Muscular alteration of gill geometry in vitro: implications for bivalve pumping processes

In bivalves, water-pumping potential is determined both by ciliary activity and by the geometry of the system of passageways that acts as a conduit for water flow. Smooth muscles intrinsic to the gills of eulamellibranch bivalves possess the anatomical organization needed to regulate the dimensions of these water passageways. The tone of these muscles can be controlled experimentally using excitatory neurotransmitters to elicit muscle contraction and by removing Ca++ from the Ringer's solution to induce muscular relaxation. These experimental methods were used to investigate the effects of smooth muscle tone on the gill dimensions of two freshwater bivalves, Dreissena polymorpha and Corbicula fluminea, and one marine bivalve, Mercenaria mercenaria. In addition, endoscopic observations were made from the suprabranchial chamber of a freshwater unionid, Lampsilis anodontoides. Contraction of gill muscles led to a significant reduction in interfilament width, internal ostial area, and the cross-sectional area of the water tubes. Endoscopic observation from minimally disturbed L. anodontoides revealed rapid constriction of the water tubes upon contraction of the muscles of the gill and gill axis. Taken together, these data support the idea that alteration of smooth muscle tone in the gill provides a mechanism for controlling water-pumping activities.

Hydrobia ulvae (Gastropoda: Prosobranchia): a new model for regeneration studies

Within 2 weeks of decapitation, Hydrobia ulvae was able to regenerate new head structures including buccal ganglia. It was also capable of regenerating propodial ganglia after anterior foot amputation. The functional regeneration of the buccal ganglia was demonstrated by behavioural observations and by electrophysiological experiments. The presence of the oesophagus was shown to be important for regeneration of the buccal complex. H. ulvae provides a new model for regeneration studies, so details of the topographic anatomy and biology of this species are described. To standardize experimental animals in future studies, the effects of age, sex and trematode infestation on the regeneration capacity of H. ulvae have been evaluated. The high capacity for regeneration together with the possibility of using electrophysiological techniques makes H. ulvae a favourable model in which to study neurogenesis in adult animals.

Invariant size-frequency distributions along a latitudinal gradient in marine bivalves

In the most extensive analysis of body size in marine invertebrates to date, we show that the size-frequency distributions of northeastern Pacific bivalves at the provincial level are surprisingly invariant in modal and median size as well as size range, despite a 4-fold change in species richness from the tropics to the Arctic. The modal sizes and shapes of these size-frequency distributions are consistent with the predictions of an energetic model previously applied to terrestrial mammals and birds. However, analyses of the Miocene-Recent history of body sizes within 82 molluscan genera show little support for the expectation that the modal size is an evolutionary attractor over geological time.

[Morphofunctional characteristics of the mollusk foot in relation with ecology]

The level of mollusk foot development and swelling primarily depends on the mode of life and functional load of the tissues. It is highest for the polyfunctional foot, which is mediated by its specific structural features.

Molluscan engrailed expression, serial organization, and shell evolution

Whether the serial features found in some molluscs are ancestral or derived is considered controversial. Here, in situ hybridization and antibody studies show iterated engrailed-gene expression in transverse rows of ectodermal cells bounding plate field development and spicule formation in the chiton, Lepidochitona cavema, as well as in cells surrounding the valves and in the early development of the shell hinge in the clam, Transennella tantilla. Ectodermal expression of engrailed is associated with skeletogenesis across a range of bilaterian phyla, suggesting a single evolutionary origin of invertebrate skeletons. The shared ancestry of bilaterian-invertebrate skeletons may help explain the sudden appearance of shelly fossils in the Cambrian. Our interpretation departs from the consideration of canonical metameres or segments as units of evolutionary analysis. In this interpretation, the shared ancestry of engrailed-gene function in the terminal/posterior addition of serially repeated elements during development explains the iterative expression of engrailed genes in a range of metazoan body plans.

Fast and flexible: the cephalopod repertoire

The cephalopods differ remarkably from their molluscan cousins such as snails and bivalves. Fast moving, active predators, they have behavioural and physiological capabilities that stimulate and fascinate marine zoologists. Research on their methods of prey capture and handling, in particular, demonstrates the adaptability of the cephalopod format.

Evidence for a distinct light-induced calcium-dependent potassium current in Hermissenda crassicornis

A model of phototransduction is developed as a first step toward a model for investigating the critical interaction of light and turbulence stimuli within the type B photoreceptor of Hermissenda crassicronis. The model includes equations describing phototransduction, release of calcium from intracellular stores, and other calcium regulatory mechanisms, as well as equations describing ligand-gating of a rhabdomeric sodium current. The model is used to determine the sources of calcium in the soma, whether calcium or IP3 is a plausible ligand of the light-induced sodium current, and whether the light-induced potassium current is equivalent to the calcium-dependent potassium current activated by light-induced calcium release. Simulations show that the early light-induced calcium elevation is due to influx through voltage-dependent channels, whereas the later calcium elevation is due to release from intracellular stores. Simulations suggest that the ligand of the fast, light-induced sodium current is IP3 but that there is a smaller, prolonged component of the light-induced sodium current that is activated by calcium. In the model, the calcium-dependent potassium current, located in the soma, is activated only slightly by light-induced calcium elevation, leading to the prediction that a calcium-dependent potassium current, active at resting potential, is located in the rhabdomere and is responsible for the light-induced potassium current.

The use of imposex to assess tributyltin contamination in coastal waters and open seas

Imposex in muricid gastropods has been used to monitor tributyltin (TBT) contamination worldwide. Pollution was severe during the 1980s but regulations prohibiting the use of TBT-based antifoulants on vessels < 25 m in length have been highly effective in reducing TBT levels in coastal waters. Large vessels are still sources of TBT and major ports, especially those with dry docking and repair facilities, continue to be hot-spots of contamination. Measures of imposex suggest that severe pollution is normally localised to within a few kilometres of them. Mild imposex, possibly as a result of TBT pollution (although other causes have not been ruled out), has been described in whelks Buccinum undatum from offshore waters of the southern and central North Sea. However, the species is still abundant there and the occurrence of imposex does not seem to have affected its breeding performance. Imposex was mild or absent in populations of dogwhelks from open oceanic sites around the north Atlantic Ocean, suggesting that the oceans are free of contamination at biologically significant levels.

ILME: a waterborne pheromonal peptide released by the eggs of Sepia officinalis

A novel tetrapeptide modulating the oviduct contractions was characterized from egg mass of Sepia officinalis. After two purification steps by rpHPLC, an apparent pure fraction containing the biological activity was submitted to MALDI-TOF analysis. The mass spectrum revealed 6 peaks of m/z 293, 505, 596, 613, 728, and 745. The tissue peptide mapping performed in LC-MS demonstrated the occurrence of the m/z 505 peptide in the follicles, the full-grown oocytes, and in the eggs. This peptide was also recovered in the seawater after the incubation of full grown oocytes or eggs, demonstrating a release in the genital tract and in the environment. Edman degradation gave the following sequence: Ileu-Leu-Met-Glu. The synthetic peptide applied to the whole genital tract triggered a cyclisation of the contractions at 10(-14) M. ILME appeared to be a chemical messenger released by the oocytes and the eggs, and was able to exert both paracrine and pheromonal activity.

Structure and composition of the aragonitic crossed lamellar layers in six species of Bivalvia and Gastropoda

The microstructures, the chemical composition and the soluble organic matrices of the aragonitic crossed lamellar layers of the shells of six species of molluscs have been studied. The microstructures and chemical contents are similar, whereas the quantities of organic matrices are variable. All the soluble matrices are glycoproteins, with low S contents. Their molecular weights, the protein-sugar ratios and acidities are variable. Neither a gastropod nor a bivalve pattern is recognized. The diversity of the organic matrices probably plays a main role in the fossilization processes of mollusc shells.

Neuronal components of the superior and inferior tentacles in the terrestrial slug, Limax marginatus

To identify the types of neurons and to infer the patterns of connectivity in slug tentacles, we stained the neurons in the superior and inferior tentacles in the terrestrial slug, Limax marginatus, by backfilling of the tentacular nerves with Lucifer yellow. Four types of stained neurons, '(1) sensory neurons', '(2) gamma cells', '(3) ganglion cells', '(4) lateral cells', were identified both in the superior and inferior tentacles. Three subtypes of the sensory neurons, '(1a) round sensory neurons', '(1b) spindle-shaped sensory neurons', and '(1c) small sensory neurons', were found in the digits. The gamma cells and the ganglion cells were interneurons. Three subtypes of gamma cells, '(2a) round monopolar gamma cells', '(2b) round bipolar gamma cells', and '(2c) large gamma cells', were present in the digits. The ganglion cells were composed of '(3a) monopolar ganglion cells', '(3b) bipolar ganglion cells', and '(3c) elongated ganglion cells'. The monopolar and bipolar types were located both in the tentacular ganglia and digits, whereas the elongated type was present only in the tentacular ganglia. The lateral cells, whose function is unknown, were found in the dermo-muscular sheaths of the tentacles. Our study provides the first description of the neuronal map of inferior tentacles in gastropods. The results showed no differences in the morphological features of stained neurons between the superior and inferior tentacles in L. marginatus.

Insights into early molluscan neuronal development through studies of transmitter phenotypes in embryonic pond snails

Pond snails have long been the subject of intense scrutiny by researchers interested in general principles of development and also cellular and molecular neurobiology. Recent work has exploited both these fields of study by examining the ontogeny of the nervous system in these animals. Much of this work has focussed upon the development of specific transmitter phenotypes to provide vignettes of neuronal subpopulations that can be traced from early embryonic life through to adulthood. While such studies have generally confirmed previous explanations of gangliogenesis in gastropods, they have also indicated the presence of several neurons that appear earlier and in positions inconsistent with classical views of gastropods neurogenesis. The earliest of these cells contain FMRFamide-related peptides and have anteriorly projections that mark the future locations of ganglia and interconnecting pathways that will comprise the postembryonic central nervous system. These posterior, peptidergic cells, as well as certain, apical, monoaminergic neurons, disappear and apparently die near the end of embryonic life. Finally, populations of what appear to be peripheral sensory neurons begin to express catecholamines by around midway through embryonic life. Like several of the neurons expressing a variety of transmitters in the developing central ganglia, the catecholaminergic peripheral cells persist into postembryonic life. Transmitter phenotypes, cell shapes and locations, and neuritic morphologies all suggest that many of the neurons observed in early embryonic pond snails have recognizable homologues across the molluscs. Such observations have profoundly altered our views of neurogenesis in gastropods over the last few years. They also suggest the promise for pond snails as fruitful models for studying the roles and mechanisms for pioneering fibres, cues triggering apoptosis, and contrasting origins and mechanisms employed for generating central vs. peripheral neurons within a single organism.

A new species of Trapania (Nudibranchia: Goniodorididae) from the Pacific coast of Central America

A new marine gastropod species of the genus Trapania Pruvot-Fol, 1931, is described from Cabo Blanco, Puntarenas, Costa Rica and from Islas Secas, Panamá. Trapania inbiotica sp. nov. has a white body with red patches, white rhinophores with some little red patches, yellow appendages with partially red bases. The radula is composed of 28 rows of teeth. Each tooth has a large conical cusp with 21-24 denticles. Two or three of those denticles on the inner side of the cusp are smaller than the others. There are also 1-3 small denticles on the outside of the cusp. The jaw elements are very irregular.

Cuttlebone morphology limits habitat depth in eleven species of Sepia (Cephalopoda: Sepiidae)

The cuttlebone is a rigid buoyancy tank that imposes a depth limit on Sepia, the only living speciose cephalopod genus with a chambered shell. Sections of 59 cuttlebones from a geographically diverse sample of 11 species were examined using confocal microscopy. Sepia species that live at greater depths had thicker septa and less space between pillars than did shallow species. A plate theory analysis of cuttlebone strength based on these two measures predicted maximum capture depths accurately in most species. Thus cuttlebone morphology confers differing degrees of strength against implosion from hydrostatic pressure, which increases with increasing habitat depth. Greater strength may come at the cost of increased cuttlebone density, which impinges on the cuttlebone's buoyancy function.

Evolutionary exploitation of design options by the first animals with hard skeletons

The set of viable design elements available for animals to use in building skeletons has been fully exploited. Analysis of animal skeletons in relation to the multivariate, theoretical "Skeleton Space" has shown that a large proportion of these options are used in each phylum. Here, we show that structural elements deployed in the skeletons of Burgess Shale animals (Middle Cambrian) incorporate 146 of 182 character pairs defined in this morphospace. Within 15 million years of the appearance of crown groups of phyla with substantial hard parts, at least 80 percent of skeletal design elements recognized among living and extinct marine metazoans were exploited.

Mosaic arrangement of SCP(B-), FMRFamide-, and histamine-like immunoreactive sensory hair cells in the statocyst of the gastropod mollusc Pleurobranchaea japonica

A pair of statocysts are located in the periganglionic connective tissue of the pedal ganglia of the opisthobranch mollusc Pleurobranchaea japonica. Light- and electron-microscopic observations show that the sensory epithelium of the statocyst consists of 13 disk-shaped hair cells. Each hair cell sends a single axon to the cerebral ganglion through the static nerve. Neurotransmitters in the hair cells were examined by means of immunocytochemistry. Our results show that the 13 sensory hair cells include two SCPB-, three FMRFamide-, and eight histamine-like immunoreactive cells. One hair cell contains a transmitter substance other than SCPB-, FMRFamide, histamine, serotonin, or GABA. One of the two SCPB-like immunoreactive cells, located in the ventral region of the statocyst, is the largest cell in the statocyst. The other, located in the anterodorsal region, shows co-immunoreactivity to both SCPB and FMRFamide antisera. Among the three FMRFamide-like immunoreactive hair cells, one is located in the posteroventral region, separated from the other two, which are adjacent to each other in the anterodorsal region. All the eight histamine-like immunoreactive hair cells are adjacent to one another, occupying the remainder of a triangular pyramid-shaped region. These immunoreactive cells are symmetrically placed in the right and left statocysts. This mosaic arrangement was identical among specimens. Thus the static nerve may code information about position or movement of the statoliths, with the use of different transmitters in the mosaic arrangement of the hair cells.

Size dependent bioaccumulation of heavy metals by Mytilopsis sallei (Recluz) at Visakhapatnam harbour

Relationship between body size and bioaccumulation of copper, zinc, lead and cadmium in the fouling bivalve, M. sallei (Recluz) in Visakhapatnam harbour was studied. While concentration of copper, zinc and lead decrease with increasing size, no such relationship is observed for cadmium.

Comparative study of the apical ganglion in planktotrophic caenogastropod larvae: ultrastructure and immunoreactivity to serotonin

Previous research suggests that a major role of the apical ganglion (also called the apical or cephalic sensory organ) in gastropod larvae is detection and integration of sensory information and relay of motor signals to effectors in the velum. However, the relative impact of ancestry versus velum size and life history on characteristics of the apical ganglion is unresolved. We address this issue by contributing data on the apical ganglion and overlying epidermis in planktotrophic larvae of four caenogastropod species (Euspira [Polinices] lewisii, Lacuna vincta, Trichotropis cancellata, and Amphissa versicolor) derived from light microscopy, scanning and transmission electron microscopy, and immunohistochemical localization of serotonin-like antigenicity. Ultrastructure of the apical ganglion is similar in these caenogastropods, and the basic plan corresponds to previous descriptions of the apical ganglion in planktotrophic opisthobranch larvae (subgroup of Heterobranchia). The only identified structural feature that is unique to all these caenogastropods, relative to opisthobranchs, is modified ciliary axonemes for the ampullary cells, a distinctive type of sensory neuron. Like opisthobranch larvae, caenogastropod larvae have serotonin-immunoreactive neurons within the apical ganglion; the number ranges from three to six, but a lateral pair of serotonergic, nonsensory neurons is common to all species. The pattern of serotonergic neurons in E. lewisii, which develops large, subdivided velar lobes, is the same as that of opisthobranch larvae, which have a relatively small, unelaborated velum. These and other data suggest that common ancestry is a major determinant of overall structural design for the apical ganglion in caenogastropods and heterobranchs, which are sister groups within the Gastropoda. Velum size and life history strategy may account for some, but not all, cases of interspecific differences in the serotonergic component.

Histopathology of the digestive gland of an Antarctic limpet exposed to cadmium

Histopathological alterations induced experimentally with cadmium (Cd) in Antarctic limpets (Nacella concinna), exposed for different times and concentrations were compared to controls. At the light microscope level, samples exposed to the contaminant for short periods (6, 12 and 24 h) at two different concentrations (0.25 and 0.5 mg l(-1)) showed no alterations compared to controls. After 48 h of exposure at a 0.5 mg l(-1) Cd concentration, vacuolisation of the basophilic cells was observed. After 72 h exposure, there was a marked loss of all the digestive gland structure, with cell autolysis and loss of basophilia.

Energy storage by passive elastic structures in the mantle of sepia officinalis

The passive elastic properties of the mantle of the cuttlefish Sepia officinalis have been characterized in experiments on intact mantle and on pieces cut from the mantle. The mantle was found to be very compliant over a wide range of circumferential strains, corresponding to a change in mantle circumferential strain of 0.45. Beyond this range of strain, the mantle was much stiffer, in both the circumferential direction, 0.542+/−0.025 MPa (mean +/− s.e.m., N=51) and through the thickness of the mantle wall, 0.152+/−0.041 MPa (N=11). Almost 80 % of the work done on the tissue during compression in the circumferential direction was recovered during elastic recoil of the tissue; this elastic work could contribute to refilling the mantle after a jet. Our estimates of the work done during a cycle of jetting and refilling show that such elastic work is small (approximately 1 %) compared with the contractile work done by the circular muscle fibres. However, although the elastic work is almost negligible in the overall energy budget, it is probably sufficient to power refilling of the mantle.

Discrimination and phylogeny of solenogaster species through the morphology of hard parts (Mollusca, Aplacophora, Neomeniomorpha)

Ten species in five genera and three families from continental shelf and deep-sea collections of neomenioid Aplacophora (Mollusca) are described, emphasizing external anatomy and hard parts--body shape, radula, epidermal spicules, and copulatory spicules--as well as the reproductive system. One genus and seven species are new: Plawenia n.g., Plawenia sphaera, P. argentinensis, Dorymenia tortilis, Eleutheromenia bassensis, E. mimus, Kruppomenia levis, and K. delta. Also included are redescriptions of three published species, emphasizing hard parts for comparisons with the new species and genus: Dorymenia sarsii (Koren & Danielssen), Simrothiella margaritacea (Koren & Danielssen), and Plawenia schizoradulata (Salvini-Plawen). A cladistic analysis of species described here demonstrates the usefulness of hard parts for phylogeny. Specimens came from collections made in the southwest Pacific and the southwest and northeast Atlantic.

Accommodation in the cuttlefish (Sepia officinalis)

We have studied natural accommodation in the eye of six specimens of cuttlefish (Sepia officinalis) as they were fed with fish and shrimp. Using infrared photoretinoscopy, we observed (1) that the resting refractive state of the cuttlefish was emmetropic or slightly hyperopic, (2) that accommodation took place only a fraction of a second before a strike and (3) that accommodation focused selectively only in the frontal visual field while no change in refraction could be measured in the lateral field of view. Accommodation was bilateral and amounted to approximately 5 diopters (the reciprocal of the focal length expressed in meters). Simultaneously, the eyes converged. It appears that, as in most teleost fishes, accommodation in the cuttlefish involves a movement of the crystalline lens perpendicular to the axis of the eye. In histological sections, we observed the position and arrangement of the ciliary muscles, confirming earlier anatomical descriptions, and developed a model of how accommodation could be achieved.

Molecular phylogenetics and the evolution of labral spines among eastern Pacific ocenebrine gastropods

Labral spines are sharp projections of the apertural lip found in some marine gastropods that are used to penetrate hard-shelled prey. The majority of gastropod genera that contain labral spine-bearing species are found in the subfamily Ocenebrinae (Gastropoda: Muricidae). To reconstruct the evolutionary history of labral spine-bearing and labral spine-lacking gastropods in the eastern Pacific (EP) Ocean, partial sequences of two mitochondrial genes (cytochrome oxidase I and 12S rRNA) were obtained from representative taxa. Despite high nucleotide bias, a variety of phylogenetic reconstruction methods produced the same tree topology. The traditional taxonomic view that all "Nucella-like" spine-bearing taxa in the EP belong to a monophyletic "Acanthina" is rejected due to nonmonophyly of this group. The more recently recognized "Acanthinucella" is also not monophyletic, and we therefore propose the new genus Mexacanthina for two Mexican species formerly assigned to Acanthinucella. The genus Ocinebrina, which first appears in the middle Eocene, is not a stem EP ocenebrine lineage and may also not be a monophyletic clade. Tracing the evolutionary history of labral spines among extant lineages indicates that the absence of a labral spine is ancestral for all EP ocenebrines. Ancestral conditions could not be resolved unambiguously for all nodes of the phylogeny based on extant taxa. However, by jointly considering both molecular phylogenetic relationships and the phylogenetic affinities of several extinct taxa, all remaining character state transformation can be inferred unambiguously. Based on this analysis, a labral spine likely evolved independently in at least four lineages of EP ocenebrines. Although homoplasy appears to characterize labral spine evolution among ocenebrine gastropods, the structural position of a labral spine was evolutionarily altered in one lineage, indicating that different types of labral spines do not necessarily reflect convergent evolution.

Historical and biomechanical analysis of integration and dissociation in molluscan feeding, with special emphasis on the true limpets (Patellogastropoda: Gastropoda)

Modifications of the molluscan feeding apparatus have long been recognized as a crucial feature in molluscan diversification, related to the important process of gathering energy from the environment. An ecologically and evolutionarily significant dichotomy in molluscan feeding kinematics is whether radular teeth flex laterally (flexoglossate) or do not (stereoglossate). In this study, we use a combination of phylogenetic inference and biomechanical modeling to understand the transformational and causal basis for flexure or lack thereof. We also determine whether structural subsystems making up the feeding system are structurally, functionally, and evolutionarily integrated or dissociated. Regarding evolutionary dissociation, statistical analysis of state changes revealed by the phylogenetic analysis shows that radular and cartilage subsystems evolved independently. Regarding kinematics, the phylogenetic analysis shows that flexure arose at the base of the Mollusca and lack of flexure is a derived condition in one gastropod clade, the Patellogastropoda. Significantly, radular morphology shows no change at the node where kinematics become stereoglossate. However, acquisition of stereoglossy in the Patellogastropoda is correlated with the structural dissociation of the subradular membrane and underlying cartilages. Correlation is not causality, so we present a biomechanical model explaining the structural conditions necessary for the plesiomorphic kinematic state (flexoglossy). Our model suggests that plesiomorphically the radular teeth must flex laterally as they pass over the bending plane as a result of the mechanical restrictions in the flexible but inelastic subradular membrane and close association between subradular membrane and cartilages. Relating this model to the specific character states of the clades, we conclude that lack of flexure in patellogastropods is caused by the dissociation of the subradular membrane and cartilage supports.

Effect of heavy metals (Cu, Cd and Pb) on aspartate and alanine aminotransferase in Ruditapes philippinarum (Mollusca: Bivalvia)

The accumulation of cadmium, copper and lead and their effects on aspartate and alanine aminotransferases in digestive gland, gills, foot and soft body in the clam Ruditapes philippinarum were examined. The animals were exposed to different concentrations: Cd (200-600 micrograms.l-1), Pb (350-700 micrograms.l-1) and Cu (10-20 micrograms.l-1) for 7 days. The highest concentrations were found in digestive gland for cadmium and copper, and in gills for lead, and the lowest values were observed in the foot. Aspartate aminotransferase activity (AST), in general, was not inhibited by cadmium, lead or copper during the exposure. Only in clams exposed to cadmium (600 micrograms.l-1, 7 days) and copper (20 micrograms.l-1, 5 days) were observed significant differences (P < 0.05) in foot and gills, respectively, with respect to control. In the case of alanine aminotransferase activity (ALT), significant differences were observed for cadmium and lead in treated animals with respect to control. With regard to copper, a decrease in ALT was observed in gills and foot exposed to 20 micrograms.l-1. A significant correlation (P < 0.05) was observed between ALT and metal accumulation for cadmium, copper and lead in gills. In the case of soft body, only cadmium and lead showed a significant correlation. In summary, R. philippinarum can be considered a bioindicator species for cadmium and lead accumulation and ALT could be useful as biomarker of sublethal stress for these metals in soft tissues and gills can be considered an adequate target tissue for copper.

Cellular and subcellular structure of anterior sensory pathways in Phestilla sibogae (Gastropoda, Nudibranchia)

Two sensory-cell types, subepithelial sensory cells (SSCs) and intraepithelial sensory cells (ISCs), were identified in the anterior sensory organs (ASO: pairs of rhinophores and oral tentacles, and the anterior field formed by the oral plate and cephalic shield) of the nudibranch Phestilla sibogae after filling through anterior nerves with the neuronal tracers biocytin and Lucifer Yellow. A third type of sensory cells, with subepithelial somata and tufts of stiff-cilia (TSCs, presumably rheoreceptors), was identified after uptake of the mitochondrial dye DASPEI. Each sensory-cell type has a specific spatial distribution in the ASO. The highest density of ISCs is in the oral tentacles (approximately 1,200/mm2), SSCs in the middle parts of the rhinophores (>4,000/mm2), and TSCs in the tips of cephalic tentacles (100/mm2). These morphologic data, together with electrophysiologic evidence for greater chemical sensitivity of the rhinophores than the oral tentacles (Murphy and Hadfield [1997] Comp. Biochem. Physiol. 118A:727-735; Boudko et al. [1997] Soc. Neurosci. Abstr. 23:1787), led us to conclude that the two pairs of chemosensory tentacles serve different chemosensory functions in P. sibogae; i.e., ISCs and the oral tentacles serve contact- or short-distance chemoreception, and SSCs and the rhinophores function for long-distance chemoreception or olfaction. If this is true, then the ISC subsystem probably represents an earlier stage in the evolution and adaptations of gastropod chemosensory biology, whereas among the opisthobranchs, the SSC subsystem evolved with the rhinophores from ancestral cephalaspidean opisthobranchs.

[Conus venoms: a source of toxins which interact with membrane- potential-dependent sodium channels]

Marine snails of the genus Conus, as they are carnivorous predators, have a venom apparatus used to capture their prey. The toxins contained in the venoms of Conidae, called conotoxins, are of a particular high degree of diversity and represent powerful tools in the neuroscience field. Indeed, these toxins specifically bind with a high affinity to receptors and ionic channels. Therefore, they provide original pharmacological tools which receive increasing investigation both to identify and study some functions of the nervous systems and to characterize new types and closely related subtypes of receptors or ionic channels. The voltage-gated sodium channel, because of its fundamental role in cell membrane excitability, is the specific target of a large number of animal and vegetal toxins. Actually, at least seven toxin receptor sites have been identified on this channel-protein. These toxins, and in particular conotoxins, are used to precise the role of different types and/or closely related subtypes of sodium channels in the peripheral and central nervous systems. The focus of the present review is to summarize our current knowledge of the consequences of physiological interactions between different conotoxin families and sodium channels.

Studies on shell formation. IX. An electron microscope study of crystal layer formation in the oyster

Details of crystal growth in the calcitostracum of Crassostrea virginica have been studied with the purpose of analyzing the formation of the overlapping rows of oriented tabular crystals characteristic of this part of the shell. Crystal elongation, orientation, and dendritic growth suggest the presence of strong concentration gradients in a thin layer of solution in which crystallization occurs. Formation of the overlapping rows can be explained by three processes observed in the shell: a two-dimensional tree-like dendritic growth in which one set of crystal branchings creeps over an adjacent set of branchings; three-dimensional dendritic growth; and growth by dislocation of crystal surfaces. Multilayers of crystals may thus be formed at one time. This is favored by infrequent secretion of a covering organic matrix which would inhibit crystal growth. The transitional zone covering the outer part of the calcitostracum and the inner part of the prismatic region is generally characterized by aggregates of small crystals with definite orientation. Growth in this zone appears to take place in a relatively homogeneous state of solution without strong concentration gradients. Thin membranes and bands of organic matrix were commonly observed in the transitional zone bordering the prismatic region. The membrane showed a very fine oriented network pattern.

Structure of the conchiolin cases of the prisms in Mytilus edulis Linne

The prisms in the shell of Mytilus edulis Linné are calcite needles. Their small size and their thin conchiolin cases distinguish them from the prisms of many other species of mollusks. These Mytilus prisms have been studied with the electron microscope. The material consisted of positive replicas of surfaces of the prismatic layer, etched with chelating agents, and of preparations of tubular cases from decalcified prisms which were compared with the conchiolin from decalcified mother-of-pearl of the same species. In the replicas, the cases appear as thin pellicles in the intervals between the prism crystals. Both the prism cases and the nacreous conchiolin, disintegrated by exposure to ultrasonic waves and sedimented on supporting films, appear in the form of tightly meshed, reticulated sheets, described as "tight pelecypod pattern" in former studies on nacreous conchiolin of Mytilus. The results show that in the shell of this species the same conchiolin structure is associated with aragonite in mother-of-pearl and with calcite in the prismatic layer.

The relationship between the fine structure and direction of beat in gill cilia of a lamellibranch mollusc

This paper describes the fine structure and its relationship to the direction of beat in four types of cilia on the gill of the fresh-water mussel Anodonta cataracta. The cilia contain nine outer, nine secondary, and two central fibers, such as have been described previously in other material. Each outer fiber is a doublet with one subfiber bearing arms. One particular pair of outer fibers (numbers 5 and 6) are joined together by a bridge. The two central fibers are enclosed by a central sheath; also present in this region is a single, small mid-fiber. The different groups of fibers are connected together by radial links that extend from the outer to the secondary fibers, and from the secondary fibers to the central sheath. The basal body consists of a cylinder of nine triplet fibers. Projecting from it on one side is a dense conical structure called the basal foot. The cylinder of outer fibers continues from the basal body into the cilium, passing through a complex transitional region in which five distinct changes of structure occur at different levels. There are two sets of fibers associated with the basal bodies: a pair of striated rootlets that extends from each basal body down into the cell, and a system of fine tubular fibers that runs parallel to the cell surface. The relationship between fine structure and direction of beat is the same in all four types of cilia examined. The plane of beat is perpendicular to the plane of the central fibers, with the effective stroke toward the bridge between outer fibers 5 and 6, and toward the foot on the basal body.

Zonal rotor purification and characterization of "mannosomes": a tubular membrane system in gastropod mollusc digestive gland

Mannitol oxidase (manox) is an H2O2-generating oxidase apparently unique to molluscs and especially abundant in alimentary tissues. In the digestive gland it is localized to an organelle ("mannosome") that forms an unusual tubular membrane system. We have developed a novel centrifugation procedure for >100-fold purification of these membranes in 20% yield from approximately 30 g of digestive gland of the slug Arion ater. Mannosomes from several other gastropod species are also substantially purified by the procedure. Four successive density gradient separations are employed which minimize structural damage by exploiting near isosmotic conditions early on and by completely avoiding traumatic pelleting and resuspension. Plasma membrane contamination is reduced by digitonin-induced density perturbation. The purified preparation is characterized by a predominant 68-kDa integral membrane protein and retains the in situ appearance of hexagonally arranged tubules with an enveloping outer membrane.

Field studies on imposex and organotin accumulation in the rock shell, Thais clavigera, from the Seto Inland Sea and the Sanriku region, Japan

Field studies on imposex and organotin (butyltin and phenyltin) contamination in the Japanese molluscs (the rock shell, Thais clavigera, and the Pacific oyster, Crassostrea gigas) were conducted along the coast of both the Seto Inland Sea and the Sanriku region, Japan, during February-March 1996. The percentage occurrence of imposex in the rock shell, Thais clavigera, was still 100% at all sites surveyed (22 and seven sites in the Seto Inland Sea and the Sanriku regions, respectively). Observed values of the Relative Penis Length (RPL) index (%), defined as the ratio of mean penis length in females to that in males, exceeded 50 at many sites. Sterile individuals whose oviducts were blocked by vas deferens formation were also extensively observed. Tissue concentrations of organotin compounds in the rock shell and the Pacific oyster were higher than those from other areas of Japan. The degree of imposex (RPL index) was correlated with the sum of TBT and TPT concentrations in tissue of the rock shell. Less recovery from imposex in the rock shell and less amelioration of TBT pollution were observed, suggesting that organotin use in antifouling paints has still continued for vessels larger than 25 m in length and that it has influenced imposex symptoms in the rock shell.

Kinetics of the structure of neurites in mollusk brain after its dissociation

Using phase microscopy the behaviour of living neurons directly after their enzymatic isolation from ganglia of Clione limacina and Lymnaea stagnalis was studied. Apart from single-processed unipolar neurons, numerous dipolar and unipolar ones were found in mollusc which does not conform to neuron classification generally adopted. Disrupted neurons were seen to shorten gradually in Ringer solution and -1640 medium at the rate of 0.84-0.27 mm min. Serial photomicrography revealed that the process has two stages. Neurite retraction is interrupted by the expansion stage (extrusion and urgent regeneration). Duration of retraction and extrusion stages made 22.7-3.3 and 6.6-9.1 min respectively. Retraction speed was 24-0.5 mm/min while that of extrusion was 2.8-0.4 mm/min. different processes of the same neuron contract asynchronously. Process invagination leads to its rounding. Thus the cell acquires most thermodynamically stable from which is arranged to prompt its survival. Spherical neurons lacking processes migrate and demonstrate capacity of regeneration. As the conditions somehow resembling the experimental ones (high proteolytic activity of the medium and process loss in part of neurons) arise in cerebral trauma nidus of it is suggested that viable neuron behaviour is alike in this situation.

[FTIR study on structure of pearl and nacre of mollusk shell]

Pearl and nacre of mollusk shell (Hyriopsis cumingii) were studied with high resolution Fourier transformation infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The results of X-ray diffraction indicate that the samples are still aragonite after thermal treatment at 160 degrees C for 5hr, however, the significant variations of peak position and band width of FTIR spectra reveal the interaction between organic matrix and inorganic crystal in biomineralized materials. The variations of spectra were studied by a curve-fitting algorithm and the band related to the interaction is revealed.

[Principles of the structural organization of the chemosensory system of freshwater gastropod mollusks]

Authors own experimental data and data available in literature were summarised to elucidate the influence of the mollusc environment and mode of living on structural organization of tentacular and osphradial systems, receptors of the mouth labia and mantle in typical freshwater mollusc. The similarity between sensory systems of tentacles, mouth and labia was demonstrated based on the findings obtained using silver impregnation, horse radish peroxidase labelling and electron microscopy. Module pattern of organization and peculiarities of sensory organs efferent innervation were demonstrated. Bilateral symmetry and the basis of multichannel structures of sensory systems central regions were described. Specific pattern of structural organization and those common with other animals were shown. The emphasis was made on differences from the olfactory systems of ground gastropods that consist in the lack of olfactory glomeruli, the special olfactory centres, procerebri and specialized chemosensory epithelium in freshwater mollusc.

Structure and function of the Nautilus statocyst

The two equilibrium receptor organs (statocysts) of Nautilus are avoid sacks, half-filled with numerous small, free-moving statoconia and half with endolymph. The inner surface of each statocyst is lined with 130,000-150,000 primary sensory hair cells. The hair cells are of two morphological types. Type A hair cells carry 10-15 kinocilia arranged in a single ciliary row; they are present in the ventral half of the statocyst. Type B hair cells carry 8-10 irregularly arranged kinocilia; they are present in the dorsal half of the statocyst. Both type of hair cells are morphologically polarized. To test whether these features allow the Nautilus statocyst to sense angular accelerations, behavioural experiments were performed to measure statocyst-dependent funnel movements during sinusoidal oscillations of restrained Nautilus around a vertical body axis. Such dynamic rotatory stimulation caused horizontal phase-locked movements of the funnel. The funnel movements were either in the same direction (compensatory funnel response), or in the opposite direction (funnel follow response) to that of the applied rotation. Compensatory funnel movements were also seen during optokinetic stimulation (with a black and white stripe pattern) and during stimulations in which optokinetic and statocyst stimulations were combined. These morphological and behavioural findings show that the statocysts of Nautilus, in addition to their function as gravity receptor organs, are able to detect rotatory movements (angular accelerations) without the specialized receptor systems (crista/cupula systems) that are found in the statocysts of coleoid cephalopods. The findings further indicate that both statocyst and visual inputs control compensatory funnel movements.

Ilyanassa obsoleta (Gastropoda) as a host for trematodes in Delaware estuaries

Extensive data characterizing larval trematode communities in marine gastropods do not exist for many systems. The purpose here is to report on the infections encountered in Delaware Ilyanassa obsoleta and to compare this trematode community with certain others that have been well studied. Over 15 yr, 11,774 I. obsoleta from 9 different estuarine habitats were examined. Trematode parasitism, sex, and size were determined for each snail. In the total collection, 9 trematode species were encountered; 51.04% of snails were infected with 1 or more species. The sexes were equally susceptible to being parasitized. Smaller snails were less likely to be infected than larger ones. Juvenile snails can be infected, but few have been colonized because of the short time they have been exposed to infective stages. Other studies of trematodes in this snail have revealed few multispecies infections. In contrast, they were strikingly common in this study (12.57% of all snails). Himasthla quissetensis seldom infects the same snail with Lepocreadium setiferoides or Austrobilharzia variglandis, but other species combinations can coexist. The important element in this trematode community seems to be time. The observed frequencies of different infracommunities (single and multispecies combinations) in samples of snails are considered to result from a variety of causes. These include commonness of the trematode species in the system, where and how the sample was collected, definitive host behavior, the low probability of a snail becoming infected, the long life of the snail and its infections, the vagility of the snail, and the incompatibility of certain species in terms of infecting the same snail.

Venomous marine animals of Florida: morphology, behavior, health hazards

This article reviews the dangers related to marine animal envenomations in Florida. Venomous marine animals exhibit diverse mechanisms of injury and toxicity. Information regarding the morphology, behavior, and health hazards of these dangerous organisms is presented to help medical personnel recognize, diagnose and treat marine envenomations. Hazardous marine animals discussed in this review include both invertebrates and vertebrates. Stinging invertebrate animals include sponges, coelenterates (jellyfish, hydroids, corals, and sea anemones), echinoderms (sea urchins, starfish and sea cucumbers), annelid worms (bristleworm), and mollusks (cone shells, octopi and nudibranches). Stinging vertebrates discussed include stingrays, catfish, scorpionfish, and leatherjacks.

Serotonin-immunoreactivity in peripheral tissues of the opisthobranch molluscs Pleurobranchaea californica and Tritonia diomedea

The distribution of serotonin (5-HT)-immunoreactive elements in peripheral organs of the sea-slugs Pleurobranchaea californica and Tritonia diomedea was studied in cryostat sections. For Pleurobranchaea, 5-HT-immunoreactive (5-HT-IR) neuron cell bodies were found only in the central nervous system (CNS); 5-HT-IR cell bodies were not observed in foot, tentacles, rhinophores, oral veil, mouth, buccal mass, esophagus, gills, salivary glands, skin, reproductive system, and acidic glands, nor in peripheral tentacle and rhinophore ganglia. However, 5-HT-IR neuronal processes were widely distributed in these structures and the patterns of 5-HT-IR elements were characteristic for each particular peripheral tissue. 5-HT-IR elements were most dense in the sole of the foot and the reproductive system, followed by rhinophores, tentacles, oral veil, mouth, buccal mass, and esophagus. The sensory epithelium of rhinophores, tentacles, and mouth showed a highly structured glomerular organization of 5-HT-IR fibers, suggesting a role for 5-HT in sensory signaling. A much lower density of 5-HT-IR innervation was observed in gills, skin, salivary, and acidic glands. 5-HT-IR was observed in neuropil of tentacle and rhinophore ganglia with many transverse 5-HT-IR axons running to peripheral sensory areas. The distribution of 5-HT-IR elements in Tritonia was similar to that of Pleurobranchaea. A significant suggestion of the data is that central serotonergic neurons may modulate afferent pathways from sensory epithelia at the periphery.

Subcellular localization and function of melanogenic enzymes in the ink gland of Sepia officinalis

The ink gland of the cuttlefish Sepia officinalis has traditionally been regarded as a convenient model system for investigating melanogenesis. This gland has been shown to contain a variety of melanogenic enzymes including tyrosinase, a dopachrome-rearranging enzyme and peroxidase. However, whether and to what extent these enzymes co-localize in the melanogenic compartments and interact is an open question. Using polyclonal antibodies that recognize the corresponding Sepia proteins, we have been able to demonstrate that peroxidase has a different subcellular localization pattern from tyrosinase and dopachrome-rearranging enzyme. Whereas peroxidase is located in the rough endoplasmic reticulum and in the matrix of premelanosomes and melanosomes, tyrosinase and dopachrome-rearranging enzyme are present in the rough endoplasmic reticulum-Golgi transport system, at the level of trans-Golgi cisternae, trans-Golgi network and coated vesicles, and in melanosomes on pigmented granules. These results fill a longstanding gap in our knowledge of the melanin-producing system in Sepia and provide the necessary background for dissection at the molecular level of the complex interaction between melanogenic enzymes. Moreover, the peculiar and complex organization of melanin in an invertebrate such as Sepia officinalis is surprising and could provide the basis for understanding the process in more evolved systems such as that of mammals.

Bacterial endosymbionts in the gills of the deep-sea wood-boring bivalves Xylophaga atlantica and Xylophaga washingtona

Bacterial endosymbionts found in gill tissues in several bivalve families convert otherwise unavailable energy sources (sulfide, methane, or cellulose) to forms readily metabolized by their hosts. We investigated the existence of such a symbiosis in two species of Xylophaga (family Pholadidae). The genus Xylophaga includes opportunistic species that are the predominant colonizers of wood at depths greater than 150 m. It has been hypothesized that, like their shallow-water counterparts the shipworms (family Teredinidae), species of Xylophaga utilize wood for nutrition. Results from transmission and scanning electron microscopy of X. atlantica and X. washingtona clearly demonstrate the presence of endosymbionts that resemble the shipworm endosymbionts both morphologically and in their anatomical location within the gills. Xylophaga and the teredinids both have a caecum packed with wood chips but lack the dense populations of microorganisms associated with cellulose digestion in termites or ruminants. These observations suggest that Xylophaga has evolved a symbiotic solution to wood digestion similar to that seen in shipworms. Hence, the Xylophaga symbiosis suggests a mechanism for the conversion of terrestrially derived cellulosic carbon from wood into animal biomass in the deep sea.

[Karyologic study of gill neoplasia in Macoma balthica (Mollusca, Bivalvia)]

This paper reports the first karyological study of a gill neoplasia in the bivalve Macoma balthica from the Bay of Gdansk (Poland). Chromosomes were studied with an air-drying technique from gill tissue. Out of 47 specimens studied, 34 showed normal cells and a variable number of mitotic metaphases with a normal diploid chromosome number of 2n = 38, 6 had hypertrophied nuclei and a high number of mitoses with 70 to 98 chromosomes, and 7 specimens showed intermediate features. The karyotype of normal metaphases included 11 metacentric, 2 submetacentric and 6 subtelocentric chromosome pairs. The karyotype of abnormal metaphases, i.e. with a high number of chromosomes, revealed chromosomal aberrations inferring neoplastic disorders such as: different number of metacentric, submetacentric, subtelocentric and telocentric chromosome pairs than in the normal karyotype, increase of chromosome pairs especially in the small and medium-sized chromosomes, irregular monosomy and occurrence of microchromosomes. According to neoplasias recorded in bivalves species, the prevalence observed in this neoplasia is relatively high. As Macoma balthica inhabits the polluted Bay of Gdansk, the effects of environmental parameters should be elucidated.

Putative neuroendocrine cells in the Aplysia cerebral ganglion

We report on a special population of cells in the Aplysia cerebral ganglion that are characterized by several features compatible with neuroendocrine function. These cells can be recognized in living ganglia by their small size, white color and their typical distribution as a compact cluster in the central medial region of the dorsal ganglion surface. Upon intracellular recording, these cells generate action potentials of relatively long duration (about 25 ms), as compared with the faster action potentials of larger white cells or of non-white cells (about 4 ms). Intracellular injection of the small white cells with Lucifer yellow after recording revealed a dual projection area: single cells have one process which branches extensively into many varicose terminals as it courses through the neuropil, and then sends varicose terminals to the vascular sheath at the periphery of the ganglion. In cryostat sections, these cells were specifically characterized by their content of large granules, the staining characteristics of which distinguish them from lipochondria or lysosomes. Their ability to bind fluorochromes nonspecifically is of particular importance for the interpretation of histochemical localization studies based on immunofluorescence techniques.

Immunocytochemical reaction of a haemocyanin antibody in the midgut gland of Nautilus (Cephalopoda, Tetrabranchiata)

The branchial gland of the dibranchiate cephalopods is described as the site of haemocyanin synthesis. Because there is no equivalent to this organ in tetrabranchiate cephalopods the localization of haemocyanin synthesis remained unknown for a long time. In this study we could confirm the conclusions from preliminary investigations concerning the copper content of the midgut gland of Nautilus, which gave the first indications for a possible localization of haemocyanin synthesis in this organ. We developed a polyclonal antibody against Nautilus haemocyanin, tested its specificity, and used it on ultra-thin sections of the tissue of the midgut gland. It could be shown that there is a clear immunogold precipitation only on the triangular basal cells in the terminal alveoli. All the other types of cell in this organ were free of any immunoreactivity. It can be supposed that the triangular basal cells in the terminal alveoli of the midgut gland are the sites of haemocyanin synthesis in Nautilus.