Journal of Molluscan Studies - recent issues

Embryonic and larval development of Ensis arcuatus (Jeffreys, 1865) (Bivalvia: Pharidae)

Da Costa, F., Darriba, S., Martinez-Patino, D. — 2008-04-22

The razor clam Ensis arcuatus (Jeffreys, 1865) is distributed from Norway to Spain and along the British coast, where it lives buried in sand in low intertidal and subtidal areas. This work is the first study to research the embryology and larval development of this species of razor clam, using light and scanning electron microscopy. A new method, consisting of changing water levels using tide simulations with brief dry periods, was developed to induce spawning in this species. The blastula was the first motile stage and in the gastrula stage the vitelline coat was lost. The shell field appeared in the late gastrula. The trochophore developed by about 19 h post-fertilization (hpf) (19°C). At 30 hpf the D-shaped larva showed a developed digestive system consisting of a mouth, a foregut, a digestive gland followed by an intestine and an anus. Larvae spontaneously settled after 20 days at a length of 378 µm.

Microsatellite cross-species amplification in the genus Littorina and detection of null alleles in Littorina saxatilis

Panova, M., Makinen, T., Fokin, M., Andre, C., Johannesson, K. — 2008-04-22

Microsatellite DNA is widely used as population genetic marker, but the cost of using microsatellites is high, as they usually need to be developed and optimized for each species separately. Cross-species amplification of microsatellites is therefore commonly applied to bring down the cost, but it can also involve genotyping errors. We studied cross-species amplification of microsatellites in four species of the Atlantic group of Littorina (Neritrema): L. saxatilis (Olivi, 1792), L. obtusata (Linnaeus, 1758), L. fabalis (Turton, 1825) and L. arcana Hannaford Ellis, 1978 to investigate whether markers originally developed for a more distantly related Pacific species [L. subrotundata (Carpenter, 1864)] suffered from more amplification problems than markers developed for one of the species in the Atlantic group (L. saxatilis). We also compared variation in amplification success among the species and among different regions in the NE Atlantic. Approximately half of the 12 primers developed for L. subrotundata and the seven primers developed for L. saxatilis were successfully amplified in other species of the subgenus. The success was dependent on phylogenetic distance among species within the subgenus. On the other hand, the variation in performance of the loci between geographically remote populations of the same species was as high as variation among the species. In earlier studies statistical analyses indicated that several loci showed a heterozygote deficiency due to null alleles. The presence of null alleles was confirmed by a segregation analysis of the microsatellite loci in eight half-sib families of L. saxatilis.

A review of European 'Mysella' species (Bivalvia, Montacutidae), with description of Kurtiella new genus

Gofas, S., Salas, C. — 2008-04-22

The type species of the genera Mysella Angas, 1877, Rochefortia Vélain, 1878, Rochefortula Finlay, 1927 and Altenaeum Spaink, 1972 are illustrated and discussed. A new genus Kurtiella is introduced for ‘Mysella’ bidentata (Montagu, 1803) and other European species currently placed in Mysella. These species display a unique diagnostic character state in having the cardinal platform deeply receding to house the internal ligament, along with an array of more general montacutid traits. At the species level, diagnostic characters are given for the type species K. bidentata, and for other included species K. ovata (Jeffreys, 1881), K. pellucida (Jeffreys, 1881), K. triangularis (Watson, 1897) and K. tumidula (Jeffreys, 1866), based mostly on characters of the prodissoconch and on shell outline. Montacuta simillima Smith, 1892, from St Helena, is considered a junior synonym of K. pellucida. The loss of labial palps in K. tumidula is interpreted as a further derived character, which does not conflict with the generic placement in Kurtiella.

Worth a second look: gill structure in Hemipecten forbesianus (Adams & Reeve, 1849) and taxonomic implications for the Pectinidae

Beninger, P. G., Decottignies, P. — 2008-04-22

The gill of the reef-dwelling Hemipecten forbesianus was examined using histology and scanning electron microscopy, in order to verify its reported homorhabdic state, and to provide the first detailed information on tropical pectinid gill structure. Due to the difficulty of obtaining live individuals, museum reference specimens were used for this study. The gill is heterorhabdic, and presents several notable differences compared to the larger, temperate species studied to date: (1) the small number of ordinary filaments per plica (probably associated with the very small size of these specimens), (2) the outer demibranch is approximately 15% shorter than the inner demibranch, (3) several characteristics which confer gill cohesion in other pectinid gills are absent and (4) the principal filaments are devoid of mucocytes, such that particle transport of positively-selected particles must be entirely effected in water. The apparent universality of the heterorhabdic condition within the Pectinidae leads us to recommend its use as a reliable soft-body taxonomic character at the family level. The anatomical differences between the gill of H. forbesianus and that of the larger, temperate species call for further comparison with both large and small, temperate and tropical species, in order to elucidate the effects of size and habitat on gill structure in this family.

Systematic revision of Jorunna Bergh, 1876 (Nudibranchia: Discodorididae) with a morphological phylogenetic analysis

Camacho-Garcia, Y. E., Gosliner, T. M. — 2008-04-22

The genus Jorunna is characterized by a dorsum covered with caryophyllidia, a prostate with two sections, a penis usually unarmed but occasionally armed with hooks, a copulatory spine, the presence of an accessory gland and a labial cuticle smooth or armed with jaw elements. The examination of 216 non-type specimens, 30 types, and a review of the literature show that there are 16 valid species of the genus Jorunna: J. tomentosa (Cuvier, 1804); J. funebris (Kelaart, 1859); J. pantherinaAngas, 1864; J. rubescens (Bergh, 1876); J. labialis (Eliot, 1908); J. parva (Baba, 1938); J. spazzola (Marcus, 1955); J. hartleyi (Burn, 1958); J. alisonaeMarcus, 1976; J. lemchei (Marcus, 1976); J. evansi (Eliot, 1906); J. pardusBehrens & Henderson, 1981; J.ramicolaMiller, 1996 and J. onubensis Cervera, García-Gómez & García, 1986. In addition, two new species from the Eastern Pacific are described: J. osae n. sp. and J. tempisquensis n. sp. We propose two new combinations: Jorunna parva and J. evansi. New records for the genus Jorunna are provided from Italy, Algeria, Seychelles, Madagascar, Thailand, Marshall Islands, New Caledonia, Île de la Réunion, Sudan, Papua New Guinea, Indonesia, Panama, Costa Rica, Bahamas, and Southern Mexico. We present the first preliminary phylogenetic analysis of this cryptobranch dorid genus, based on morphological anatomical data, and discuss the biogeography and evolution of several characters in this group. The phylogeny supports the hypothesis that the genus Jorunna is a monophyletic group and shows that Kentrodoris is nested within it.

Variability in the sculpture of the shell aperture of Ruthenica filograna (Rossmassler, 1836) (Gastropoda: Clausiliidae) in specimens from natural populations and from laboratory breeding

Szybiak, K., Lesniewska, M. — 2008-04-22

An analysis of variability in the sculpture of shell apertures was carried out for 1,087 specimens of Ruthenica filograna from 33 localities and for 20 laboratory-bred individuals reared from parents from a single locality. Nine patterns of aperture sculpture were distinguished. There are usually two kinds of sculpture: with one plica in the aperture being an extension of the inferior lamella, and without plicae in the aperture. Sporadically, the subcolumellar lamella may be connected with the lip of the aperture by a plica. Additional plicae occur in the aperture only rarely. All populations examined showed variations in the number and arrangement of plicae. The coefficient of variation in the number of plicae in the shell aperture ranged from 32.6% to 121.8% within localities. No consistent relationship was found between the geographical location and the shell sculpture pattern. Specimens bred in the laboratory developed shell apertures with a variety of sculptural patterns, including one present neither in the parents, nor in the population from which it came. This characteristic is probably phenotypically plastic. It cannot be used for taxonomic purposes, and it is suggested that great caution is needed before using similar characters in other species.

Population characteristics and planktonic larval stage of the New Zealand screwshell Maoricolpus roseus

Probst, T. A., Crawford, C. M. — 2008-04-22

Maoricolpus roseus is believed to have been introduced into Tasmania in the 1920s. Despite its wide distribution, dense populations and being considered successful in colonizing and altering several habitats, details of its reproduction and life cycle are not known. Specimens collected from the D'Entrecasteaux Channel (SE Tasmania) over 2 years showed sexual dimorphism with females relatively larger than males. A 1:1 sex ratio was observed and females were found carrying encapsulated larvae throughout consecutive austral summer seasons (September or October till February), with up to 70% of females carrying larvae. Larvae released from egg capsules were planktonic, all relatively well developed, and fed on microalgae, indicating that the species has planktotrophic development, and suggesting high potential for dispersal. This information is important for the development of management strategies to control this invasive species.

Molecular evidence of the evolutionary origin of a Bonin Islands endemic, Stenomelania boninensis

Miura, O., Mori, H., Nakai, S., Satake, K., Sasaki, T., Chiba, S. — 2008-04-22

Histochemical localization of NADPH-diaphorase-positive elements in the enteric nervous system of bivalve molluscs

Pimenova, E. A. — 2008-02-11

Using a nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry, localization and morphology of putative nitric oxide synthase-containing elements were studied in the intestine of the following bivalves: Ruditapes philippinarum, Callithaca adamsi, Mercenaria stimpsoni (Veneridae), Corbicula japonica (Corbiculidae), Nodularia vladivostokensis and Cristaria tuberculata (Unionidae). NADPH-d-positive nerve cells and plexuses were found in the intestine of all species studied. Labelled diformazan bipolar nerve cells were present in the epithelium of the intestinal groove and typhlosole of the anterior midgut, the midgut proper, and the hindgut. Their apical process extended towards the gut lumen, whereas the basal one was connected with the basiepithelial NADPH-d-positive nerve plexus. In the typhlosole of N. vladivostokensis, these cells constituted up to 2.68% of the total number of epithelial cells. The bivalve species studied exhibit a similar distribution pattern of NADPH-d-positive cells, which lie separately or form small groups of two to three in the basal part of the epithelium. Basiepithelial NADPH-d-positive plexus was connected by separate fibres with subepithelial NADPH-d-positive nerve plexus. Both the plexuses were moderately developed in all intestinal regions in the majority of the species examined.

Origin of a metal-binding protein in serum of Mytilus edulis

Renwrantz, L., Werner, I. — 2008-02-11

The most abundant humoral protein of the haemolymph of Mytilus edulis is known to bind a variety of heavy metals (Renwrantz et al., 1998 Comp. Biochem. Physiol. A, 121: 175–180). This serum protein band 1 (SPB1) was isolated from Mytilus serum by a two-step purification procedure. For the purified protein a molecular weight of 34 kDa was estimated under denaturing conditions and of 37 kDa in its reduced form. After blotting of Mytilus serum onto a nitrocellulose membrane, Cu-binding by SPB1 was visualized. Furthermore, indications were obtained of Ca-binding properties of SPB1 and of some bands postulated to be SPB1-oligomers. Formation of dimers was confirmed by their reaction with SPB1-specific antibodies. On immunoblots, anti-SPB1 detected the metal-binding protein in postnuclear haemocyte extracts. After further fractionation of the cell homogenate by sucrose gradient centrifugation, the indicator antibodies recognized SPB1 in the cytosol, as a component of the plasma membrane and in the fraction of granules which was assumed to include secretory vesicles. Investigation of the supernatant from a 24 h haemocyte culture indicated release of the metal-binding protein by blood-cells. Incubations of different haemocyte monolayers on slides with anti-SPB1 indicated expression of SPB1 in amounts of 55% to almost 100% of the cells, whereby the intensity of antibody-staining varied between individual haemocytes. Intensity was independent of cell type as density gradient separation of haemocytes into basophilic and eosinophilic granulocytes resulted in similar staining patterns in both groups. Thus, all granulocytes seemed to be able to produce SPB1 with a varying degree of activity indicating a hitherto unknown regulation system.

Embryonic shell formation in the snail Biomphalaria glabrata: a comparison between scanning electron microscopy (SEM) and synchrotron radiation micro computer tomography (SR{micro}CT)

Marxen, J. C., Prymak, O., Beckmann, F., Neues, F., Epple, M. — 2008-02-11

Embryos of different developmental stages and newly hatched juveniles of the freshwater snail Biomphalaria glabrata were investigated by synchrotron radiation micro computer tomography (SRµCT). Because this method is sensitive for objects with a high X-ray density, it is ideally suited to study mineralized tissues without the need for dissection of the sample, i.e. removal of the soft tissue. This is a clear advantage over scanning electron microscopy (SEM). However, the resolution is inferior to SEM (about 1–2 µm compared to a few nm). After the measurement, computer-processed handling (virtual turning, cutting and measuring) of the object is possible. The development of the calcified shell in embryos before hatching (age 60, 72, 96 and 120 h after oviposition) was investigated and both methods were compared. While it was not possible to find a calcified shell in 60 h old embryos, the shell in 72 h old embryos was almost fully mineralized. By SRµCT, the weight of the calcified shell was estimated to 0.64, 9.59 and 30.3 µg for embryos of 72, 96 and 120 h. All juvenile snails, of 5 days and 4 weeks after hatching, contained concretions in the stomach, mostly consisting of calcium phosphate.

Toxoglossan gastropods of the subfamily Crassispirinae (Turridae) lacking a radula, and a discussion of the status of the subfamily Zemaciinae

Fedosov, A., Kantor, Y. — 2008-02-11

Two new species of Horaiclavus, lacking radula, venom gland and proboscis, are described. The genus is placed in the subfamily Crassispirinae (Turridae). Both species possess a peculiar foregut structure, the muscular rhynchodaeal outgrowth situated in the rhynchocoel. The possible function of the rhynchodaeal outgrowth is discussed. Other studied species of Horaiclavus possess a radula of a typical ‘crassispirine’ type but lack the outgrowth. The anatomy of the foregut of the new species is superficially similar to that of Zemacies excelsa (Turridae: Zemaciinae), which also possesses an additional structure of the rhynchocoel, namely the ‘pyriform gland’. Conchologically, there is no resemblance between Zemacies and Horaiclavus and it is concluded that similar foregut arrangement appeared independently in both lineages. A new monotypic subfamily Zemaciinae was erected mostly on the basis of the unique foregut arrangement of Zemacies excelsa. We express doubts concerning the importance of these characters in establishing a new taxon of subfamilial rank and therefore the validity of the subfamily Zemaciinae.

The composition and richness of Danubian floodplain forest land snail faunas in relation to forest type and flood frequency

Cejka, T., Horsak, M., Nemethova, D. — 2008-02-11

The species richness and composition of land snail assemblages in 42 floodplain forest sites along the Danube River in Slovakia were studied to find the main ecological gradients responsible for the variation in the faunas. We found just one, but steep, ecological gradient influencing the variation of snail species composition among different floodplain forest types, reflected in the first detrended correspondence analysis axis, which explained 29.6% of total variation. Site scores on this axis were significantly correlated with site humidity (r_s=–0.868; P<0.001). Significant loading on the first axis was also found for flood frequency and several vegetation descriptors. Species composition mainly reflected differences between sites without floods and the others. Species richness as well as total abundances of live individuals were not significantly controlled by any explanatory variable, although some trends could be discerned. Considering vegetation classification, substantial differences were observed between wet softwood floodplain forests and the remaining types, drier softwood forests and different types of hardwood forests, which were impossible to distinguish based on land snail assemblages. The results are discussed in relation to earlier descriptive studies, and in terms of the conservation of these threatened habitats.

Juvenile snails, adult appetites: contrasting resource consumption between two species of applesnails (Pomacea)

2008-02-11

Research on aquatic snails usually examines consumption of periphyton, but emergence of large, invasive aquatic snails that prefer macrophytes has necessitated a new understanding about snail herbivory. Ample research exists detailing invasive potential of certain species of applesnails, such as Pomacea canaliculata, to successfully invade aquatic ecosystems. However, very few studies examine differences in resource utilization between different size-classes within species, or between closely-related species. To quantify these potential differences, we compared per mass resource consumption at two life history stages by P. canaliculata and a lesser-known species recently identified in Texas (USA), Pomacea insularum. We presented adult and juvenile snails with whole and reconstituted forms of Lactuca sativa longifolia (romaine lettuce), Myriophyllum spp. (watermilfoil), and Eichhornia crassipes (water hyacinth). In addition, we added chemical extracts to reconstituted watermilfoil and water hyacinth to test if extracts deterred consumption. Addition of periphyton to reconstituted watermilfoil allowed us to examine supplementary structure and chemistry. Juveniles seemed to prefer reconstituted resources. All snails, regardless of life-history stage, avoided water hyacinth in either form. Chemical extracts from both water hyacinth and watermilfoil deterred consumption by all snails. When presented with reconstituted watermilfoil containing additional periphyton, juvenile P. insularum consumed more resource with additional periphyton. In contrast, periphyton presence did not produce a noticeable effect on P. canaliculata consumption. Overall, juveniles of both species consumed considerably more by mass than their respective adult counterparts. Through increased numbers and difficult detection, juvenile applesnails could feasibly consume a greater proportion of plant biomass than adult applesnails and this may partially underlie the success of global applesnail invasions.

Suspension feeding and kleptoparasitism within the genus Trichotropis (Gastropoda: Capulidae)

Iyengar, E. V. — 2008-02-11

The marine gastropod Trichotropis cancellata is a facultative kleptoparasite, either suspension feeding or parasitically stealing food from tube-dwelling polychaete worms. To determine whether conclusions drawn from long-term studies in the San Juan Islands, Washington, about the relative importance of suspension feeding and kleptoparasitism can be applied generally to T. cancellata across its biogeographic range, I expanded earlier studies to Alaska and British Columbia. Kleptoparasitism is pervasive throughout the range of T. cancellata, occurring with equal frequency throughout the areas studied. The average density and size of worm hosts are relatively constant across this range. Snail and worm densities are not significantly correlated at the larger scale of site (averaged over nearby sampling locations clustered around a city), but are correlated at the smaller local scale (within a sampling location). Larger worms do not support more snails. The abundance of uninfected worm hosts is usually not limiting, except potentially in some sampling locations in southwest Alaska where the use of a novel host (a holothurian) may be the result of low densities of uninfected worms. Additionally, I documented the feeding behaviours of other trichotropid species in these regions. Trichotropis conica is the second confirmed kleptoparasite within the genus Trichotropis, with kleptoparasitism as frequent in this species as in T. cancellata. Like T. cancellata, all sizes observed of T. conica are kleptoparasites. On the other hand, Trichotropis insignis is an obligate suspension feeder. Further studies are needed to determine exactly how many times this behaviour has arisen and been lost in Capulidae and related families.

Morphological and genetic description of Octopus insularis, a new cryptic species in the Octopus vulgaris complex (Cephalopoda: Octopodidae) from the tropical southwestern Atlantic

Leite, T. S., Haimovici, M., Molina, W., Warnke, K. — 2008-02-11

A medium-sized Octopus species is described based on material collected in shallow equatorial waters around the oceanic islands of Fernando de Noronha Archipelago, Rocas Atoll, St Peter and St Paul Archipelago and the mainland of northeastern Brazil. The new species, Octopus insularis, is described morphologically, and also characterized by the large mitochondrial subunit ribosomal RNA gene (mt 16S rDNA). The new species has relatively short and stout arms, rugose reddish brown skin in preserved specimens, 8 to 11 gill lamellae on the outer demibranchs, small ligula, characteristic symmetrical radula, spermatophore and beak, small eggs and high fecundity (213,000 oocytes under 1.5 mm diameter). The habitats and skin patterns of living animals are briefly described. The new species differs both morphologically and genetically from Octopus vulgaris in the Mediterranean, Venezuela and southern Brazil.

Do mussel patches provide a refuge for algae from grazing gastropods?

O'Connor, N. E., Crowe, T. P. — 2008-02-11

On rocky shores, cover of macroalgae is often greater growing epibiotically on mussels compared to algae growing directly attached to rock. A survey of two shores on the east coast of Ireland confirmed that mussel beds contained greater percentage algal cover and more diverse algal assemblages compared to those on rock. The reasons for this difference are not clear. It has been suggested that mussel beds provide a refuge for algae from grazing gastropods. Surprisingly, we found no evidence to support this. Using wax discs, gastropod grazing patterns were found to be similar within the mussel beds as on rock. The mussel beds do not appear to provide a refuge for algae from grazing activity at this scale and we suggest other possible mechanisms for the prevalence of epibiotic algal cover on mussels. Intertidal grazers may in fact affect the epibiotic algae on mussels and thereby affect indirectly the persistence of mussel beds.

Bronze Age shipwreck snails from Turkey: first direct evidence for oversea carriage of land snails in antiquity

Welter-Schultes, F. W. — 2008-02-11

Thirty-six shells of terrestrial gastropods were discovered in underwater archaeological excavations of a Late Bronze Age (3,300 years BP) shipwreck at Uluburun, southern Turkey. Four shells were not related to the wreck and belonged to local species from the nearby coast. The other 32 specimens were accidentally transported with the merchant ship, which had sunk when sailing in a counterclockwise route from the Syro-Palestinian coast via Cyprus to the Aegean and then to Egypt. The Near Eastern endemic Xerocrassa langloisiana and the common eastern Mediterranean synanthrope Xeropicta krynickii were found in amphoras originally containing terebinth resin, destined for Egypt. The combined ranges of the two species and the morphological record point to a narrow area near the Dead Sea, more than 50 km distant from the Mediterranean coast, as the harvesting locality of the resin. A second group of land snails, partly determined as Xp. krynickii, must have been on board the vessel under different circumstances, attached to spiny bushes used to cushion the heavy freight and to prevent the planks from being damaged. The finds provide direct evidence that land snails have been carried on ships for more than 3,000 years, and underline assumptions that human-based oversea dispersal of anthropochorous species in the Mediterranean has occurred since antiquity. The results also show how much can be done if we possess a detailed faunistic knowledge of species distributions and shell morphology.

Environmental and physiological controls on shell microgrowth pattern of Ruditapes philippinarum (Bivalvia: Veneridae) from Japan

Kanazawa, T., Sato, S. — 2008-02-11

The reproductive cycle and shell microgrowth patterns of the venerid bivalve Ruditapes philippinarum from Matsukawa-ura, a small inlet facing the Pacific Ocean, northeastern Japan were examined. Histological examination of the gonads revealed that spawning in this species occurred twice in 2005, once between late June and early August and the other between late September and early October. Comparison of the shell microgrowth patterns with the developmental stages of the gonad in each individual revealed that in spawning individuals (mature and spawning stages), the mean lunar-day growth rates were significantly smaller than those in individuals which were not in spawning condition (spent, recovery and growing stages). In non-spawning individuals, the mean lunar-day growth rates were positively correlated with seawater temperature up to 20°C. However, in spawning individuals, no correlation was observed between shell growth and seawater temperatures >16°C. These facts suggest that physiological stress during reproduction has a negative influence on shell growth and results in spawning breaks. The present study indicate that spawning breaks can be used to identify the timing of sexual maturity and to count the number of spawning events occurring per year in extant and fossil bivalves.

The ecology and life cycle of a population of Modiolarca tumida (Hanley, 1843) (Bivalvia: Mytilidae) of the coast off north-eastern England

Bodger, P.M., Allen, J.A. — 2008-02-11

The life history of a population of Modiolarca tumida occurring off the Northumberland coast is described. Modiolarca tumida lives primarily in the tests of ascidians. On settlement the young spat seek an ascidian host, climb close to the inhalent and exhalent apertures of the host and there wrap the test around themselves using the byssus. Initially, there is a preference for Ascidiella scabra as the host species but, with increasing size, Modiolarca is more and more often found in Polycarpa pomaria. While numbers per ascidian vary, usually <5 occur in each host. However, immediately following settlement very occasionally 100+ have been recorded. Modiolarca tumida is relatively short-lived, with few living longer than two years. Spawning occurs at the end of July and August at the end of its first year of life and at the same time in subsequent years in the case of the minority that survive.

Review of the systematics and global diversity of freshwater mussel species (Bivalvia: Unionoida)

Graf, D. L., Cummings, K. S. — 2007-11-20

Freshwater mussels (Bivalvia: Unionoida) are interesting because of their unique life cycles, global aggregate distribution and ancient origin. They are also of practical importance due to their worldwide, imperiled status. Of utmost utility for their continued study are a modern assessment of global and regional species diversity and a natural classification that reflects phylogenetic patterns. The freshwater malacological community has taken steps toward satisfying the latter of these requirements, but a consensus census of mussel species has not been published since Fritz Haas's revisions of the late 1960s. We set out to describe the species-level diversity of the Unionoida by reviewing the secondary literature and developing a comprehensive taxonomic database. Each valid species was assigned to one or more geographical regions (i.e. Nearctica, Neotropica, Afrotropica, Palearctica, Indotropica and Australasia) and one or more subregions, and each valid genus was assigned to the lowest possible level in a classification derived from our own, recent phylogenetic analyses. Based upon a consensus of numerous regional works, our global estimate of freshwater mussel diversity is 840 species. Regional diversity was determined as follows: Nearctica: 302 spp., Neotropica: 172, Afrotropica: 85, Palearctica: 45, Indotropica: 219 and Australasia: 33. The largest family is the Unionidae, with 674 species. However, the classification of that taxon is currently in flux, and many genera (corresponding to 225 spp.) were assigned to incertae sedis geographical assemblages. Diversity patterns are discussed, and it is suggested that reevaluation of these faunas with modern methods will likely increase recognized species diversity, especially on the southern continents. Our checklist and classification of freshwater mussel species is included as an appendix and mirrored on the MUSSEL Project Web Site (http://www.mussel-project.net/).

Pronounced karyological divergence of the North American congeners Sphaerium rhomboideum and S. occidentale (Bivalvia: Veneroida: Sphaeriidae)

Petkeviciute, R., Staneviciute, G., Stunzenas, V., Lee, T., O Foighil, D. — 2007-11-20

Chromosome sets of two North American sphaeriid species, Sphaerium rhomboideum Say, 1822 and S. occidentale Lewis, 1856, were studied using conventional Giemsa staining and karyometric analysis. Pronounced karyological divergence of congeners was revealed. The diploid number of 2n = 44 was reported for S. rhomboideum and this is the first record of a diploid species in the highly polychromosomic Nearctic sphaeriid fauna. The karyotype was characterized by medium-sized and small chromosomes, which decreased in size gradually from 5.77 to 1.9 µm. Biarmed chromosomes with medially and submedially located centromeres predominated, but six pairs of subtelo-telocentric elements were also observed in the karyotype. The estimated mitotic chromosome number for S. occidentale ranges from 189 to 213, but most of the cells examined contained about 204–209 chromosomes. A first attempt to karyotype a polyploid sphaeriid was made. It was revealed that the comparatively large and middle-sized chromosomes could be grouped in four, so the karyotype presumably evolved through tetraploidization. The small chromosomes formed the large fraction, about 137. Due to their similar and indistinct morphologies, it was impossible to arrange them into subgroups with confidence. Revealed karyological characteristics are discussed with reference to the existing phylogenetic interpretations of the evolutionary history of the Sphaeriinae.

Discovery of introduced and cryptogenic cochliopid gastropods in the San Francisco Estuary, California

Hershler, R., Davis, C. L., Kitting, C. L., Liu, H.-P. — 2007-11-20

We report the first discovery in the San Francisco Estuary (‘Estuary’) of two cochliopid gastropods, Littoridinops monroensis and Tryonia porrecta. These identifications were based on morphological criteria and supported by analysis of mitochondrial DNA (cytochrome c oxidase subunit I, COI) sequence data. We also report the first discovery of males in parthenogenetic T. porrecta. The new records represent large range extensions for both of these North American species, which were previously recorded from predominantly brackish habitats along the western Atlantic-Gulf Coast (L. monroensis) and thermal springs in the Great Basin and lower Colorado River region (T. porrecta). The COI haplotype observed in Estuary specimens of L. monroensis differed from those detected in two western Atlantic populations by only 1–3 bp, suggesting recent divergence which is not consistent with the separation of these two areas by imposing terrestrial barriers since at least the Pliocene. We suggest that L. monroensis was recently introduced to the Estuary by transoceanic shipping, adding to the large exotic biota that has invaded this highly disturbed ecosystem. The COI haplotype observed in Estuary specimens of T. porrecta is closely similar to haplotypes detected in Nevada and Utah populations and highly divergent relative to the single haplotype observed in other California populations. The implications of these findings for the status of T. porrecta in the Estuary are unclear, because the native range of this parthenogen has not been established and its scattered distribution in the West may be attributable to natural dispersal across land (on birds) and/or anthropogenic spread. Although we suggest treating T. porrecta as cryptogenic in the Estuary, a native status may be suggested by independent (subfossil) evidence that this snail was locally present prior to establishment of the area as a major centre of human population and commerce in the 1850s.

Predation of cockles (Cerastoderma edule) by the whelk (Buccinum undatum) under laboratory conditions

Scolding, J.W.S., Richardson, C.A., Luckenbach, M.J. — 2007-11-20

The feeding rate and behaviour of whelks (Buccinum undatum) offered cockles (Cerastoderma edule) in laboratory experiments were examined. When presented with cockles in a range of sizes (10–40 mm), 14 B. undatum (34.6–88.3 mm), held individually in aquaria, consumed a wide size range of cockles. Small whelks (<40 mm) consumed cockles (<23 mm), whereas large whelks, (>60 mm) ate a greater number of larger cockles (>30 mm) and a wider size range of cockles (12–40 mm) than smaller whelks. The majority (90%) of the shells of the predated cockles were undamaged and the few (<10%) that were damaged showed only slight abrasions to the anterior and posterior shell margin. Filmed observations of B. undatum feeding on C. edule showed a method of attack that has not previously been reported and involved the use of the whelk's foot to asphyxiate the cockle or to pull the shell valves apart. No filmed evidence was found for the previously reported shell ‘wedging’ technique for prising open the closed shell valves of C. edule, although 10% of the shells of consumed cockles in feeding experiments had damaged shell margins.

Computer-based 3-dimensional reconstruction of major organ systems of a new aeolid nudibranch subspecies, Flabellina engeli lucianae, from Brazil (Gastropoda: Opisthobranchia)

DaCosta, S., Cunha, C. M., Simone, L. R.L., Schrodl, M. — 2007-11-20

Obtaining accurate and comprehensive anatomical information from small opisthobranch specimens has been a major problem. Computer-based 3-dimensional reconstruction from serial histological slides applying AMIRA (TGS Graphics) software is shown to be an efficient and fully reproducible way to analyse tiny and complex organ systems in their true relative positions and proportions; this method is herein applied to nudibranchs for the first time. We used Flabellina engeli lucianae n. subsp., a small aeolid (up to 8 mm body preserved length) from subtropical southern Brazil, to illustrate all major organ systems including nervous systems, and discuss them comparatively. Flabellina engeli lucianae differs externally from congeners by having a translucent body with opaque white and iridescent blue spots, orange ceratal bands, and by the special branching of cerata forming distinct groups on common peduncles. External and internal differences from the apparently geographically and hydrographically separated Caribbean specimens of F. engeli engeli Marcus & Marcus, 1968 are discussed in detail.

Structure and function of haemocytes in two marine gastropods, Megathura crenulata and Aplysia californica

Martin, G. G., Oakes, C. T., Tousignant, H. R., Crabtree, H., Yamakawa, R. — 2007-11-20

Aplysia californica is an important mollusc for neurobiological research and Megathura crenulata is becoming valuable as the source of keyhole limpet haemocyanin (KLH) which shows promise in treating cancer, allergy and immunosuppression. The culture of these animals provides opportunities to assess their physiological responses to stress and disease. Molluscan haemocytes are known to be involved in a variety of physiological responses, yet the haemocytes of this opisthobranch and vetigastropod have not been characterized. The purpose of this study is to describe the morphology of these cells and summarize their functions based on a suite of assays previously developed on other species of molluscs. Using morphology, differential centrifugation and staining reactions, we identify a single type of circulating haemocyte in the blood of both animals. All haemocytes lack granules and contain glycogen and vesicles that react as lysosomes. In A. californica, three to four wing-like lamellipodia extend from the ovoid cell body, whereas in M. crenulata haemocytes are simple ovoid cells. The haemocytes are actively phagocytic and rates of phagocytosis are higher when the assays are performed in the presence of plasma, relative to tests with washed cells. When haemocytes engulf yeast, peroxidase and superoxides are produced. Phenoloxidase activity was not detected. When blood is removed from these molluscs, the plasma does not clot and the haemocytes rapidly adhere to one another in suspension, or settle on substrates, migrate and form nodules. Cell spreading and aggregation involves microfilaments and microtubules, and can be inhibited by EDTA, cytochalasin B, caffeine and, to a lesser extent, RGD and colchicine. All cells show immunoreactivity against a polyclonal antibody to ACTH which is consistent with previous studies suggesting molluscan haemocytes contain molecules similar to those involved with vertebrate stress responses. These results should be useful in future studies evaluating the physiological status of these animals in the wild and in culture.

Phylogeography of the Wabash pigtoe, Fusconaia flava (Rafinesque, 1820) (Bivalvia: Unionidae)

Burdick, R. C., White, M. M. — 2007-11-20

Reconstructing the phylogeographic patterns of widely distributed and common freshwater mussel species (Bivalvia: Unionidae) may provide insight into unionid evolution and speciation. The Wabash pigtoe, Fusconaia flava, is currently recognized as a single, polytypic species that is widely distributed and common throughout the Mississippi River drainage and parts of the Canadian Interior, Great Lakes and Gulf Coast drainages. Sequence analysis of the mitochondrial COI gene revealed two divergent (3.43%) clades. Clade A consisted of specimens located throughout the upper and lower Mississippi River drainage and in the Red River (Canada) and Lake Erie drainages and all F. cerina specimens. All haplotypes within clade A differed by three (0.55%) or fewer nucleotide substitutions from the most widely distributed and abundant haplotype, F1. Clade B, consisting of specimens located in the far western portion of the species' range, may comprise an undescribed species. There was no evidence of genetic differentiation among F. flava inhabiting headwater and intermediate-sized river localities of the Muskingum River system and large river localities of the nearby Ohio River. The divergence among F. flava haplotypes comprising clade A (0.18–1.10%) was similar to the divergence between the F. cerina haplotypes and the F. flava haplotypes comprising clade A (0–1.10%). This study illustrates the importance of accessing genetic diversity across the distribution of a polytypic species. Additional analyses based on a combination of morphology and genetics are needed to determine the taxonomic status of clade B and to strengthen our understanding of the relationship between F. flava and F. cerina.

Experimental deep-sea deployments reveal diverse Northeast Pacific wood-boring bivalves of Xylophagainae (Myoida: Pholadidae)

Voight, J. R. — 2007-11-20

Only a single species of deep-sea wood boring bivalve has been known off the forested northwest coast of North America, although the Xylophagainae are so diverse in other areas that up to five species occur in a given length of wood. To determine whether additional species were present in the Northeast Pacific and if so, how they coexist, lengths of wood were experimentally deployed on heavily sedimented sites on the Cascadia Basin and Escanaba Trough, non-hydrothermally active basalt on Gorda Ridge and Axial Volcano, and an isolated sediment pond within the axis of Juan de Fuca Ridge, at depths of between 1,530 and 3,232 m. All locations were between 41°and 48°N, at least 240 km off the North American coast. Six previously unknown species, Xylophaga corona n. sp., X. zierenbergi n. sp., X. heterosiphon n. sp., X. oregona n. sp., X. microchira n. sp. and Xylopholas crooki n. sp., were collected and are described here. Dominant species differed in recoveries made after 10 and 24 months at Juan de Fuca Ridge and Cascadia Basin localities. Xylophaga microchira n. sp. dominated four of five deployments recovered within 12 months, but its abundance declined by 24 months, being largely replaced on Juan de Fuca Ridge by X. oregona n. sp., a species known only from this Ridge and from an incidental collection on the Nootka Fracture Zone. At Cascadia Basin sites, the abundances of X. heterosiphon n. sp. and of what are likely to be predatory polyclad flatworms increased as that of X. microchira n. sp. declined. Xylophaga microchira n. sp. is hypothesized to be specialized for early colonization, but to be competitively inferior to X. oregona n. sp., and more vulnerable to predators than X. heterosiphon n. sp. The dominance of competitively superior and more predator-resistant species in older deployments argues that biotic interactions contribute to coexistence of multiple species of wood-borers despite direct competition among them.

Mapping of ribosomal DNA and (TTAGGG)n telomeric sequence by FISH in the bivalve Patinopecten yessoensis (Jay, 1857)

Huang, X., Hu, X., Hu, J., Zhang, L., Wang, S., Lu, W., Bao, Z. — 2007-11-20

The chromosome set of Patinopecten yessoensis (Jay, 1857) was characterized using Giemsa staining, DAPI staining and fluorescence in situ hybridization (FISH) with three repetitive DNA probes [18S–28S rDNA, 5S rDNA and telomeric (TTAGGG)_n]. DAPI staining showed that AT-rich regions were located on the centromere of almost all chromosomes and interstitial banding was not observed. FISH showed that 18S–28S rDNA spread over the short arms of two subtelocentric chromosome pairs and 5S rDNA was located on the long arm of one subtelocentric chromosome pair. Sequential FISH demonstrated that 18S–28S and 5S rDNA were located on different chromosomes. FISH also showed that the vertebrate telomeric sequence (TTAGGG)_n was located on both ends of each chromosome and no interstitial signals were detected. Sequential 18S–28S rDNA and (TTAGGG)_n FISH indicated that repeated units of the two multicopy families were closely associated on the same chromosome pair.

Molecular phylogeny of coleoid cephalopods (Mollusca: Cephalopoda) inferred from three mitochondrial and six nuclear loci: a comparison of alignment, implied alignment and analysis methods

Strugnell, J., Nishiguchi, M. K. — 2007-11-20

Recent molecular studies investigating higher-level phylogenetics of coleoid cephalopods (octopuses, squids and cuttlefishes) have produced conflicting results. A wide range of sequence alignment and analysis methods are used in cephalopod phylogenetic studies. The present study investigated the effect of commonly used alignment and analysis methods on higher-level cephalopod phylogenetics. Two sequence homology methods: (1) eye alignment, (2) implied alignment, and three analysis methods: (1) parsimony, (2) maximum likelihood, (3) Bayesian methodologies, were employed on the longest sequence dataset available for the coleoid cephalopods, comprising three mitochondrial and six nuclear loci. The data were also tested for base composition heterogeneity, which was detected in three genes and resolved using RY coding. The Octopoda, Argonautoidea, Oegopsida and Ommastrephidae are monophyletic in the phylogenies resulting from each of the alignment and analysis combinations. Furthermore, the Bathyteuthidae are the sister taxon of the Oegopsida in each case. However many relationships within the Coleoidea differed depending upon the alignment and analysis method used. This study demonstrates how differences in alignment and analysis methods commonly used in cephalopod phylogenetics can lead to different, but often highly supported, relationships.

Molecular phylogeny of the helicoid land snails (Pulmonata: Stylommatophora: Helicoidea), with special emphasis on the Camaenidae

Wade, C. M., Hudelot, C., Davison, A., Naggs, F., Mordan, P. B. — 2007-11-20

Safe and legal shipment of tissue samples: does it affect DNA quality?

Williams, S.T. — 2007-11-20