefs depends on density in adjacent habitats, not on disturbance regime

Tuya, F., Wernberg, T., Thomsen, M. S. — 2009-01-13

Habitats dominated by algal canopies are often altered by physical disturbances of varying severity, changing environmental conditions and biological processes. We used Artificial Seaweed Units (ASUs) to test whether severity of physical disturbances on algal canopies affects the post-disturbance colonization of gastropods on subtidal reefs. Specifically, we examined patterns of assemblage structure of gastropods to test the hypothesis that the extent and intensity of canopy removal affects the post-disturbance colonization of ASUs, testing the consistency of these effects among four regions encompassing a ~6° latitudinal gradient in southwestern Australia. Because adjacent habitats can act as a source of new colonists (either as drifting migrants or as a source of propagules) from the perimeter surrounding perturbed areas, we also predicted that patterns of colonization (types and total abundances of colonizers) were influenced by the available pool of individuals at the scale of reefs. Three reefs were selected within each region. On each reef, ASUs were placed in the centre of circular canopy clearings of different size (0, 3, 13 and 50 m²) and intensity (50% vs 100%), and retrieved after 3 months. Resulting assemblages occupying the ASUs were quantitatively representative of the adjacent (undisturbed), algal-associated, assemblages at the scale of reef. Within reefs, recruited assemblages largely mimicked those associated with erect red algae. However, neither disturbance size nor intensity affected the colonization patterns across reefs and regions. These results suggest that algal-associated gastropods, regardless of the prevalent mode of dispersion, are resilient to physical disturbances to canopies across broad geographical regions as long as the pool of potential colonists is maintained. A high dispersal ability of gastropods likely ensures a quick colonization of recovering algal habitats.

Shell growth, reproduction and mortality of Ovula ovum in southern Kyushu, Japan

Kawai, K. — 2009-01-13

Seasonal shell growth, reproduction and mortality of the egg cowry Ovula ovum were studied from May 2004 to October 2006 in southern Kyushu, Japan, an area at the northern margin of its geographic distribution. Rapid shell growth was observed during the period of warmer ocean temperature (May–October). Average shell growth rate of small cowries was 2.84 mm/week. Reproductive activities were observed during most of the year except during the coldest period (March–April). Egg cowries reach maturity at approximately 7 cm in shell length, and at 1 year of age. Average shell length of brooding females and copulating pairs (female and male) were 8.14 ± 0.40, 8.17 ± 0.49 and 8.08 ± 0.43 cm (mean ± SE), respectively. High mortality rates (average 67.5%) were observed from December to May. The maximum numbers of empty shells in the field (April 2005, May 2006) were seen during the period of the lowest ocean temperatures (March 24, 2005; March 7, 2006). This suggests that ocean temperature may be an important factor for egg cowry populations at the northern margins of their geographical distribution, and that O. ovum may increase fitness with rapid shell growth and early age of maturation.

Molecular properties of the partially SDS-resistant lectin from the albumen gland of Helix pomatia and demonstration of lectin-related molecules on the surface of H. pomatia haemocytes

Renwrantz, L., Marquart, A., Mock, A., Richards, E. — 2009-01-13

Lectins (agglutinins) are components of the immunobiological recognition system of vertebrates and invertebrates. The present study focused on the molecular properties of the agglutinin from the albumen gland of Helix pomatia (HPA) and on the occurrence of lectin-related molecules on the surface of H. pomatia haemocytes. According to the current model (Hammarström et al., 1972, Scandinavian Journal of Immunology, 1: 259–301), the hexameric HPA of about 79 kDa is composed of three non-covalently associated dimers (26 kDa), each consisting of two disulphide-bridged 13 kDa monomers. However, on native-gradient polyacrylamide gel electrophoresis (PAGE), we obtained high molecular weight bands representing lectin polymers. The stepwise dissociation of these was achieved by incubation with SDS at temperatures from 20 to 40°C (1 h) and at 100°C (10 min). The results obtained on SDS–PAGE included the occurrence of partially SDS-resistant hexamers of about 66 kDa, of two dimer bands of 22 and 19 kDa, and of two minor heteromonomer fractions. Complete dissociation into heteromonomers of 13 and 11 kDa was achieved by boiling the lectin (10 min) with SDS under reducing conditions. For native lectin molecules, both monomers occurred as disulphide-linked homodimers. Monomers or dimers electroeluted from an SDS–gel, reassociated to SDS-resistant oligomers upon re-electrophoresis. Finally, molecules antigenetically related to the lectin were extracted from the membrane of H. pomatia haemocytes. Anti-HPA antibodies recognized peptides with an apparent molecular weight of about 30 and 56 kDa, which were shown to represent cell-surface molecules.

Changes in gape frequency, siphon activity and thermal response in the freshwater bivalves Anodonta cygnea and Margaritifera falcata

Rodland, D. L., Schone, B. R., Baier, S., Zhang, Z., Dreyer, W., Page, N. A. — 2009-01-13

Physiologically-driven rhythms in bivalve molluscs are predicted to vary as a function of metabolic rate and temperature, in contrast to genetically predisposed biological clocks. These rhythms can be evaluated using long-term video monitoring techniques under controlled conditions in laboratory aquaria. The bivalves Anodonta cygnea and Margaritifera falcata were used to evaluate the effect of temperature on rhythms in gape and the formation of siphons at the mantle edge. Frequency and duration of shell closure vary with temperature in both species, but with different responses. Mean duration of intervals of valve closure decreases as temperature rises in both species, and is consistent with physiological limitation by increased biological oxygen demand. For A. cygnea, cumulative gape duration peaks at 25°C, with less time spent closed than at any other temperature, but increasing temperatures correspond to an increase in gape frequency with a strong increase observed at 31°C. In contrast, frequency of adduction and valve closure peak at 25°C in M. falcata, and continuous gaping is observed above 29.5°C. This physiological stress is consistent with evidence from sclerochronologically-calibrated stable isotope studies of shells, where growth breaks in many marine taxa coincide with maximum temperatures above 31°C as derived for ¹⁸O_carbonate. The results of this study suggest that these growth breaks may be due to physiological limitations in oxygen uptake and metabolic activity, rather than being a direct consequence of elevated temperature alone.

Structural analysis of the digestive gland of the queen conch Strombus gigas Linnaeus, 1758 and its intracellular parasites

Gros, O., Frenkiel, L., Aldana Aranda, D. — 2009-01-13

This study describes the structure of the digestive gland of Strombus gigas in individuals from Guadeloupe and discusses the function of its cell types and their relationship with intracellular Apicomplexa-like parasites. Three cellular types were found in the epithelium of the blind-ending tubules of the digestive gland according to histological and transmission electron microscopy (TEM) observations; these were: digestive cells, pyramidal crypt cells and vacuolated cells. Columnar digestive cells were characterized by large Alcian blue-positive granules, which have not been previously described in digestive cells of other caenogastropods. Such granules contain large quantities of proteoglycans that are exported to the stomach through the physiological destruction of the digestive cells, which undergo a holocrine secretion. Their cytoplasm appears vacuolar due to lipid extraction by solvents used for tissue preparation. Vacuolated cells also appear to be lipid-storage cells. Small triangular-shaped crypt cells, on the other hand, appear to be metabolically active as suggested by a strong positive in situ hybridization of eukaryotic ribosomes, which was confirmed by their large content of ribosomes and rough endoplasmic reticulum compared to the other cell types. These observations suggest that crypt cells may be immature cells that are involved in the replacement of eliminated digestive cells. However, their spherocrystal inclusions indicate that they may be excretory cells or calcium cells. Large brown inclusions were frequently observed in vacuolated cells; these were identified as parasitic protozoans and were present in the digestive gland of all sampled specimens. These protozoans have previously been described from a queen conch population in the San Andres Archipelago (Colombia). Several life cycle stages of the parasite were identified by scanning electron microscopy and TEM; trophozoites were characterized by their conoid-like structure, sporocysts by their thick walls, and gamonts by their thin walls. These observations suggest that this parasite completes its entire life cycle within the same host and type of tissue. Although previous investigations place this parasite within the Apicomplexa group, further investigations are necessary in order to confirm the identification of the parasite.

Ultrastructure of epidermal cilia and ciliary rootlets in Scaphopoda

Lundin, K., Schander, C., Todt, C. — 2009-01-13

Ciliary structure in Scaphopoda is hitherto unknown and may provide information useful for phylogenetic analyses. Here we describe the ultrastructure of the ciliary apparatus of multiciliated epidermal cells of four species of Scaphopoda: Antalis entalis, Antalis occidentalis, Entalina tetragona and Cadulus propinquus, revealed by transmission electron microscopy. In all studied species the cilia have long whip-like distal ends. The rootlet apparatus consists of a basal foot, a short anterior ciliary rootlet and a long vertical rootlet. In other molluscan classes, the presence of an anterior rootlet has previously only been shown in species of the Neomeniomorpha, Chaetodermomorpha and Polyplacophora, while such a rootlet is absent in Gastropoda, Bivalvia and Cephalopoda. Twin rootlets, such as present in species of lamellibranch Bivalvia and postembryonic Cephalopoda probably represent a split vertical rootlet. The discovery of an anterior rootlet in Scaphopoda shows that the presence of paired ciliary rootlets is not a synapomorphy of a clade comprising the aplacophoran Neomeniomorpha and Chaetodermomorpha and the Polyplacophora, but that it represents a plesiomorphy of the Mollusca.

Seasonal periodicity of growth and composition in valves of Diplodon chilensis patagonicus (d'Orbigny, 1835)

Soldati, A.L., Jacob, D.E., Schone, B.R., Bianchi, M.M., Hajduk, A. — 2009-01-13

Freshwater mussels of the genus Diplodon (Unionida) are common inhabitants of lakes and rivers in South America, and have slow growth and long life spans. We established the annual periodicity of incremental shell growth in Diplodon chilensis patagonicus (d'Orbigny, 1835) and calculated growth rates at different ages, using internal ring counting supported by dyeing methods and ¹⁸O isotope analyses, in two Patagonian populations (Lago Steffen and its effluent Río Manso Inferior, Argentina). Longevities of ca. 90 years (Lago Steffen) significantly extend the life spans reported in the past. Growth rates for old individuals (>30 years) from both lake and river populations average 0.16 mm per year along the axis of minimal growth. We evaluated the seasonal periodicity of minor and trace elements (Mn, Mg, Sr, Ba, Na, S) in situ by Laser Ablation ICP-MS and Electron Probe Microanalyser analyses. Line-scans in a valve from Lago Steffen show that Mn, Sr and Ba are preferentially accumulated during the summer, while higher concentrations of Mg are found in the winter bands. Metal/Ca ratios may serve as long-term archives of environmental variables, e.g. metal concentrations in water, water temperature and primary productivity. Diplodon chilensis patagonicus valves exhibit excellent characteristics to construct an accurate chronological archive with time windows of up to around a century, resolving the environmental signal annually and even seasonally.

The origin of the endemic patellogastropod limpets of the Ogasawara Islands in the northwestern Pacific

Nakano, T., Yazaki, I., Kurokawa, M., Yamaguchi, K., Kuwasawa, K. — 2009-01-13

First report of a case of occasional hermaphroditism in Polyplacophora

Scarano, A., Ituarte, C. — 2009-01-13

A conspicuous, water-resistant ink for marking terrestrial snails

Severns, P. M. — 2009-01-13

A new species of Pyropelta (Gastropoda: Pyropeltidae) from hydrothermal vents in the Okinawa Trough, southwestern Japan

Sasaki, T., Okutani, T., Fujikura, K. — 2008-10-24

A new species of the genus Pyropelta (Pyropeltidae) was collected from hydrothermal vents in the Okinawa Trough, Japan. The generic assignment is confirmed by shell, radular morphology and several anatomical characters of the animal. Comparison of shell microstructural characters with other molluscs revealed possible new diagnostic characters of Pyropelta: (1) an irregular laminate sculpture associated with multiple insertion of thin prismatic sublayers, (2) a thick myostracum attaining whole shell thickness, (3) microtubules penetrating the myostracum completely and (4) internal position of shell growth front. At species level, P. ryukyuensis n. sp. is distinguished from other Pyropelta species by eight characters of the shell, shell microstructure and radula.

Delimitation and phylogenetics of the diverse land-snail family Urocoptidae (Gastropoda: Pulmonata) based on 28S rRNA sequence data: a reunion with Cerion

Uit De Weerd, D. R. — 2008-10-24

The extreme morphological diversity in the land-snail family Urocoptidae has complicated its delimitation from other land-snail families, and has obscured its intra- and interfamilial phylogenetic relationships. Using an independent dataset of 28S rRNA DNA-sequence data, I tested morphology-based hypotheses about these relationships. These data refute the recent placement of the Australian genus Coelocion within the Urocoptidae. Instead, they provide strong support for a North American/circum-Caribbean clade, to be named Urocoptoidea (new superfamily), which consists of the families Urocoptidae and Cerionidae. In all optimal trees (maximum likelihood, maximum parsimony and Bayesian), Cerion is nested among New World Urocoptidae, rather than occupying a basal position as their sister group. Even so, the monophyly of the New World Urocoptidae could not be statistically rejected. Judging from the fossil record, the superfamily Urocoptoidea originated in the southwestern part of the North American continent, where it was widespread by the late Cretaceous. The Antillean Urocoptoidea most likely constitute three separate lineages that may have been carried eastward on the proto-Antillean island arc, which started in the late Cretaceous from a position near the SW North American landmass. Shell characters used in urocoptid classification are re-evaluated in the light of these results, and consequences for taxonomy and implications for evolutionary research are discussed.

Mate choice is not affected by mating history in the simultaneously hermaphroditic snail Lymnaea stagnalis

Koene, J. M., Loose, M. J., Wolters, L. — 2008-10-24

Mate choice based on mating history is one way to optimize the distribution of one's sperm. This is especially pertinent when donating semen is costly. Owing to sperm competition many species allocate different amounts of sperm depending on their partners' mating histories. The hermaphroditic Lymnaea stagnalis has a preference for inseminating different partners, rather than the same one twice. Moreover, virgin partners receive more sperm than nonvirgins. Here we aim to determine whether these hermaphrodites prefer to inseminate virgins. Therefore, focal animals were offered a choice between one mating partner raised in isolation and one raised in a group. For each rearing condition we also measured individual growth, onset of egg laying (waiting time) and hatching success. Of the growth parameters we found that only the asymptotic size differed, with the virgins attaining a larger size. This coincides with the delayed onset of laying selfed eggs by virgins. Selfed eggs did not differ in hatching success from outcrossed eggs. The choice experiment revealed that focal individuals mated randomly with animals raised in isolation (virgins) and raised in groups (nonvirgins). This leads us to conclude that the decisions about whether to mate with an encountered individual and how much sperm to donate to this individual are two separate processes.

Use of mollusc shells for DNA-based molecular analyses

Geist, J., Wunderlich, H., Kuehn, R. — 2008-10-24

Genetic approaches are increasingly being considered for investigations into the systematics and the conservation biology of molluscs. Here, we investigate the potential of using shell material for DNA-based analyses, using the example of endangered freshwater pearl mussels (Margaritifera margaritifera). Tissue and shells from 15 dead specimens were sampled. Their shells were split into four-quarters and re-exposed to original stream water for zero (unexposed), 1, 3 and 6 months. The influences of exposure time and resulting shell degradation, different grinding procedures and different DNA extraction methods on the quantity and quality of extractable DNA were assessed, using tissue samples as a reference. A combination of short shell-exposure time, medium grinding size and phenol–chloroform extraction procedures resulted in the most robust PCR and in lowest microsatellite genotyping errors. Amplification of nine microsatellite loci was successful in 89% of samples derived from fresh shell DNA. Genotyping errors were mostly the result of false alleles (7.8%), whereas allelic dropout only occurred at a rate of 5.7%. Shell material re-exposed to stream water for ≥1 month did not produce reliable genotyping results but amplification of mitochondrial COI was still successful. Real-time quantitative PCR of microsatellite-flanking DNA regions was shown to be an effective tool for pre-assessing DNA-quantity in shell material. These results suggest that fresh shell material may be a useful source of DNA for genetic analyses in mollusc species if the increased risk of errors compared to the use of soft tissues is adequately addressed.

Jujubinus striatus (Linnaeus, 1758) (Gastropoda:Trochidae) from a deep Zostera marina bed in southern Spain (Alboran Sea): aspects of ecology and biology

Rueda, J. L., Marina, P., Salas, C., Urra, J. — 2008-10-24

The malacofauna associated with Zostera marina beds in the Marine Protected Area ‘Acantilados de Maro-Cerro Gordo’ (southern Spain) includes a high number of species, but Jujubinus striatus is the dominant species throughout the year (dominance of 79.5% during day and 60.3% at night). The density of this trochid is maximal in the spring and summer months (up to 172.8 ± 62.4 individuals/m²) and ultrajuveniles (shell height <1 mm) occur in the eelgrass bed from February to October. The temporal dynamics of this species abundance is linked to that of the foliage of Z. marina over its annual cycle. Jujubinus striatus reproduces from at least March to November, according to a histological study of the gonads. The reproductive potential of the population is enhanced by early sexual maturity (at 2 mm size) and by the ability of a single individual to reproduce more than once a year. These reproductive features may be of importance for maintaining the J. striatus population at a high dominance level in this habitat.

Density effects of native and exotic snails on growth in juvenile apple snails Pomacea paludosa (Gastropoda: Ampullariidae): a laboratory experiment

Conner, S. L., Pomory, C. M., Darby, P. C. — 2008-10-24

Pomacea paludosa (native Florida apple snail) is found in wetlands in the southeastern United States. Pomacea insularum is an exotic apple snail which has invaded wetlands in Florida and co-occurs with P. paludosa. The effect of changes in density on growth in native juvenile snails was studied by manipulating native juvenile density, native adult density and exotic adult density in a set of laboratory experiments. Growth decreased when native juvenile densities (without adults) increased from four to eight snails per 38-l aquarium. The presence of adults of either species decreased juvenile growth and also decreased juvenile survival. One exotic adult had the equivalent effect of three to four native adults. Based on the response of native juveniles to exotic adults, populations of the native apple snail P. paludosa could be negatively impacted by expansion of the exotic snail P. insularum.

Inheritance of predominantly hidden shell colours in Macoma balthica (L.) (Bivalvia:Tellinidae)

Luttikhuizen, P. C., Drent, J. — 2008-10-24

Adults of the bivalve Macoma balthica live burrowed in mud or sand, which makes their shells invisible so that a vision-related selective advantage of colour morphs is hard to imagine. Nevertheless, this species harbours a conspicuous colour polymorphism of white, yellow, orange and red. Here we present data from laboratory-reared crosses that demonstrate a genetic basis for this colour polymorphism. The results suggest a simple model of inheritance of colour class: four alleles at a single locus displaying linear hierarchy of dominance, in the following order of increasing dominance: white < yellow < orange < red. Shell colour intensity is also shown to be a heritable trait in M. balthica. Furthermore, bicolouration may to a degree be a heritable trait, but the sample size is too small to draw any conclusions about possible inheritance mechanisms. Heritable colour variation can now, with the proposed model, be used as a genetic marker. Furthermore, the proposed model will provide the basis for further analysis of the evolutionary forces maintaining this colour polymorphism that is hidden from view for most of the life of this bivalve.

Anatomical and molecular studies reveal several cryptic species of the endemic genus Mandarina (Pulmonata: Helicoidea) in the Ogasawara Islands

Chiba, S., Davison, A. — 2008-10-24

The endemic genus Mandarina from the Ogasawara Islands in the north-western Pacific has undergone a significant adaptive radiation, and so is of interest in understanding speciation in land snails. While the majority of Mandarina species are easily recognized because underlying morphological differences in genital characters are mirrored by differences in the shell and ecology, we show here that the genus also includes several cryptic species. On the basis of anatomical characters described here, and supported by previously published phylogenies using mitochondrial rRNA sequences, we conclude that five distinct species were previously included in two nominal species: Mandarina hayatoi n. sp., and M. kaguya n. sp., both previously M. hahajimana, are a morphologically variable, allopatric/parapatric species complex on the Hahajima archipelago; M. tomiyamai n. sp. is conchologically similar to M. hirasei on Chichijima, but with distinct genital morphology. Populations of these cryptic species may have similar shells because of convergent evolution, a result of adaptation to similar arboreal lifestyle, so divergence of sexual organs must have occurred independently of habitat preference. These findings therefore support the assertion that sexual selection is an additional factor in the radiation of Mandarina.

Microanatomy, shell structre and molecular phylogeny of Leptogyra, Xyleptogyra and Leptogyropsis (Gastropoda: Neomphalida: Melanodrymiidae) from sunken wood

Hess, M., Beck, F., Gensler, H., Kano, Y., Kiel, S., Haszprunar, G. — 2008-10-24

The helicoid microgastropod genera Leptogyra, Xyleptogyra and Leptogyropsis from deep, sunken wood off New Zealand, were originally classified among the poorly defined Skeneidae (Vetigastropoda, Trochoidea) based on shell characters, external morphology and fine-structure of radulae. We investigated the microanatomy and histology of several representatives by means of serial semi-thin sectioning followed by computer-aided 3D-reconstruction, studied the shell structure, and performed phylogenetic analyses of histone (H3) and COI-sequences in order to substantiate the neomphalidan nature of these genera. The anatomical data, in particular the lack of sensory papillae, the presence of a single left kidney, left-side innervated copulatory organs, glandular gonoducts, eggs without a vitelline layer, a single pair of radular cartilages, a rectum passing beneath the heart and statocysts with a single statolith clearly exclude Leptogyra, Xyleptogyra and Leptogyropsis from the Skeneidae and from the Vetigastropoda as a whole, but strongly suggest a systematic position among the Neomphalida, where the small, helicoid genus Melanodrymia shows most similarities. This conclusion is also supported by shell structure (in particular by the presence of shell pores similar to Neomphalus), and by the molecular trees. Similar to whale falls, the sunken wood habitat might have served as an ecological bridge between the ancestral regular deep benthos and the hydrothermal vent habitat otherwise typical for Neomphalida. We argue that Neomphalida is a separate basal clade of rhipidoglossate Gastropoda.

A second species of Pyrgulopsis (Hydrobiidae) from the Missouri River basin, with molecular evidence supporting faunal origin through Pliocene stream capture across the northern continental divide

Hershler, R., Liu, H.-P., Gustafson, D. L. — 2008-10-24

The large, predominantly western North American hydrobiid gastropod genus Pyrgulopsis includes a single species from the upper Missouri River basin (MRB), P. bedfordensis, which is thought to have originated through a late Neogene transfer of drainage from the eastern Snake River Plain across the northern continental divide. Here we describe a second, morphologically distinctive congener living in the MRB, P. blainica new species; investigate the phylogenetic relationships of these two snails relative to other regional congeners using cytochrome c oxidase subunit I (COI) sequences; and evaluate whether our findings are consistent with vicariance resulting from prior stream capture across the northern continental divide. A Bayesian analysis of 39 COI sequences delineated the two MRB species as a well supported, terminal clade that is most closely related to a congener from the southern Bonneville Basin (P. anguina). Application of an available molecular clock for Pyrgulopsis suggests that the MRB clade diverged from its sister taxon 3.64 – 2.53 Ma (late Pliocene). Although these results are not consistent with the hypothesized origin of this fauna through a late Miocene drainage transfer from the upper Snake River basin, they conform to a more recent stream capture event involving truncation of southward drainage from the MRB that was previously postulated on the basis of molluscan distributions. This study provides the first molecular phylogenetic evidence that bears upon the freshwater molluscan biogeography across the northern continental divide.

The self-thinning rule applied to cultured populations in aggregate growth matrices

Filgueira, R., Peteiro, L. G., Labarta, U., Fernandez-Reiriz, M. J. — 2008-10-24