Journal of Molluscan Studies - current issue

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