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PubMed1984

Succinate dehydrogenase in various tissues of Anodonta couperiana, Elliptio buckleyi and Mercenaria campechiensis (Mollusca: Bivalvia).

The specific activities, kinetic constants and pH optima for succinate dehydrogenase were determined in mantle, gill and adductor muscle from three bivalves (Anodonta couperiana, Elliptio buckleyi and Mercenaria campechiensis). In general the Km values for succinate and Ki values for fumarate differed in all bivalve tissues whereas the Ki for malonate was consistently low. The ratio of Ki (fumarate) to Km (succinate) was less than one for all tissues studied. This is similar to many facultative anaerobes with fumarate reductase activity.

Animals↗
PubMed1996

Organiser role of the stem cell of the mesoderm in prototroch patterning in Patella vulgata (Mollusca, Gastropoda).

During early development of the gastropod mollusc Patella vulgata, the stem cell of the mesoderm (3D-macromere) is induced. As a result of this induction, the embryo becomes dorsoventrally organised. At about the same time in development, ciliated cells, so-called trochoblasts, are formed. Later in development, some trochoblasts deciliate and, together with the ciliated trochoblast, form the dorsoventrally organised prototroch, the locomotory organ of the larva. In order to study the role of the 3D-macromere in the specification of trochoblasts and in the induction of the dorsoventral organisation of the prototroch, induction of 3D has been prevented in various ways. it is shown that preventing 3D-induction results in the formation of a radially symmetrical prototroch. The trochoblasts of all four quadrants developed like corresponding trochoblasts of the A-quadrant. Somewhere between 30 and 120 min after fifth cleavage the 3D-macromere induces the formation of specific trochoblasts and organises the dorsoventral pattern of the prototroch. Besides a role of the 3D-macromere, a role of other cells has been demonstrated in the conditionally specified deciliation of trochoblasts.

Animals↗
PubMed2005

Self-organisation of nacre in the shells of Pterioida (Bivalvia: Mollusca).

Changes in the morphology and orientation of crystals have been tracked across the nacreous layer in pterioid bivalves, by SEM and X-ray diffraction. Early crystals nucleated on the organic membrane usually covering the outer prismatic layer. They formed polycrystalline aggregates of various shapes, first at prism boundaries and progressively invading the prisms in a centripetal fashion. Their c-axes were perpendicular to the substrate, but the a- and b-axis were variously arranged. As they grew, nacreous crystals became individualized and acquired a common crystallographic orientation also in the a-b plane (with the b-axis in the direction of shell growth). Initial lamellae had well delineated growth fronts, which later changed to diffuse. The increasing orientation was explained by a competition model between nacreous plates within the growing lamellae, which was particularly effective in lamellae with delineated fronts. This competition between adjacent crystals could not take place in gastropod nacre because, contrary to the stepped mode of growth of bivalve nacre, vertical stacking predominated. Our model is an alternative to the heteroepitaxial model where the organic matrix supposedly acted as an orienting template, but is nevertheless compatible with the mineral bridge hypothesis that implied epitaxial growth of stacking nacreous tablets.

Animals↗
PubMed2004

Serotonergic regulation of the central heart auricles of Sepia officinalis L. (Mollusca, Cephalopoda).

In pharmacological bioassays on isolated isotonically suspended auricles of Sepia officinalis, the regulatory action of the neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) on these autonomous contractile compartments was demonstrated. 5-HT induced concentration-dependent positive effects on frequency and tone, whereas the concentrations/response curve for the amplitude showed a biphasic course. All applied antagonists inhibited mainly the effect of 5-HT on frequency and amplitude. The chronotropic effects of 5-HT were blocked mainly by the 5-HT(1,2) antagonist methiothepin (pA(2)=8.01), the 5-HT(1a) antagonist NAN-190 (pA(2)-) and in lesser extent by the 5-HT(1,2) antagonist mianserin (pA(2)=6.81). In the presence of each antagonist applied the 5-HT action on amplitude was transformed into a positive inotropic effect with the maximum under influence of NAN-190 and the 5-HT(2,1c)-antagonist ketanserin. The auricular tone was also influenced by the antagonists and in combination with methiothepin it turned into strong negative tonotropic effect. In addition to the pharmacological bioassays, the presence of 5-HT in nerve endings within the auricle wall was demonstrated by immunohistochemical and fluorescence microscopic findings. Altogether the findings presented here confirm that 5-HT evokes excitatory effects on the autonomous contractile auricle of S. officinalis and acts obviously over different receptors, whereby a 5-HT(1)- and a 5-HT(2)-like seem to be involved.

Animals↗
PubMed2004

Regulated bradycardia in the pulmonate limpet Siphonaria (Gastropoda: Mollusca) during pollutant exposure: implication for biomarker studies.

Although the cardiac activity of invertebrates is now widely used as a biomarker of marine pollution, few studies consider the intrinsic factors causing the variability of heart rate (HR), including the physiological states associated with metabolic depression and behavioural isolation. We examined the cardiac responses to copper exposure of a pulmonate limpet (Siphonaria capensis Quoy and Gaimard), known to adaptively depress heart rate (and metabolic rate) under naturally stressful conditions (hyposalinity). Analysis of variance was used to assess the effects of copper concentration (0-1000 microg/L), exposure time (0-2 h), and individual difference (eight limpets per concentration) on heart rate parameters. Minute by minute heart rate (HR) and heart rate variability (HRV), and bradycardia (< or =10 beats/min) were determined from continuous recording traces. Most of the HR variance was attributable to the interaction of concentration and individuals (35.8%). Considerably lower mean HRs for the higher range of copper concentrations (250 to 1000 microg/L), compared to the lower range (0 to 50 microg/L), were attributable to the virtually exclusive induction of bradycardia in the higher concentration treatments. With increasing concentration, bradycardia was induced sooner and became less interspersed with near normal heart rates (i.e., less episodic). This regulated bradycardial response is apparently associated with isolation (avoidance) behaviour rather than with copper uptake. These findings have implications for biomarker exercises which use heart rate, in cases where invertebrates depress metabolism.

Animals↗
PubMed2005

Light and electron microscopy studies of the oesophagus and crop epithelium in Aplysia depilans (Mollusca, Opisthobranchia).

The oesophagus and crop epithelium of Aplysia depilans consist in a single layer of columnar cells with apical microvilli, and some of them also possess cilia. Cell membrane invaginations, small vesicles, multivesicular bodies and many dense lysosomes were observed in the apical region of the cytoplasm. In most cells, a very large lipid droplet was observed above the nucleus and a smaller one was frequently found below the nucleus; glycogen granules are also present. Considering these ultrastructural features, it seems that these cells collect nutritive substances from the lumen by endocytosis, digest them in the apical lysosomes and store the resulting products. The cell bodies of mucus secreting flask-shaped cells are subepithelial in the oesophagus and intraepithelial in the crop. Histochemistry methods showed that the secretion stored in these cells contains acidic polysaccharides. Secretory vesicles with thin electron-dense filaments scattered in an electron-lucent background fill most of these cells, and the basal nucleus is surrounded by dilated rough endoplasmic reticulum cisternae containing small tubular structures. Considering the relatively low number of secretory cells, mucus production cannot be high. Moreover, since protein secreting cells were not observed in either oesophagus or crop, extracellular digestion in the lumen of these anterior segments of the digestive tract most probably depend on the enzymes secreted by the salivary and digestive glands.

Animals↗
PubMed2004

Molecular phylogeny of the family Pectinidae (Mollusca: Bivalvia) based on mitochondrial 16S and 12S rRNA genes.

Pectinidae is a large bivalve family characterised by almost circular, flat shells. Species are distributed worldwide and fall into three life-styles: swimming, byssally attached to hard substrates, and cemented to rocks with one valve. Despite these very different life strategies, pectinid shells are highly conservative in shape and offer few clues for the unravelling of phylogenetic issues. Consequently, phylogenetic studies based on morphological features have not yielded conclusive results. We thus set out to analyse partial sequences of mitochondrial 12S and 16S rRNA genes from 23 species of 16 genera with molecular techniques. The results are largely in contrast, both at the genus and the subfamily level, with the systematic classifications based on adult morphological characters, whereas they agree with the morphological classifications based on the more conserved non-adaptive features.

Animals↗
PubMed1983

An ultrastructural analysis of Dentalium vulgare (Mollusca, Scaphopoda) gametes with special reference to early events at fertilization.

The ultrastructure of Dentalium gametes, and their fate at fertilization, were investigated. Unexpectedly, fixation carried out in 2% osmium tetroxide, at 4 degrees C, although destroying most cytoplasmic organelles, reveals the presence of bundles of "stress fibers" in the microvilli and the fertilization cone of the eggs. Anti-actin labeling supports the view that the bundles are made of actin. Fertilization, as in other molluscs, does not cause any cortical granule exocytosis, at least during the first 15 min following insemination. Ultrastructure of the unreacted and reacted spermatozoon is presented and a tentative model for the morphological interpretation of the acrosomal reaction is proposed. A reevaluation of cytoplasmic heterogeneity, e.g., the so-called cytoplasmic prelocalization, as observed after the germinal vesicle breakdown is also provided as well as an analysis of concomitant surface changes.

Acrosome↗