http://mollus.oxfordjournals.org Journal of Molluscan Studies - RSS feed of articles 1464-3766 Journal of Molluscan Studies 0260-1230 http://mollus.oxfordjournals.org/cgi/content/short/eyp034v1?rss=1 Histology and electron microscopy were used to describe and compare the structure of the dorso-lateral pedal defensive glands of three species of marine Basommatophora, Siphonaria capensis, S. serrata and S. gigas. All three species possessed multicellular glands, but these were largest and most abundant in S. capensis. In S. capensis and S. serrata, defensive glands were composed of two types (type I and II) of large secretory cells filled with product and some irregularly shaped support cells that surrounded a central lumen. The product of both cell types was produced by organelles confined to the bases of the cells. The entire gland was surrounded by a well-developed layer of smooth muscle and collagen. Type I cells stained positively for neutral and sulphated mucins, and observed with transmission electron microscope (TEM) the product had a reticulate appearance. By contrast type II gland cells stained positively for acidic mucins and the secretory product was formed as large granular vesicles. The products from both types of cell, which appeared to be secreted by holocrine secretion, mixed in the lumen of the duct. Individuals of S. gigas had two types of lateral pedal glands, a large multicellular type and a tubular unicellular gland. The multicellular glands, which were surrounded by poorly developed muscle, contained one type of gland cell that stained for neutral and sulphated mucins only, as well as some support cells. The tubular glands contained a heterogeneous product that stained positively for neutral and sulphated mucins.

]]> 2009-07-02 info:doi/10.1093/mollus/eyp034 The Malacological Society of London 2009-07-02 ARTICLE http://mollus.oxfordjournals.org/cgi/content/short/eyp032v1?rss=1 Recent bottom trawl surveys in the North Sea have broadened our understanding of an obscure group of bobtail squids (Sepiolidae: Sepiolinae). There are at least two Sepietta species in this region, viz. Sepietta oweniana and Sepietta neglecta, and three Sepiola species, one of which is undescribed, viz. Sepiola atlantica, Sepiola pfefferi and Sepiola sp. nov. Sepiola pfefferi is distinct from Sepiola aurantiaca because of differences in the hectocotylus; the type localities of both species are far apart and data in GenBank indicate a substantial genetic difference between them. It is unclear how to distinguish Sepiola sp. nov. morphologically from its sister species S. atlantica, but molecular phylogenetic analyses and distributional data readily set them apart. The occurrence of Sepiola rondeleti in the northeastern Atlantic could not be confirmed. Several obviously incorrect or dubious identifications regarding GenBank data are listed.

]]> 2009-07-02 info:doi/10.1093/mollus/eyp032 The Malacological Society of London 2009-07-02 ARTICLE http://mollus.oxfordjournals.org/cgi/content/short/eyp028v1?rss=1 The reproductive biology of three Carpathian clausiliids of the genus Vestia [V. gulo (E.A. Bielz, 1859), V. elata (Rossmässler, 1836) and V. turgida (Rossmässler, 1836)] was studied using two methods: (1) the presence of eggs was examined in uteri of snails collected in the wild; and (2) the reproduction of snails was observed for 2–4 years under laboratory conditions. All three species retained eggs (ovoviviparity sensu lato), but there was a variation in the stage of the development of embryos among the species: V. gulo retained embryos to a size of c. 1.3 embryonic whorls, then laid eggs that hatched after 7–10 days; V. elata retained embryos to a size of 1.8 whorls, then laid eggs that hatched after 2–4 days; and V. turgida retained the largest embryos with up to 2.9 embryonic whorls. Oviposition was observed rarely in the latter species so that most embryos probably hatched inside the parent (ovoviviparity sensu stricto). The number of retained eggs in a uterus differed significantly between V. gulo and V. turgida. The reproductive period of V. turgida was longer than that of V. gulo, with two distinct reproductive peaks in June and August. Eggs were spherical or slightly oval, partly calcified and resilient, but eggs of V. turgida were elongated and less resilient. Mean numbers of eggs in a single batch were: V. gulo, 9.44 ± 3.73; V. elata, 4.50 ± 2.07; and V. turgida, 3.83 ± 2.12. Egg cannibalism was most intense in V. gulo, but was not observed in V. turgida. Under laboratory conditions V. gulo produced 1–4 batches, V. elata 1–7 batches and V. turgida 1–6 batches of eggs. The three species each produce up to 30–34 juveniles per reproductive season, but the interspecific variation and between-season variation were very high. A possible relation of the reproduction mode with habitat preferences of the species is proposed.

]]> 2009-06-17 info:doi/10.1093/mollus/eyp028 The Malacological Society of London 2009-06-17 ARTICLE http://mollus.oxfordjournals.org/cgi/content/short/eyp035v1?rss=1 The snail-trematode host-parasite system has been widely studied, as trematodes are known to greatly influence the fitness of their hosts. Indeed, during their development, the trematodes castrate the snail and one possible consequence of infection is gigantism of the snail. Snail gigantism is usually investigated experimentally by comparing the size of healthy and artificially infected snails. Here, I focused on naturally infected populations in order to investigate if snails submitted to trematode pressure have evolved specific life-history traits to respond to the parasite prevalence in their natural population. To this end, I estimated the correlations between measures of size (obtained from healthy laboratory individuals originating from populations) and the parasite prevalence at the population level. I found that the adult size of populations was positively correlated with population prevalence, an indication that gigantism might be operating. Moreover, I found a positive relation between growth and fecundity in healthy populations, while no such trade off was found in highly parasitized populations, suggesting that there may be a cost in fecundity to this gigantism.

]]> 2009-06-16 info:doi/10.1093/mollus/eyp035 The Malacological Society of London 2009-06-16 ARTICLE http://mollus.oxfordjournals.org/cgi/content/short/eyp029v1?rss=1 The ligamental apparatus of Thracia comprises external and internal resilient components, as well as a calcified ossicle termed the lithodesma. All these elements have hitherto been considered portions of a single unit and their allometry and functional morphology interpreted as such. However, analyses of the fine structure of the hinge of a growth series of Thracia phaseolina using conventional light, confocal and scanning electron microscopy revealed that, instead, external and internal components comprise distinct, independent layers of fibrous ligament, each formed at different ontogenetic stages. The internal ligament, with a lithodesma along its mid-sagittal sector, comprises the sole early juvenile ligament of the species and its main function is to force the shell valves open, not align them as had been previously suggested. The external (parivincular) ligament only appears at a shell length of c. 2.5 mm, but grows faster than the internal ligament to become the main component of the hinge of adults. Two- and three-parameter power functions (simple and full allometric equations) were fitted to measurements of the different ligament parts, and the performance and appropriateness of these models in describing the allometry of each of the studied traits are evaluated. Use of the full allometric model is recommended whenever the body size (or other standard) at which a trait of interest arises lies within or close to the limits of the sampled range.

]]> 2009-06-09 info:doi/10.1093/mollus/eyp029 The Malacological Society of London 2009-06-09 ARTICLE http://mollus.oxfordjournals.org/cgi/content/short/eyp033v1?rss=1 2009-06-06 info:doi/10.1093/mollus/eyp033 The Malacological Society of London 2009-06-06 RESEARCH NOTE http://mollus.oxfordjournals.org/cgi/content/short/eyp031v1?rss=1 2009-06-06 info:doi/10.1093/mollus/eyp031 The Malacological Society of London 2009-06-06 RESEARCH NOTE http://mollus.oxfordjournals.org/cgi/content/short/eyp025v1?rss=1 Several species of the genus Nacella show high phenotypic intraspecific variability and only a few morphological characters can be used to identify them, so that their taxonomic status is unclear. In this work molecular markers were used to determine if the most frequent forms of the genus observed along the coast of Patagonia and Tierra del Fuego in Argentina (Nacella magellanica, Nacella deaurata, Nacella delicatissima and Nacella mytilina) are true species, or if some are morphotypes of a single species. Maximum Parsimony and Bayesian phylogenetic analyses of the partial sequence of the mitochondrial cytochrome oxidase I and cytochrome b genes showed a polytomy comprising most of the individuals of the genus Nacella analysed. Using cytochrome b, among all species tested, only N. mytilina formed a well-supported clade. Interspecific genetic distances among the four Nacella species were very low and similar to the intraspecific ones. On the contrary, intersimple sequence repeats (ISSRs) fingerprint analyses confirmed the differentiation of N. magellanica, N. deaurata and N. mytilina. The specimens of N. delicatissima were intermixed with the individuals of N. magellanica and N. deaurata, suggesting that N. delicatissima is not a separate species but an infrequent morphotype of each of the other two species. ISSR–PCR was more useful in revealing genetic differences among closely related species than mitochondrial DNA sequences. These results could be explained by recent speciation processes in these limpets of the Southwestern Atlantic.

]]> 2009-05-08 info:doi/10.1093/mollus/eyp025 The Malacological Society of London 2009-05-08 ARTICLE http://mollus.oxfordjournals.org/cgi/content/short/eyp024v1?rss=1 The egg capsules, eggs and embryos of the muricid gastropod Trophon acanthodes are described for the first time. Egg capsules are sessile, bulliform, semi-circular, about 20 mm in diameter, with a plug in the centre of the dorsal side. Sutures divide the capsule into two slightly asymmetrical halves. Recently-laid egg capsules contained about 6,000 uncleaved eggs with a diameter of 213–236 µm. The number of early embryos was 7–9 with a size of 320 x 320 to 820–880 µm. Nine prehatching embryos of 3.94 mm maximum shell height were found inside an older egg capsule without intracapsular eggs. Therefore it is concluded that several thousand nurse eggs were present when laid. SEM illustrations of shell embryos and radulae are provided. Comparison of shell and radula of embryos with the protoconch and radula of adults of T. acanthodes confirms that the egg capsule belongs to this species. Coronium coronatum has an extremely similar protoconch and this, together with the similar egg capsule morphology that is different from that of Trophon geversianus, supports the reassignment of T. acanthodes to the genus Coronium.

]]> 2009-05-08 info:doi/10.1093/mollus/eyp024 The Malacological Society of London 2009-05-08 ARTICLE http://mollus.oxfordjournals.org/cgi/content/short/eyp021v1?rss=1 The fan mussel Pinna nobilis is a rapidly growing suspension-feeding bivalve endemic to the Mediterranean Sea and usually inhabits seagrass meadows. This endangered bivalve assimilates carbon and nitrogen isotopic ratios in tissues from its food sources. The ¹³C and ¹⁵N signatures were used to demonstrate isotopic variation among three tissues (digestive gland, gills and muscle) and (for digestive gland and gills) between summer and winter. Isotopic values were in the order: gills muscle > digestive gland. The mean values of the isotopic signal for ¹³C were –20.41 ± 0.12, –19.78 ± 0.07 and –19.30 ± 0.5 and for ¹⁵N were 2.84 ± 0.11, 4.05 ± 0.14 and 3.51 ± 0.15 for the tissues digestive gland, gills and muscle, respectively. Seasonal variations (summer–winter) were found in the isotopic signals (¹³C and ¹⁵N) for digestive gland and gills of fan mussel. As a result, this study suggests muscle as the appropriate tissue for future trophic studies and indicates that isotopic signals should be compared in the same season. These ¹³C and ¹⁵N values are among the first available for P. nobilis and contribute to the library of values for marine invertebrates.

]]> 2009-05-08 info:doi/10.1093/mollus/eyp021 The Malacological Society of London 2009-05-08 ARTICLE http://mollus.oxfordjournals.org/cgi/content/short/eyp018v1?rss=1 Predation is an important selective agent in the evolution of gastropod shell form. The adaptive value of shell elongation, however, has received relatively little attention in the context of predation. Arguments for its functional significance include the hypothesis that shell elongation facilitates soft tissue withdrawal inside the shell, thus elongation may improve fitness when predation by shell entry is intense. Here we ask whether species with more elongate shells also retract more deeply, a long-held assertion that until now lacked empirical support. To do this, we measured shell elongation (shell height divided by breadth) and soft-tissue withdrawal depth (angular retraction) in 14 species of temperate marine snail, covering a wide range of shell forms. Results show shell elongation to be a good predictor of angular retraction across genera and distantly related species. However, the elongation-retraction relationship was not apparent in comparisons among closely related species (specifically, species of Nucella and Littorina), nor were there such relationships among individuals within species (except, perhaps, within a few species having high shell-shape diversity). Competing arguments for the functional significance of shell elongation are discussed, as is the potential role of environment in affecting shell elongation and withdrawal depth independently.

]]> 2009-05-08 info:doi/10.1093/mollus/eyp018 The Malacological Society of London 2009-05-08 ARTICLE http://mollus.oxfordjournals.org/cgi/content/short/eyp017v1?rss=1 This study analyses the composition and species richness of aquatic molluscan communities within a large sector (over 100 km) of the valley of the Bug, a large lowland river in eastern Poland. An attempt was also made to determine the number of samples sufficient to compile a representative mollusc list within the whole study area and in groups of water bodies representing different degree of permanence, as well as to test the completeness of sampling of the malacofauna. Within the study area, 54 mollusc species were found – 36 snails and 18 bivalves. Up to 27 species were recorded from individual sites with a mean of 8 ± 5 species per site. Mean number of species was significantly higher in permanent water bodies than in the two other site groups. Dominance patterns in molluscan communities and frequencies of individual species showed distinct differences within three groups of habitats differing in permanence. Species composition was related to permanence, size, depth, hydrological connectivity and successional stage of water bodies, as well as to the type of bottom sediments and macrophyte abundance. The aquatic malacofauna found within the study area was rich, comprising almost 90% of potential composition based on regional species lists. Rarefaction curves for the total malacofauna confirmed the low probability of finding additional species, whereas temporary and permanent water bodies showed incomplete species lists. About 20 samples should be sufficient to collect representative data in the study area and more than 60 samples would be necessary to collect a nearly complete dataset.

]]> 2009-05-08 info:doi/10.1093/mollus/eyp017 The Malacological Society of London 2009-05-08 ARTICLE http://mollus.oxfordjournals.org/cgi/content/short/eyp023v1?rss=1 Cistopus taiwanicus n. sp. is a medium to large benthic octopus. The primary diagnostic character for the genus Cistopus is the possession of eight mucous pouches set in the oral surface of the webs between each of the arm bases. This study describes the morphological characters of C. taiwanicus from Taiwanese waters and the histology of the mucous pouches. Cistopus taiwanicus can be distinguished from Cistopus indicus by enlarged suckers in mature males and lower sucker counts on normal arms and hectocotylized arm. The inner walls of the mucous pouches are composed of columnar epithelial cells and mucus is secreted from the epithelial cells. Cistopus taiwanicus shows sexual dimorphism in the openings of the mucous pouches; males possess radial white stripes around the mucous pores and significantly larger pore diameters.

]]> 2009-05-06 info:doi/10.1093/mollus/eyp023 The Malacological Society of London 2009-05-06 ARTICLE http://mollus.oxfordjournals.org/cgi/content/short/eyp022v1?rss=1 The aim of the present study was to provide additional information regarding the seasonal influence on structural parameters of the lysosomal system, as well as on the variation of lipids and lipofuscins, in the digestive gland of mussels Mytilus galloprovincialis, and thus to define the most suitable time for performing sampling procedures in biomonitoring studies. The parallel examination of these biological parameters indicated that in early summer there was a very active lysosomal system together with extremely limited lipofuscin inclusions and moderate amount of lipids in the digestive gland of mussels. In early winter, the lysosomal system was restricted, and at the same time raised lipofuscin content and reduced amount of lipids occurred. In early spring, lysosomes became active again and concurrently high lipofuscin material was detected, whereas lipids showed an increase relative to winter. The results lead to the conclusion that summer represents the most appropriate period for sampling in biomonitoring studies dealing with digestive gland parameters, at least in mussels from Thermaikos Gulf and possibly from the Mediterranean Sea in general. In addition, the relationship between the N-acetyl-β-hexosaminidase reaction and the presence of lipids in digestive gland lysosomes of mussels is discussed.

]]> 2009-05-06 info:doi/10.1093/mollus/eyp022 The Malacological Society of London 2009-05-06 ARTICLE http://mollus.oxfordjournals.org/cgi/content/short/eyp020v1?rss=1 Mechanisms constraining phenotypic evolution, such as functional trade-offs, can cause phenotypic divergence in a common adaptation to use of the same habitat. This hypothesis was tested by field observations and laboratory experiments in Hirasea, a genus of endemic land snails of the Ogasawara Islands. Hirasea operculina was found on the large leaves of palm trees and possessed an extremely flat shell. In some localities, H. chichijimana and H. diplomphalus tended to rest on the leaves of broad-leaved trees and on palm leaves, respectively, and in these localities these species possess a flat shell relatively similar to each other, although the former has a smaller number of whorls and a higher spire than the latter. In other localities, both of these species were found inside deep soil and with no difference in habitat use. In these cases, both species have a higher shell, but their morphologies are very different: H. chichijimana possesses a conical shell with a high spire and a small aperture, but H. diplomphalus has a discoidal shell with a deeply sunken spire and a large aperture. Experiments measuring the time needed for the snail to escape from a light to hide under artificial substrates showed that flatter shells were more advantageous to movement on substrates with foliated structures such as leaf litter, while higher shells were more advantageous on substrates with a fine particle structure such as soil. In one case, a relatively higher shell has been attained by a decrease of whorl expansion rate and an increase of whorl translation rate along the coiling axis (resulting in a high-conical shell with a high spire), and in the other by an increase of whorl expansion rate and a decrease of whorl translation rate (resulting in a discoidal shell with a sunken spire). Both appear to be adaptive responses to the same burrowing lifestyle. These findings suggest that phenotypic traits can be diverse, even if they result from a common adaptation to a shared environment, if the adaptive changes have occurred from different starting points.

]]> 2009-05-06 info:doi/10.1093/mollus/eyp020 The Malacological Society of London 2009-05-06 ARTICLE http://mollus.oxfordjournals.org/cgi/content/short/eyp019v1?rss=1 A broad zone of sympatry between two morphologically and ecologically similar blue mussels Mytilus trossulus (Gould) and M. edulis (L.) extends from the Canadian Maritimes into the Gulf of Maine. The zone boundary and the southern range limit of M. trossulus coincide with the position of the Eastern Maine Coastal Current (EMCC). This current has not been recognized as a biogeographic boundary. However, the flow field associated with the EMCC essentially divides the eastern and western Gulf during the part of year when mussel populations in the eastern portion of the Gulf are reproductively active and thus may be a hydrodynamic barrier to the westward dispersal of M. trossulus larvae. Alternatively, a strong gradient in water temperature associated with the EMCC may create a physiological barrier to M. trossulus larvae. We examined spatial variation in the abundance of M. trossulus and M. edulis along the coast of Maine using two diagnostic DNA-based markers. Although we detected M. trossulus in mussel populations in offshore locations in central Maine that were directly in the path of the EMCC, the abundance of this species declines dramatically at sites beyond the influence of this current. Variation in the abundance of adults, however, cannot differentiate between the effects of the EMCC on larval transport vs physiological tolerance. Thus, we also conducted a temperature challenge experiment investigating the species-specific variation in larval survival at temperatures ranging from 5°C to 20°C. We found that larval mortality was generally higher for M. trossulus relative to M. edulis larvae when exposed to 20°C early during development. These results suggest that differences in larval thermal tolerance help to structure the southern range limit for M. trossulus in the Gulf of Maine.

]]> 2009-05-06 info:doi/10.1093/mollus/eyp019 The Malacological Society of London 2009-05-06 ARTICLE http://mollus.oxfordjournals.org/cgi/content/short/eyp016v1?rss=1 A common question in studies of hybrid zones regards how nearby parental populations can remain distinct in the face of gene flow from the other species and hybrid populations. Environmentally dependent hybrid-zone models often invoke selection favouring each of the parental species in different habitats where immigrants will often fail to survive and reproduce. The present study tests whether a relatively pure population of Mytilus galloprovincialis, located on the edge of a hybrid zone with M. edulis, is being maintained by selection against hybrid immigrants. Comparisons of newly settled spat with members of the same cohort approximately 9 months later consistently show a reduction in M. edulis-specific alleles to levels observed in adult age classes at two diagnostic loci. These data provide evidence for selection against spat from the hybrid zone that settled at sites within the M. galloprovincialis population within the first year of life. The observed selection would result in removal of most M. edulis-specific alleles prior to reproduction and keep the M. galloprovincialis population distinct.

]]> 2009-04-28 info:doi/10.1093/mollus/eyp016 The Malacological Society of London 2009-04-28 ARTICLE http://mollus.oxfordjournals.org/cgi/content/short/eyp015v1?rss=1 2009-04-01 info:doi/10.1093/mollus/eyp015 The Malacological Society of London 2009-04-01 RESEARCH NOTE