Shell nacre ultrastructure and depressurisation dissolution in the deep-sea hydrothermal vent mussel <Emphasis Type="Italic">Bathymodiolus azoricus</Emphasis>

This study describes the micro-morphological features of the shell nacre in the vent mytilid Bathymodiolus azoricus collected along a bathymetric gradient of deep-sea hydrothermal vents of the mid-Atlantic ridge (MAR). Pressure-dependent crystallisation patterns were detected in animals subjected to post-capture hydrostatic simulations. We provide evidence for the following: (1) shell micro morphology in B. azoricus is similar to that of several vent and cold-seep species, but the prismatic shell layers may vary among bathymodiolids; (2) nacre micro-morphology of mussels from three vent sites of the MAR did not differ significantly; minor differences do not appear to be related to hydrostatic pressure, but rather to calcium ion availability; (3) decompression stress may cause drop off in pH of the pallial fluid that damages nascent crystals, and in a more advanced phase, the aragonite tablets as well as the continuous layer of mature nacre; and (4) adverse effects of decompression on calcium salt deposition in shells was diminished by re-pressurisation of specimens. The implications of the putative influence of hydrostatic pressure on biomineralisation processes in molluscs are discussed.     

The Micro/Nanostructure Characteristics and the Mechanical Properties of Hemifusus tuba Conch Shell

<正> The mollusk shell mobilizes calcium from environment for skeletal mineralization.This occurs through synthesizing solidsin solution in the presence of organic molecules of specific interior regions of the conch shell.The ultrastructure and microhardnessof the Hemifusus tuba conch shell living in the Huang/Bo sea area are investigated in the paper.It is shown that thecomposition and microstructure of the mollusk shell vary in different positions.The prodissoconch shell consists only of aragonitewith the crossed-lamellar microstructure.While the spiral shell and the body shell of the Hemifusus tuba conch shell arecomposed of one calcite layer and several aragonite layers.The calcite layer consists of cylindrical grains,but the aragonitelayers are crossed-lamellar ultrastructure at three size scales.The minimum structure size (the third-order lamella) is at about20 nm - 80 nm.The margin of shell aperture is only composed of calcite with cylindrical grains.This natural optimization of theshell microstructure is intimately due to the growth of the Organic matrix.At different positions the microhardness of molluscshell is different due to different crystal structures and crystal arrangements.The growth process of shells allows a constantrenewal of the material,thus enabling their functional adaptation to external environments.     

Ligamental increments of the mid-Holocene Pacific oyster Crassostrea gigas are reliable independent proxies for seasonality in the western Bohai Sea,China

Modern living and mid-Holocene shells of Crassostrea gigas from the western Bohai Sea in China were subjected to sclerochronological analysis with the aim of determining whether their concave bottoms and growth breaks on resilifer surfaces, as well as corresponding translucent growth bands visible in cross-section, have seasonal significance. An additional aim was to obtain ontogenetic information from mid-Holocene fossil shells. We compared δ¹⁸O and δ¹³C profiles compiled with high and low sampling resolution for the same shell in order to test the consistency of the results and identify a suitable sampling strategy for future sclerochronological studies. The results show that concave bottoms on the resilifer surface and corresponding translucent growth bands in cross-section formed during the cold season. These features are appropriate indicators of annual growth increments in fossil C. gigas shells. Moreover, growth breaks located near convex tops indicate annual growth increments for that part of the shell which grew when the organism was sexually mature. Therefore, spawning-related growth breaks and alternating winter freeze shocks (concave bottoms) are excellent morphological features in determining annual growth increments. Consequently, the life span, growth rate, and timing of spawning and death can be determined from the increments of ligament growth of these fossil oyster shells. For future sclerochronological studies, an adaptive micro-sampling strategy could be used for different increments of ligament growth that represent different seasons. Such a strategy would be more efficient in providing reliable insights into growth history of shells with variable growth rates of annual increments.     

Correlation of stable oxygen isotope temperature record with light attenuation profiles in reef-dwellingTridacna shells

Molluscs are known to record environmental changes in their carbonate shells in detail. This paper reports the findings of a high-resolution analysis of stable oxygen isotopic compositions and light transmission properties of a shell of the reef-dwelling Pacific giant clamTridacna gigas. Our findings reveal that the annual growth rates and the longevity ofTridacna specimens can be readily determined by measuring the annual light attenuation pattern within the shell. Annual seasonal changes in water temperature are reflected with high resolution in the stable oxygen isotope ratios and in the light attenuation values of the aragonite shell. The inner shell ofT. gigas deposited below the pallial line revealing undisturbed shell accretion with high growth rates shows the maximum seasonal oxygen isotope range and the highest resolution in light attenuation changes. We suggest that this is the best part of the shell to reconstruct former seasonal surface water temperatures in tropical environments. Scanning electron microscopy (SEM) studies suggest that the annual growth patterns observed in transmitted light are generated by a complex pattern of daily growth increments with varying sizes of skeletal crystallites and varying amounts of organic carbon.     

Structure and composition of the boundary zone between aragonitic crossed lamellar and calcitic prism layers in the shell of Concholepas concholepas (Mollusca,Gastropoda)

Mollusc shells are composed of two or three layers. The main layers are well‐studied, but the structural and chemical changes at their boundaries are usually neglected. A microstructural, mineralogical, and biochemical study of the boundary between the inner crossed lamellar and outer prismatic layers of the shell of Concholepas concholepas showed that this boundary is not an abrupt transition. Localized structural and chemical analyses showed that patches of the inner aragonitic crossed lamellar layer persist within the outer calcitic prismatic layer. Moreover, a thin aragonitic layer with a fibrous structure is visible between the two main layers. A three‐step biomineralization process is proposed that involves changes in the chemical and biochemical composition of the last growth increments of the calcite prisms. The changes in the secretory process in the mantle cells responsible for the shell layer succession are irregular and discontinuous.     

Calcite crystal orientation patterns in the bilayers of laminated shells of benthic rotaliid foraminifera

Shells of calcifying foraminifera play a major role in marine biogeochemical cycles; fossil shells form important archives for paleoenvironment reconstruction. Despite their importance in many Earth science disciplines, there is still little consensus on foraminiferal shell mineralization. Geochemical, biochemical, and physiological studies showed that foraminiferal shell formation might take place through various and diverse mineralization mechanisms.In this study, we contribute to benthic foraminiferal shell calcification through deciphering crystallite organization within the shells. We base our conclusions on results gained from electron backscattered diffraction (EBSD) measurements and describe microstructure/texture characteristics within the laminated shell walls of the benthic, symbiontic foraminifera: Ammonia tepida, Amphistegina lobifera, Amphistegina lessonii. We highlight crystallite assembly patterns obtained on differently oriented cuts and discuss crystallite sizes, morphologies, interlinkages, orientations, and co-orientation strengths.We show that: (i) crystals within benthic foraminiferal shells are mesocrystals, (ii) have dendritic-fractal morphologies and (iii) interdigitate strongly. Based on crystal size, we (iv) differentiate between the two layers that comprise the shells and demonstrate that (v) crystals in the septa have different assemblies relative to those in the shell walls. We highlight that (vi) at junctions of different shell elements the axis of crystal orientation jumps abruptly such that their assembly in EBSD maps has a bimodal distribution. We prove (vii) extensive twin-formation within foraminiferal calcite; we demonstrate (viii) the presence of two twin modes: 60°/[0 0 1] and 77°/~[6 –6 1] and visualize their distributions within the shells.In a broader perspective, we draw conclusions on processes that lead to the observed microstructure/texture patterns.     

Variability of shell repair in the Manila clam Ruditapes philippinarum affected by the Brown Ring Disease: a microstructural and biochemical study

For more than two decades, the Manila clam Ruditapes philippinarum has been regularly affected by Brown Ring Disease (BRD), an epizootic event caused by the bacterium Vibrio tapetis and characterized by the development of a brown deposit on the inner face of valves. Although BRD infection is often lethal, some clams recover by mineralizing a new repair shell layer, which covers the brown deposit and fully isolates it from living tissues. In order to understand this specific shell repair process, the microstructures of repaired zones were compared to those of shells unaffected by BRD. In addition, the organic matrix associated with unaffected shells and to repair patches were extracted and compared by biochemical and immunological techniques. Our results show that the repaired zones exhibit microstructures that resemble the so-called homogeneous microstructure of the internal layer, with some marked differences, like the development of crossed-acicular crystals, which form chevron-like patterns. In the three tested batches of repaired layers, the matrices exhibit certain heterogeneity, i.e., they are partially to widely different from the ones of shells unaffected by BRD, as illustrated by SDS-PAGE and by serological comparisons. Our results strongly suggest a modification of the secretory regime of calcifying mantle cells during the shell repair process. Polyclonal antibodies, which were developed against specific protein fractions of the shell, represent relevant tools for localizing by immunohistology the cells responsible for the repair.     

Shell extracts of the edible mussel and oyster induce an enhancement of the catabolic pathway of human skin fibroblasts,in vitro

Mollusc shells are composed of more than 95% calcium carbonate and less than 5% organic matrix consisting mostly of proteins, glycoproteins and polysaccharides. In this study, we investigated the effects of matrix macromolecular components extracted from the shells of two edible molluscs of economic interest, i.e., the blue mussel Mytilus edulis and the Pacific oyster Crassostrea gigas. The potential biological activities of these organic molecules were analysed on human dermal fibroblasts in primary culture. Our results demonstrate that shell extracts of the two studied molluscs modulate the metabolic activities of the cells. In addition, the extracts caused a decrease of type I collagen and a concomitant increase of active MMP-1, both at the mRNA and the protein levels. Therefore, our results suggest that shell extracts from M. edulis and C. gigas contain molecules that promote the catabolic pathway of human dermal fibroblasts. This work emphasises the potential use of these shell matrices in the context of anti-fibrotic strategies, particularly against scleroderma. More generally, it stresses the usefulness to valorise bivalve shells that are coproducts of shellfish farming activity.     

Comparison of bioethanol production from cultivated versus wild <Emphasis Type="Italic">Gracilaria verrucosa</Emphasis> and <Emphasis Type="Italic">Gracilaria gigas</Emphasis>

The seaweed genus Gracilaria is a potential candidate for the production of bioethanol due to its high carbohydrate content. Gracilaria is abundant throughout the world and can be found in both wild and cultivated forms. Differences in the ecological factors such as temperature, salinity, and light intensity affecting wild and cultivated specimens may influence the biochemical content of seaweeds, including the carbohydrate content. This study aimed to investigate the proximate composition and potential bioethanol production of wild and cultivated G. gigas and G. verrucosa. Bioethanol was produced using separate hydrolysis fermentation (SHF), employing a combination of enzymatic and acid hydrolysis, followed by fermentation with Saccharomyces cerevisiae ATCC 200062. The highest carbohydrate content was found in wild G. gigas. The highest galactose and glucose contents (20.21 ± 0.32 and 9.70 ± 0.49 g L^?1, respectively), as well as the highest production of bioethanol (3.56 ± 0.02 g L^?1), were also found in wild G. gigas. Thus, we conclude that wild G. gigas is the most promising candidate for bioethanol production. Further research is needed to optimize bioethanol production from wild G. gigas. Domestication of wild G. gigas is a promising challenge for aquaculture to avoid overexploitation of this wild seaweed resource.     

A scanning electron microscopic study of the inorganic and organic matrices comprising the mature shell of Amblema, a fresh-water mollusc

The scanning electron microscope has been used to describe the morphology of the mature shell in a fresh-water bivalve. The structure of the organic and inorganic components within the nacre, the myostracum, and the prismatic layer is described. A transitional or intermediate zone, interposed between the prismatic layer and the nacre, was identified. In demineralized samples, the organic component of the nacre was found to consist of parallel matricial sheets interconnected by irregular transverse bridges. The structure of the mineral component of the nacre was found to vary with the method of specimen preparation. With polished-etched samples, brick-like units were seen. When shells were simply broken and fixed in osmium, the layers of nacreous material consisted of fusing rhomboidal crystals of aragonite which demonstrated subconchoidal fractures. On the inner surface of the shell, the rhomboidal crystals showed an apparent spiral growth pattern. The myostracum was characterized by regions of modified nacreous structure consisting of enlarged aragonite crystals with a pyramidal morphology. The peripheral aspect of the muscle scars was characterized by rhomboidal crystals, the latter fusing to form the typical nacreous laminae. The uniqueness of the anterior adductor scar is exemplified by the presence of pores, each pore walled by pyramidal units, for the insertion of adductor fibres. In most regions of the shell, the prismatic layer consisted of one prism unit thickness with a height of approximately 225–250 μm. However, in two specialized regions of the shell, this layer was seen to consist of multiple layers of stacked prisms. The organic matrices of the prismatic layer are arranged in a honeycomb-like arrangement and packed with mineralized spherical subunits.     

A study of the egg shells of the Falconiformes

A study of a selection of egg shells of the Falconiformes has been made similar to the earlier ones on ratites, the Anatidae and the Sphenisciformes. Chemical analyses, and histological and plastic embedding techniques were used.
The main part of the shell in all species studied consists of large crystals running through the shell. There was no layer of fine vertical crystals above this and no cover, and even the cuticle was not very pronounced. Histological studies showed no major differences, except that some shells had vacuoles in the outer layers. All such shells also gave an unetched outer layer when plastic embedded radial sections were studied and thin sections showed spaces between and within crystals. These spaces in the outer layers of the shell were of taxonomic interest for they were not present in the Cathartidae, the Falconidae and Sagittarius serpentarius.
Pore channels appeared to be much sparser than in other orders so far studied and all pores were single. Pigment was present on the surface of some shells, but it was also found in different layers of the shell right down to the cone layer and, in one case, had leaked through on to the membrane.
There were significant relationships between total and soluble shell nitrogen which divided the Falconidae from most of the Accipitridae but left Pernis and Pandion in an intermediate position.     

Origin and expansion of foliated microstructure in pteriomorph bivalves

The ultrastructure of the calcitic prisms of the prismatic shell layers of pteriomorph bivalves was examined by scanning electronic microscopy and diffraction techniques. Results indicate that the internal structure of the prisms is noticeably different among taxa. In species belonging to the families Pinnidae, Pteriidae, and Isognomonidae (Pterioida), prisms are built up with nanometric calcite crystals. On the other hand, Pectinidae, Propeamussliidae, Anomiidae (order Pectinoida) and the Ostreidae (Ostreoida) have prisms constituted by calcitic laths with micrometric size. These laths are indistinguishable from those constituting the foliated microstructure. In almost all cases, there is mineral continuity from the prisms to the underlying foliated layer, as confirmed by X-ray texture analyses. These findings corroborate a previous assumption that the foliated microstructure derived from calcitic prisms, particularly from those with internal foliated structure. The appearance of the foliated microstructure facilitated drastic mineralogical and microstructural changes in pteriomorph shells-for example, the development of rigid shell margins and the production of largely calcitic shells. Such changes have, no doubt, contributed to the evolutionary success of the groups, which have shown a pronounced diversification over time.     

Estimates of Heritability for Growth and Shell Color Traits and Their Genetic Correlations in the Black Shell Strain of Pacific Oyster <Emphasis Type="Italic">Crassostrea gigas</Emphasis>

The Pacific oyster Crassostrea gigas has been introduced widely and massively and became an economically important aquaculture species on a global scale. We estimated heritabilities of growth and shell color traits and their genetic correlations in black shell strain of C. gigas. Analyses were performed on 22 full-sib families in a nested mating design including 410 individuals at harvest (24 months of age). The parentage assignment was inferred based on four panels of multiplex PCR markers including 10 microsatellite loci and 94.9% of the offspring were unambiguously assigned to single parent pairs. The Spearman correlation test (r = ? 0.992, P < 0.001) demonstrated the high consistency of the shell pigmentation (SP) and L* and their same efficacy in shell color measurements. The narrow-sense heritability estimated under the animal model analysis was 0.18 ± 0.12 for shell height, 0.25 ± 0.16 for shell length, 0.10 ± 0.09 for shell width, 0.42 ± 0.20 for total weight, 0.32 ± 0.18 for shell weight, and 0.68 ± 0.16 for L*, 0.69 ± 0.16 for shell pigmentation, respectively. The considerable additive genetic variation in growth and shell color traits will make it feasible to produce genetic improvements for these traits in selective breeding program. High genetic and phenotypic correlations were found among growth traits and among shell color traits. To optimize a selection strategy for both fast growth and pure dark shell strain of C. gigas, it is proposed to take both total weight and black shell as joint objective traits in selective breeding program. Our study offers an important reference in the process of selective breeding in black shell color stain of C. gigas and will facilitate to develop favorable breeding strategies of genetic improvements for this economically important strain.     

Aragonitic dendritic prismatic shell microstructure in Thracia (Bivalvia,Anomalodesmata)

The shells of most anomalodesmatan bivalves are composed of an outer aragonitic layer of either granular or columnar prismatic microstructure, and an inner layer of nacre. The Thraciidae is one of the few anomalodesmatan families whose members lack nacreous layers. In particular, shells of members of the genus Thracia are exceptional in their possession of a very distinctive but previously unreported microstructure, which we term herein “dendritic prisms.” Dendritic prisms consist of slender fibers of aragonite which radiate perpendicular to, and which stack along, the axis of the prism. Here we used scanning and transmission electron microscopical investigation of the periostracum, mantle, and shells of three species of Thracia to reconstruct the mode of shell calcification and to unravel the crystallography of the dendritic units. The periostracum is composed of an outer dark layer and an inner translucent layer. During the free periostracum phase the dark layer grows at the expense of the translucent layer, but at the position of the shell edge, the translucent layer mineralizes with the units typical of the dendritic prismatic layer. Within each unit, the c‐axis is oriented along the prismatic axis, whereas the a‐axis of aragonite runs parallel to the long axis of the fibers. The six‐rayed alignment of the latter implies that prisms are formed by {110} polycyclically twinned crystals. We conclude that, despite its distinctive appearance, the dendritic prismatic layer of the shell of Thracia spp. is homologous to the outer granular prismatic or prismatic layer of other anomalodesmatans, while the nacreous layer present in most anomalodesmatans has been suppressed.     

Preboreal oscillations inferred from Arctica islandica sclerochronology

An increasingly important source of annually resolved palaeoenvironmental proxy data originates from cross-dated incremental chronologies summarizing the shell growth of several individuals. Here, we have analysed annual increment variations in a collection of radiocarbon-dated shells of ocean quahog (Arctica islandica) from early Holocene prodelta deposits in north Norway. Radiocarbon dating of the shell material showed that the increments were formed contemporaneously during Preboreal times. The biologically youngest shell contains 35 annual increments, whereas the oldest shell shows 169 increments. Time-series of annual increments demonstrated clear age trends with the widest increments during the very early years of bivalve life, followed by a notable decline in increment widths as the bivalves aged. Subsequent to removing these biological trends from the series, a sclerochronological cross-dating was carried out and resolved the temporal alignments of the shell growth increment records relative to each other. The resulting shell growth increment chronology evidences vigorous growth variations. Spectral analysis of the chronology revealed 3.7- and 4.3-year periodicities, indicative of Preboreal environmental oscillations. Periodicities of longer period were not detected. Our results prove the value of radiocarbon-dated shell assemblages to build “floating” geochronologies for periods and regions where dead shells from museum collections or seabed are not obtainable. Increasing constructions of such chronologies enhance the potential of sclerochronological cross-dating of annual shell growth increment chronologies to depict and detail annually-resolved climate variability not only for late Holocene, as previously illustrated, but also for early Holocene times, when large-scale oscillations punctuated the global climate dynamics. Development of longer chronologies with higher sample replication remains an attainable interdisciplinary target.     

Über parasitische Polychaeten in Kreide-Austern sowie einige andere in Muschelschalen bohrende Würmer

Shells of oysters from Turonian strata in Westphalia contain dwelling tubes of polychaete worms sunk into the shell material. The roofs of the tubes consist of shell material secreted by the oysters. Thus the tubes are intra vitam deformations of the shell, resembling the “mudblisters” of recent oysters. Usually, they are directed centripetally towards the muscle scar and have a round external opening perforating the shell. They are described asOstreoblabe perforans n. g. n. sp. Since they were probably oriented with their front part toward the inside of the shell, penetrating the pallial line, they were most likely parasites. In addition, long, meandering furrows sunk into the shells of pelecypods are described asMaeandropolydora decipiens n. g. n. sp. andM. sulcans n. g. n. sp. The realPolydora is not found in Pre-Tertiary strata and is probably not related genetically toPolydora-like forms (Caulostrepsis) in Devonian strata.     

Age and growth rate determinations of an intertidal bivalve, Phacosoma japonicum, using internal shell increments

A venerid bivalve Phacosoma japonicum (Reeve) occurring commonly in the Japanese coastal area preserves periodic growth lines in the shell cross-section. Long-term shell growth patterns of this species have been traced for many individuals on the intertidal flat of the Seto Inland Sea, west Japan. Sclerochronological analysis of these individuals and specimens collected monthly shows that several growth cessation marks within their shells are formed during the winter of each year prior to spawning. Hence the marks were used for age and growth rate determinations. As large individuals showed little shell growth for more than two years after the formation of 7 or 8 annual increments, this species probably has a lifespan of more than ten years. Shell growth patterns of this species based on annual increments can be accurately approximated by a von Bertalanffy curve. The number of microgrowth increments formed during a year tends to decrease with age, although it varies markedly among specimens of the same age. Furthermore, even in summer during rapid shell growth, the microgrowth increments do not represent daily and/or sub-daily tidal rhythms in many specimens. The results of this study and those by several authors strongly suggest that the annual increments are the key for age and growth rate determinations of both living and fossil bivalve species.     

Shell microstructure of <Emphasis Type="Italic">Discinisca suborbicularis</Emphasis> sp. nov. (Brachiopoda,Lingulata) from the Upper Jurassic of Western Siberia

A new species of the phosphatic brachiopod Discinisca suborbicularis (family Discinidae) from the Upper Jurassic of Western Siberia (latitudinal Priob’e) is established. The shell microstructure under protegulum and brephic shell and the microstructure of adult shell (that corresponds to three developmental stages) are described in detail. The shell microstructure of new species considerably differs from Paleozoic discinids and is similar to Recent discinids. D. suborbicularis differs from recent discinids in the presence of protegulum and thicker organophosphatic primary layer.     

<Emphasis Type="Italic">Hypoanthraconaia</Emphasis>: a new genus of non-marine bivalve molluscs from the Early Permian of Far East Russia

Early Permian continental deposits include a large number of localities containing anthracosiid-like non-marine bivalves traditionally assigned to Anthraconaia Trueman and Weir, 1946, Palaeanodonta Amalitzky, 1895, and Palaeomutela Amalitzky, 1892. In most cases, these classifications are only tentative due to insufficient preservation in which the shells are missing their main characteristics: the ligament and the hinge. Non-marine bivalves from the Early Permian Upper Pospelovka Subformation of Russky Island (South Primorye, Far East Russia), described here as Hypoanthraconaia gen. nov., differ morphologically from the above genera by a set of external features including the initial shell, the mode of intersection of the growth lines with the dorsal margin, and the details of the sculpture. Hypoanthraconaia gen. nov. shows the most external similarity with “atypical” anthracosiid-like morphotypes of Anthraconaia that are widespread in the Late Pennsylvanian and Early Permian of eastern North America, and the Stephanian and Early Permian Lower Rotliegend of northwestern Europe. On this basis, the new genus is conventionally assigned to the family Naiaditidae Scarlato and Starobogatov, 1979.     

A Glycoprotein in Shells of Conspecifics Induces Larval Settlement of the Pacific Oyster Crassostrea gigas

Settlement of larvae of Crassostrea gigas on shell chips (SC) prepared from shells of 11 different species of mollusks was investigated. Furthermore, the settlement inducing compound in the shell of C. gigas was extracted and subjected to various treatments to characterize the chemical cue. C. gigas larvae settled on SC of all species tested except on Patinopecten yessoensis and Atrina pinnata. In SC of species that induced C. gigas larvae to settle, settlement was proportionate to the amount of SC supplied to the larvae. When compared to C. gigas SC, all species except Crassostrea nippona showed lower settlement inducing activities, suggesting that the cue may be more abundant or in a more available form to the larvae in shells of conspecific and C. nippona than in other species. The settlement inducing activity of C. gigas SC remained intact after antibiotic treatment. Extraction of C. gigas SC with diethyl ether (Et₂O-ex), ethanol (EtOH-ex), and water (Aq-ex) did not induce larval settlement of C. gigas larvae. However, extraction of C. gigas SC with 2N of hydrochloric acid (HCl-ex) induced larval settlement that was at the same level as the SC. The settlement inducing compound in the HCl-ex was stable at 100°C but was destroyed or degraded after pepsin, trypsin, PNGase F and trifluoromethanesulfonic acid treatments. This chemical cue eluted between the molecular mass range of 45 and 150 kDa after gel filtration and revealed a major band at 55 kDa on the SDS-PAGE gel after staining with Stains-all. Thus, a 55 kDa glycoprotein component in the organic matrix of C. gigas shells is hypothesized to be the chemical basis of larval settlement on conspecifics.