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Microstructure and texture patterns of molluse shells
... The main conclusion is that the fibrous prismatic layer of mytilids is a perfectly organized material, which displays a sheet texture (i.e., the crystallographic axes are evenly aligned in the three directions perpendicular to the caxis). Some microstructures display fibre textures, with the caxes of either calcite (e.g., prismatic calcite; Checa & Rodríguez-Navarro, 2005;Checa et al., 2005) or aragonite crystals (granular homogeneous, gastropod nacre and Nautilus; Hedegaard & Wenk, 1998;Chateigner et al., 2000Chateigner et al., , 2002Harper et al., 2009) being parallel, but with the rest of the axes rotated. Sheet textures have been described in the nacres of bivalves and Nautilus (Wada, 1961;Wise, 1970;Hedegaard & Wenk, 1998;Chateigner et al., 2000;Checa & Rodríguez-Navarro, 2005), the crossed lamellar microstructures of bivalves and gastropods (Hedegaard & Wenk, 1998;Chateigner et al., 2000) and in the foliated calcite of ostreoids and pectinoids (Checa et al., 2007). ...
... Some microstructures display fibre textures, with the caxes of either calcite (e.g., prismatic calcite; Checa & Rodríguez-Navarro, 2005;Checa et al., 2005) or aragonite crystals (granular homogeneous, gastropod nacre and Nautilus; Hedegaard & Wenk, 1998;Chateigner et al., 2000Chateigner et al., , 2002Harper et al., 2009) being parallel, but with the rest of the axes rotated. Sheet textures have been described in the nacres of bivalves and Nautilus (Wada, 1961;Wise, 1970;Hedegaard & Wenk, 1998;Chateigner et al., 2000;Checa & Rodríguez-Navarro, 2005), the crossed lamellar microstructures of bivalves and gastropods (Hedegaard & Wenk, 1998;Chateigner et al., 2000) and in the foliated calcite of ostreoids and pectinoids (Checa et al., 2007). Although the case of bivalve nacre was explained by Checa et al. (2006) as being due to competition between nacre platelets, this model cannot be universal, because it only applies when nacre plates are elongated along the b-axis. ...
... Some microstructures display fibre textures, with the caxes of either calcite (e.g., prismatic calcite; Checa & Rodríguez-Navarro, 2005;Checa et al., 2005) or aragonite crystals (granular homogeneous, gastropod nacre and Nautilus; Hedegaard & Wenk, 1998;Chateigner et al., 2000Chateigner et al., , 2002Harper et al., 2009) being parallel, but with the rest of the axes rotated. Sheet textures have been described in the nacres of bivalves and Nautilus (Wada, 1961;Wise, 1970;Hedegaard & Wenk, 1998;Chateigner et al., 2000;Checa & Rodríguez-Navarro, 2005), the crossed lamellar microstructures of bivalves and gastropods (Hedegaard & Wenk, 1998;Chateigner et al., 2000) and in the foliated calcite of ostreoids and pectinoids (Checa et al., 2007). Although the case of bivalve nacre was explained by Checa et al. (2006) as being due to competition between nacre platelets, this model cannot be universal, because it only applies when nacre plates are elongated along the b-axis. ...
The outer layer of the shell of members of the genus Mytilus is made of long, slender fibres of calcite (some 1–2 μm wide and hundreds of μm long), which reach the internal surface of the shell at an angle. This microstructure has been called anvil-type fibrous calcitic and its organization, crystallography and relationships to the organic phase are poorly known. We have studied the outer calcitic layer of the Mediterranean mussel M. galloprovincialis by means of optical and scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction (XRD) and atomic-force microscopy (AFM). SEM data from other species have also been gathered. All data together imply that the material is extremely well ordered both from the morphological and crystallographic viewpoints. The XRD pole figures show that there are discrete 001 and 104 maxima; therefore, the material has a well-defined sheet texture. In living animals there is an organic membrane (surface membrane) that coats the inner surface of the shell. TEM sections of the decalcified material show that this mainly proteinaceous surface layer is internally laminated and fills all the spaces left between the growing fibres. Every fibre is a monocrystal with three well developed {104} rhombohedral faces at its growth end. One of these faces is directly in contact with, and strictly parallel, to the sublayers of the surface membrane and thus to the inner shell surface. AFM experiments consisting on growing calcite onto shell pieces in which the surface membranes are preserved, show that the calcitic fibres of the shell easily regrow across the membrane, demonstrating that it is permeable to ions. In this way, prisms are able to grow despite the existence of the intermediate membrane in the living animal. Additional experiments of calcite growth onto the inner side of the surface membrane show that crystals grow onto their {104} surfaces. The surface membrane is responsible for the high degree of ordering of the fibrous calcitic layer, because it stabilizes the orientation of a rhombohedral surface, once this is parallel to the protein sublayers. This is one of the very few cases in which the influence of the organic matter on the organization of microstructures can be demonstrated.
... However, only few papers consider the aggregate properties of shells (Bùggild, 1930;Wenk, 1965;Wilmot et al., 1992). Mutvei (1978Mutvei ( , 1980 hypothesised about the crystallographic properties of nacre tablets, but his conclusions have been at least partly refuted by recent investigations (Hedegaard and Wenk, 1998). ...
... Mutvei (1978Mutvei ( , 1980 observed striations formed by etching on nacre tablets and interpreted them as evidence for individual nacre tablets to be made of cyclic domains, related to each other by a {110} twin, giving rise to the pseudo-hexagonal symmetry of aragonite. Looking at the angles between Mutvei's striations, Hedegaard and Wenk (1998) suggested they may be crystallographically nonequivalent, time-synchronous growth sectors with different composition and solubility. None of the available information, including X-ray texture analysis, allows us to determine whether the individual tablets are single crystals (that may or may not be aligned in a twin-like pattern), a peculiar intergrowth of single twins (Mutvei, 1978(Mutvei, , 1980, pseudohexagonal {110} trillings, or whether even Mutvei's sectors are mosaics of twinned domains and a detailed TEM study would be necessary to resolve this issue. ...
... Bùggild (1930) describes two orientations of optic axes in the second-order lamellae of simple crossed lamellar microstructures indicating that neighbouring lamellae are morphologically and crystallographically identical but rotated 1808 relative to each other. Hedegaard and Wenk (1998) ®nd the two c-axis maxima in the crossed lamellar layers of Scutellastra tabularis and Fragum fragum are inclined about 20±258 to the surface normal and (110) poles aligned perpendicular to the shell margin, correspond-ing to the two dip directions of the lamellae. This indicates that basal planes are parallel to the lamellae. ...
X-ray diffraction is used to characterise textures of the aragonite layers of shells from monoplacophoras, bivalves, cephalopods and gastropods. Textures vary in strength, pattern and through the thickness of the shells. The texture patterns exhibited in the studied taxa, which can be quantitatively described by a limited number of parameters, are compared with the microstructure types observed with scanning electron microscopy. Whereas for simple crystallite arrangements, such as nacres, there is a good correspondence between texture and microstructure, this is often not the case in more complex microstructures such as in crossed lamellar layers. Morphologically similar microstructures may have different crystallographic textures, and the same textures may be found in microstructures with different morphology. These two kinds of measurements are shown to be complementary since they provide non-redundant information for many taxa, which suggests that they may be valuable phylogenetic indicators.
... The EBSD technique has been used to obtain crystallographic texture information about bivalve mollusc shells [11][12][13], and the pole figures for these shells have been measured with X-rays [14]. We use neutron time-offlight diffraction to measure pole figures. ...
... The crystallographic texture of Ostrea edulis has a different appearance from that of the calcite phase of Mytilus edulis, and is not sharp. It has a maximum value of 2.46 mrd for the (0006) pole figure and 2.38 mrd for the (10)(11)(12)(13)(14) figure, but the shape of the maxima is not similar to the shape of the shell. In the next section, we discuss the differences between the global crystallographic texture for the bivalve molluscs and local textures reported by other researchers. ...
Recently, several studies have focused on the crystallographic texture of bivalve mollusc shells. Unfortunately, these investigations have been limited to the local level. We demonstrate the similarities and differences between the texture measured over the whole shell and that measured over a small part of a shell. An analysis of the global crystallographic texture of bivalve mollusc shells of different genera was carried out using time-of-flight neutron diffraction. The reason for this analysis was to determine whether the crystallographic texture character was similar within the class Bivalvia. It was observed that the shells of mollusc species of the genus Mytilus consist of two phases, calcite and aragonite. Ostrea edulis shells consist of almost pure calcite, whereas Mya arenaria shells consist of almost pure aragonite. It was concluded that the character of the global textures of the different phases in the same shells is different. The advantages of characterisation of the global crystallographic texture are also discussed.
... Other microstructures display a higher degree of ordering, with all axes co-oriented. This is called a sheet texture and is found in bivalve and Nautilus nacre (Hedegaard and Wenk, 1998;Chateigner et al., 2000), the crossed lamellar layers of all extant molluscan classes (Hedegaard and Wenk, 1998;Chateigner et al., 2000;Almagro et al., 2016), the foliated aragonite of monoplacophorans (Checa et al., 2009b,c), the foliated calcite of bivalves , and the fibrous calcite of Mytilidae (Checa et al., 2014a). A rare case is that in which there are two maxima for the c-axis, as in many instances of crossed-lamellar microstructures (Almagro et al., 2016). ...
... Other microstructures display a higher degree of ordering, with all axes co-oriented. This is called a sheet texture and is found in bivalve and Nautilus nacre (Hedegaard and Wenk, 1998;Chateigner et al., 2000), the crossed lamellar layers of all extant molluscan classes (Hedegaard and Wenk, 1998;Chateigner et al., 2000;Almagro et al., 2016), the foliated aragonite of monoplacophorans (Checa et al., 2009b,c), the foliated calcite of bivalves , and the fibrous calcite of Mytilidae (Checa et al., 2014a). A rare case is that in which there are two maxima for the c-axis, as in many instances of crossed-lamellar microstructures (Almagro et al., 2016). ...
Molluscs are grand masters in the fabrication of shells, because these are composed of the largest variety of microstructures found among invertebrates. Molluscan microstructures are highly ordered aggregates of either calcite or aragonite crystals with varied morphologies and three-dimensional arrangements. Classically, every aspect of the fabrication of microstructural aggregates is attributed to the action of proteins. There was, however, only direct evidence that the mineral phase, and indirect evidence that nucleation and the crystal shape, are determined by the types of soluble proteins. Some authors imply that crystal competition may also play a role. In addition, the fabrication of intergranular organic matrices typical of some microstructures (nacre, columnar prismatic) cannot have a protein-based explanation. Over the last decade I and collaborators have been applying a holistic view, based on analyzing and interpreting the features of both the organic (mantle, extrapallial space, periostracum, organic matrices) and inorganic (crystallite morphology, arrangement, and crystallography) components of the biomineralization system. By interpreting them on biophysical principles, we have accumulated evidence that, in addition to the activity of proteins, other mechanisms contribute in an essential way to the organization of molluscan microstructures. In particular, we have identified processes such as: (1) crystal nucleation on preformed membranes, (2) nucleation and growth of crystals between and within self-organized membranes, (3) active subcellular processes of contact recognition and deposition. In summary, besides the activity of organic macromolecules, physical (crystal competition, self-organization) and/or biological (direct cellular activity) processes may operate in the fabrication of microstructures. The balance between the physical and biological determinants varies among microstructures, with some being based exclusively on either physical or biological processes, and others having a mixed nature. Other calcifying invertebrates (e.g., corals, cirripeds, serpulids) secrete microstructures that are very similar to inorganic crystal aggregates, and only some brachiopods and, to a lesser extent, bryozoans may have secretory abilities comparable to those of molluscs. Here I provide a new perspective, which may allow microstructures to be understood in terms of evolutionary constraints, to compare the secretional abilities among taxa, and even to evaluate the probability of mimicking microstructures for the production of functional synthetic materials.
... This 3/3/1 pattern is the only one found in vetigastropods and has also been reported from the nacres of bivalves and Nautilus. 25,26,42 (∞/∞/1) Pattern. The multiple a-and b-axis orientations are randomly oriented around a common c-axis orientation typical of a fiber texture. ...
... This texture is also found in gastropod nacre. 25,26 a/b/2 Textural Patterns. In all of these patterns, as confirmed by the EBSD analyses, each of the two sets of 1st OL (characterized by evenly dipping 3rd OL) provides a single 001 maximum ( Figure 5). ...
Crossed-lamellar microstructures are the most common shell-forming biomaterials in mollusks. Because of their complex hierarchical 3D arrangement and small crystallite size, previous crystallographic studies are scarce and have centered on particular species with no comprehensive analysis available. To evaluate the crystallographic diversity of the crossed-lamellar microstructures, we have studied a large set of bivalve and gastropod species with crossed-lamellar layers using X-ray diffraction and electron backscatter diffraction. From the number, distribution, and relationships of maxima, we have classified pole figures into nine different recurring crystallographic patterns. According to their crystallographic equivalences, these patterns can be grouped into five groups. A first division is established according to whether there is one or two main orientations for the c-axis of aragonite. In the latter case, each orientation corresponds to one of the two sets of alternating first-order lamellae. The two main orientations of the c-axis diverge by rotation within the plane of the first-order lamellae around either a common a- or b-axis. We also show how some patterns may derive from others. Patterns with two c-axis orientations represent crystal relationships until now completely unknown in biogenic and abiogenic aragonite and are most likely produced by particular proteomic pools.
... In a more familiar setting, this concept of making the basic building blocks smaller is similar to what occurs in the semiconductor industry; by making smaller constituent building blocks, integrated circuits and microprocessors can be made more energy efficient and smaller. This ''bottom-up'' construction scheme is a hallmark found in biological materials as well [30,31]. Many of the aforementioned biological materials are built by cellular components whose sizes range from 1 to 100 μm. ...
... Individual tablets are connected by mineral bridges that are the continuation of aragonite growth in the c-axis [92]. At the micrometer scale, nacre can be differentiated into two groups: columnar nacre (for gastropods) or sheet nacre (for bivalves), depending on the stacking order of the aragonite tablets [25,26,30,31]. In columnar nacre, the tablets are stacked such that the inter-tablet edges form tessellated regions that are perpendicular to the lamellae. ...
Biological materials are complex organic–inorganic hybrid materials having characteristic superior functional properties. Most spectacular is the ability for these materials to undergo the processes of growth, development, and regeneration directed by an external stimulus. And in many of these materials, a diversity of structural organizations from the nanometer to the millimeter length scales can be found to create a hierarchically nanostructured bulk material. Complexity is an understatement to describe the structure and function of these biological materials. We attempt to fully understand the superior performances of these biological materials here by drawing attention to the assembly and construction schemes of these nanostructured materials found in nature.
... There are secondary crystals which are much larger in size and distributed haphazardly. At places these crystallites show stacking like 'brick wall' pattern, deposited mostly over inner surface of the shell and recognized as sheet nacre (Hedegaard and Wenk, 1998;Chateigner et al. 2000). In contrast to foliated microstructure, the aragonite nacreous sheets are parallel to the depositional shell surface and the optic-axes are perpendicular to the lamellae or sheets (MacClintock, 1967). ...
... As it has been seen in case of the homogeneous microstructure, which is quite common in these oysters. In many cases simple prismatic microstructures observed in the thin section appears as homogeneous in SEM (Hedegaard and Wenk, 1998). The perceptible break down of distinct crystalline morphology to form homogeneous structures can arise from different types of structures producing a fine grained irregular granular structure. ...
The micro-morphological shell characters (both in optical microscope and SEM) have been used to discriminate in between oyster’s sub-families Pycnodonteinae Stenzel 1959, Exogyrinae Vyalov 1936, Ostreinae Refinesque 1815 and Lophinae Vyalov 1936. These sub-families are represented by six constituent genera Phygraea (Phygarea) vesicularis (Lamarck 1806), Hyotissa semiplana (Sowerby1813), Curvostrea rouvellei (Coquand 1862), Ceratostreon pliciferum (Dujardin 1837), Agerostrea ungulata (Schlotheim 1813) and Rastellum (Arctostrea) pectinatum (Lamarck 1810) in the late Cretaceous (Maastrichtian) sediments of the Ariyalur area of Tamil Nadu, south India. The optical microscopic observations and SEM studies of the shells of these six genera clearly indicate that all the four sub-families consist of distinctive set of shell-microstructures. Sub-family Pycnodonteinae is characterized by predominance of vesicular, exogyrinae by prismatic, Ostreinae by cross foliated and Lophinae by foliated shell microstructures. Besides their characteristic shell microstructures, some additional microstructures are also visible in the shells of some of the genera of these four sub-families.
... The second category is a columnar, nacreous layer. This category is found in some gastropods and cephalopods, such as Haliotis cracherodi, Tectus pyramis and Perotrochus quoyanus (Hedegaard and Wenk 1998). This microstructure category consists of flattened aragonite blades or laths, common to Bivalvia, including Pterioda, Pectinacea, Anomiacea and Ostreacea (Waller 1972(Waller , 1978. ...
... Nacre is particularly strong, but because it is so often absent from the nacreous layer, it appears that its energetic expense sometimes outweighs its structural advantages. Hedegaard and Wenk (1998) . Propagation of juvenile top shell for reseeding depleted natural stocks offers an opportunity to re-establish the Trochus fishery at a higher level in Thailand (Chunhabundit and Thapanand 1993a, b). ...
Maculated top shells grew rapidly when co-cultured in tanks with fish and fed on leftover fish feed and fish wastes. During rapid growth on this high protein diet, top shells deposited a red band on their outer shell surface. Top shells reared in tanks without fish and fed only algal diets decreased in size. With the nutritionally deficient diet, top shells deposited a purple band on their outer shell surface. Shell microstructures were observed and described for these two conditions using a scanning electron micro- scope, which revealed substantial differences between shell structures under well-fed and nutritionally deficient conditions.
... Quantitative texture analysis is used to characterise the macroscopic organisation of layer crystals in mollusc shells. High degree of order (or texture strength) have been reported [52,26], which vary between taxon with qualitatively identical textures in close species [27], and in a single specimen with the location in the shell, either between different layers [35,53] or in the same layer [24]. As a global scheme, organic macromolecules that form matrices of the shells are controlling the inorganic crystal orientations [22] and also crystal shapes themselves [21], in such a way that these two informations can be seen as non-redundant. ...
... From previous analysis we know there is a non-trivial relationship between the crystallographic textures (orientation distribution of crystals) and shell ultrastructures of mollusc shells [55,53,52,27,35]. Textures differ in shell structures with similar morphological patterns between distantly related molluscs, and may vary between layers within an individual. ...
... A second problem exists in distinguishing Paleozoic tryblidians from patellogastropodsboth usually preserved as internal molds (steinkerns)-because even extant forms have been repeatedly confused by earlier authors (see Table 5.1) and indeed are very similar in shape and the general pattern of shell muscle insertion areas. Nacreous shell structure (e.g., MacClintock 1967, Erben et al. 1968Hedegaard and Wenk 1998) and a broad, capshaped protoconch (e.g., Wingstrand 1985) are hallmarks of tryblidians but are usually not found in fossils because of poor preservation. The only other clear difference between tryblidian and patellogastropod fossils is found in the (granular) insertion area of the paired radular retractor (Tryblidia) versus the (homogeneous) one of the paired head retractor (Patellogastropoda), both of which show a similar position (Figure 5.2). ...
... 2a) or columnar nacre (CN, Fig. 2b) according to the stacking mode of platelets (Taylor et al., 1969;Wang et al., 2001). The platelets in CN present a rather uniform size with coinciding centers (nucleation core), and the overlap region covers around 1/3 of the area of a platelet (Fig. 2b), while they are stacked in a "brick wall" pattern, and no distinction can be found between the core and overlap areas in SN (Hedegaard, 1997;Hedegaard and Wenk, 1998;Chateigner et al., 2000). Shells normally present SN in class Bivalvia and CN in class Gastropoda (Chateigner et al., 2000;Rousseau et al., 2005a, b;Heinemann et al., 2011;Yourdkhani et al., 2011). ...
Nacre, known as mother of pearl, has evolved unique combination of mechanical properties to fulfill its specific function through the hierarchical structure. Such a complex structural hierarchy of nacre spans four or five length scales, arising from the assembly of different sized building blocks during its natural growth. Nacre`s special self-assembly structure arouses several toughening mechanisms to defeat the conflict of strength versus toughness, thus boasting remarkable mechanical properties. The major influencing factors on the mechanical properties of nacre including loading direction, loading rate, hydrated state, dimension of specimens and aragonite platelets, etc., are summarized.
... A reversal correlation takes place between the ratio of calcite in the shell and the mean temperature of the environment inhabited by the bivalve 3 . Paleontology has fundamentally disseminated on scanning electron microscopy (SEM) for a specific depiction of shell microstructures [4][5][6][7] . The prime objective of the present study is to assess the morphological, chemical, mineralogical and microstructural characteristics of the Meretrix meretrix shells occurred on the Toothukudi coast of Tamil Nadu, India. ...
Bivalve shells are an affluent source of calcium content and significant for lime-based industries development. Indian coastlines are rich in bivalve shells occurrences. In this study, Meretrix meretrix (Bivalvia, Veneridae) shells of Thoothukudi coast of Tamil Nadu are taken to study the biochemistry, biomineralization and microstructure characteristics of the shell. After the morphological investigation, the shells were made into fine powder for mineralogical and chemical analysis. XRF and XRD instruments were used for chemical and mineralogical measurements. Shell microstructure examination carried out using SEM. The XRF results reveal a high percentage of CaO content in the shell along with Fe, Sr and Mo. The XRD exhibits 12 peaks; all the peaks report aragonite minerals. The microstructures are examined in the shell portions of growth lines and umbo. The umbo part exhibits irregular homogeneous microstructures, whereas the growth lines exhibit granular homogeneous structure and prismatic structures. The umbo part consists of pore spaces which signify the growth of the shell is incomplete due to less availability of the extrapallial fluid (EPF). In the growth line part, two parallel sets of linear depression mark are present, which signifies that there is no sufficient nacre to spread uniformly throughout the shell. This study indicates that the study area Meretrix meretrix shells are formed by biogenic aragonite to a greater concentration, which has been proven with XRD and SEM analysis.
... However, M. truncata actually shared more proteins with C. gigas and P. maximus than M. edulis. This result cannot be explained purely by the differences in the crystal structure of the shells of the different species (Hedegaard and Wenk 1998;Chateigner et al. 2000), as the C. gigas shell is completely calcite, whereas that of M. truncata is completely aragonite. M. edulis, which is a mix of aragonite and calcite, would be expected to share significant protein homologies with both. ...
In this study, the SMPs from four commercially important and divergent bivalve species crassostrea gigas (pacific oyster), Mya truncata (soft shell clam), Mytilus edulis (blue mussel) and Pecten maximus (king scallop) were extracted and analysed using standardized extraction protocol and proteomic pipeline. This enables us to identify critical elements of basic biomineralization tool kit for calcification process irrespective of their shell morphology, mineralogy and microstructure. In addition, it enables the identification of SMPs that are specific to calcite and aragonite mineralogies. The signifiant numbers of SMPs found species-specific were hypothesized as adaptation to their modus vivendi. In fact, the latter proteins possess immunity-related functions and fit into specific pathway, phenoloxidase, suggesting their role in defense against pathogen. The comparative study of shell proteome of mussels living in full marine condition, North Sea and the Iow saline Baltic Sea showed the modulation of the SMPs that constitute the basic biomineralization tool kit. Higher modulation of chitin related proteins and non-modulated protein such as carbonic anhydrase, EGF and fibronectin domain containing proteins points out the impaired scaffold and mineral nucleation process in Baltic mussel. The modulation of immunity related proteins denote the influence of biotic components. These investigations show the functional diversity of SMPs and their roles beyond shell formation in the bivalvesand put forth the idea that shell is dynamic, endowed with both biochemical and mechanical protection.
... Khidr Fatma et al., (2011) found that Thyophyline decreased total protein after 4 days of treatment for Monacha obstructa. Hedegaard and wenk (1998) mentioned that mollusca shell is polycrystalline composites of calcium carbonate, Protein and glycoprotein. Also Karl and Saleuddin (1983) mentioned that the formation of shell can be described in terms of two major phases: (1) cellular processes of ion transport, protein synthesis, and secretion and (2) a series of physicochemical processes in which crystals of CaCO 3 are nucleated, oriented, and grow in intimate association with a secreted organic matrix. ...
Effect of different compounds against some principle calcium precipitation parameters in shell was studied on two terrestrial snails, Eobania vermiculata and Monacha obstructa. The tested compounds were Newmyl (the recommended compound), Lambada, Actra as synthetic compound, Tracer (bioinsecticide) and Tannic acid (natural product). Animals of each species were treated with LC 50 of each compound using contact technique. The calcium precipitation parameters (Alkaline phosphatase (ALP), Acid phosphatase (ACP), Total protein (TP), Total lipid (TL) and cholesterol) were measured after one, three and seven days post treatment. Results showed that all tested compounds caused vacillated effects for the two snail species. Tannic acid and tracer were the most effective compounds on the all parameters in both species. While the recommended compound (newmyl) came in the last rank in the most of parameters. E. vermiculata was more susceptible to tannic acid than M. obstructa for ALP, ACP enzymes, total protein and cholesterol, while both species had the same response to total lipid. The fluctuation effects of tested biochemical parameters may be due to damage of cells under the impact of treatment with compounds.
... Khidr Fatma et al., (2011) found that Thyophyline decreased total protein after 4 days of treatment for Monacha obstructa. Hedegaard and wenk (1998) mentioned that mollusca shell is polycrystalline composites of calcium carbonate, Protein and glycoprotein. Also Karl and Saleuddin (1983) mentioned that the formation of shell can be described in terms of two major phases: (1) cellular processes of ion transport, protein synthesis, and secretion and (2) a series of physicochemical processes in which crystals of CaCO 3 are nucleated, oriented, and grow in intimate association with a secreted organic matrix. ...
... Their role in metal detoxification has also been tested by several authors (Marigomez et al., 1995). Hedegaard and Wenk (1998) mentioned that mollusca shells are polycrystalline composites of calcium carbonate, proteins and glycoproteins, shielding the animals from the environment. Their strength and toughness are crucial survival of the individuals. ...
ABSTRACT
The Molluscicidal activity of 5 pesticides (methomyl, L- cyhalothrin, thiamethoxam, abamectin and spinosad) and two acids (acetylsalicylic acid and tannic acid) and their combinations was studied against two land snail species, Eobania vermiculata and Monacha obstructa under laboratory and field conditions. Results showed that abamectin was the most toxic one when used as a bait or contact against both species. Also, the contact technique was more effective than the bait method. The combination of acetylsalicylic acid with methomyl as a bait gave high potency effect (100% co-toxicity) factor against the two snail species. While antagonism effect was recorded when used as contact for M. obstructa. Under field conditions, the combination of acetylsalicylic acid with methomyl was the most effective one against both snail species. The effect of tested compounds on the biochemical parameters (alkaline and acid phosphate, total protein, lipid and cholesterol) was determined. Results showed that the combination of acetylsalicylic acid and methomyl exhibited the highest effect on all biochemical parameter as bait or contact. The LC50 of acetylsalicylic acid caused desiccation and adhesive for snail body of both species while tannic acid caused intense damage in the shell and cannibalism effect for E. vermiculata, while it caused dryness and change in the body color of M. obstructa. The histopathological effects of LC50 of acetylsalicylic acid on the tissues of mucous gland was studied in both snail species. It was partial as well as complete disappearance, necrosis and atrophy of mucous glandular tissue for E. vermiculata. While it was focal necrosis specially underneath necroses destructed covering epithelium in association with degeneration in case of M. obstructa.
Key words: Eobania vermiculata- Monacha obstructa- Abamectin- Spinosad- Acetylsalicylic acid- Tannic acid- Joint action.
... Cephalopods produce nacre that is an intermediate of the two (Vendrasco, Checa, & Kouchinsky, 2011). In addition, the tablets in gastropod, bivalve and cephalopod nacre each display different crystallographic axes (Hedegaard & Wenk, 1998). Based on these differences it has been hypothesized that nacre may have originated several times independently (Jackson et al., 2010;Marie et al., 2009;Vendrasco et al., 2011), therefore caution needs to be exercised when making generalizations relating to superficially similar shell layer microstructures. ...
Molluscan shells are externally fabricated by specialized epithelial cells on the dorsal mantle. Although a conserved set of regulatory genes appears to underlie specification of mantle progenitor cells, the genes that contribute to the formation of the mature shell are incredibly diverse. Recent comparative analyses of mantle transcriptomes and shell proteomes of gastropods and bivalves are consistent with shell diversity being underpinned by a rapidly evolving mantle secretome (suite of genes expressed in the mantle that encode secreted proteins) that is the product of (a) high rates of gene co‐option into and loss from the mantle gene regulatory network, and (b) the rapid evolution of coding sequences, particular those encoding repetitive low complexity domains. Outside a few conserved genes, such as carbonic anhydrase, a so‐called “biomineralization toolkit” has yet to be discovered. Despite this, a common suite of protein domains, which are often associated with the extracellular matrix and immunity, appear to have been independently and often uniquely co‐opted into the mantle secretomes of different species. The evolvability of the mantle secretome provides a molecular explanation for the evolution and diversity of molluscan shells. These genomic processes are likely to underlie the evolution of other animal biominerals, including coral and echinoderm skeletons.
This article is categorized under: Comparative Development and Evolution > Regulation of Organ Diversity
Comparative Development and Evolution > Evolutionary Novelties
... However, M. truncata actually shared more proteins with C. gigas and P. maximus than M. edulis. This result cannot be explained purely by the differences in the crystal structure of the shells of the different species (Hedegaard and Wenk 1998;Chateigner et al. 2000), as the C. gigas shell is completely calcite, whereas that of M. truncata is completely aragonite. M. edulis, which is a mix of aragonite and calcite, would be expected to share significant protein homologies with both. ...
Bivalves have evolved a range of complex shell forming mechanisms that are reflected by their incredible diversity in shell mineralogy and microstructures. A suite of proteins exported to the shell matrix space plays a significant role in controlling these features, in addition to underpinning some of the physical properties of the shell itself. Although, there is a general consensus that a minimum basic protein tool kit is required for shell construction, to date, this remains undefined. In this study the shell matrix proteins (SMPs) of four highly divergent bivalves (The Pacific oyster, Crassostrea gigas; the blue mussel, Mytilus edulis; the clam, Mya truncata and the king scallop, Pecten maximus) were analyzed in an identical fashion using proteomics pipeline. This enabled us to identify the critical elements of a " basic tool kit " for calcification processes, which were conserved across the taxa irrespective of the shell morphology and arrangement of the crystal surfaces. In addition, protein domains controlling the crystal layers specific to aragonite and calcite were also identified. Intriguingly, a significant number of the identified SMPs contained domains related to immune functions. These were often are unique to each species implying their involvement not only in immunity, but also environmental adaptation. This suggests that the SMPs are selectively exported in a complex mix to endow the shell with both mechanical protection and biochemical defense.
... It consists of consecutive layers of small CaCO 3 crystals deposited parallel to the shell plane embedded in an organic matrix of chitinlike mucopolysaccharide and protein (Machado et al., 1994) (Fig. 3). Microstructure and texture patterns of CaCO 3 crystals differ among major molluscan classes and interspecifically within groups (Hedegaard and Wenk, 1998). Continual secretion of the nacreous layer thick-ens and strengthens the shell, thus accounting for most of its mass. ...
... It consists of consecutive layers of small CaCO 3 crystals deposited parallel to the shell plane embedded in an organic matrix of chitinlike mucopolysaccharide and protein (Machado et al., 1994) (Fig. 3). Microstructure and texture patterns of CaCO 3 crystals differ among major molluscan classes and interspecifically within groups (Hedegaard and Wenk, 1998). Continual secretion of the nacreous layer thick-ens and strengthens the shell, thus accounting for most of its mass. ...
North American (NA) freshwater bivalve molluscs (class Bivalvia) fall in the subclasses Paleoheterodonta (Superfamily Unionoidea) and Heterodonta (Superfamilies Corbiculoidea and Dreissenoidea). They have enlarged gills with elongated, ciliated filaments for suspension feeding on plankton, algae, bacteria, and microdetritus. The mantle tissue underlying and secreting the shell forms a pair of lateral, dorsally connected lobes. Mantle and shell are both single entities. During development, the right and left mantle lobes extend ventrally from the dorsal visceral mass to enfold the body. Each lobe secrets a calcareous shell valve which remains connected by a mid-dorsal isthmus. Like all molluscs, the shell valves consist of outer proteinaceous and inner crystalline calcium carbonate elements. The lateral mantle lobes secrete shell material marked by a high proportion of crystalline calcium carbonate making them thick, strong and inflexible, while the mantle isthmus secretes primarily protein, forming a dorsal elastic hinge ligament uniting the calcareous valves. The hinge ligament is external in all freshwater bivalves. Its elasticity opens the valves while the anterior and posterior shell adductor muscles run between the valves and close them in opposition to the hinge ligament which opens them on adductor muscle relaxation. The key presented in this chapter, as well as many of the major keys to freshwater bivalves, relies on the integrated use of important anatomical structures and shell characters to identify unionoidean bivalves. This key is artificial, and it is divided into four sections corresponding to geographical provinces to facilitate identification.
... In the shells of many bivalves, including pearl oysters, there are two conspicuous layers: the prismatic layer, covering the outer surface of the shell, and the nacreous layer facing the soft body. Both layers are primarily composed of a regular array of calcium carbonate crystals (Hedegaard and Wenk, 1998), but the prismatic layer is made of calcite whereas the nacreous layer is made of aragonite (Wilt et al., 2003). These two layers appear to be constructed by processes involving both a biological apparatus and the selforganizing properties of crystals. ...
In molluscs, shell matrix proteins are associated with biomineralization, a biologically controlled process that involves nucleation and growth of calcium carbonate crystals. Identification and characterization of shell matrix proteins are important for better understanding of the adaptive radiation of a large variety of molluscs. We searched the draft genome sequence of the pearl oyster Pinctada fucata and annotated 30 different kinds of shell matrix proteins. Of these, we could identified Perlucin, ependymin-related protein and SPARC as common genes shared by bivalves and gastropods; however, most gastropod shell matrix proteins were not found in the P. fucata genome. Glycinerich proteins were conserved in the genus Pinctada. Another important finding with regard to these annotated genes was that numerous shell matrix proteins are encoded by more than one gene; e.g., three ACCBP-like proteins, three CaLPs, five chitin synthase-like proteins, two N16 proteins (pearlins), 10 N19 proteins, two nacreins, four Pifs, nine shematrins, two prismalin-14 proteins, and 21 tyrosinases. This diversity of shell matrix proteins may be implicated in the morphological diversity of mollusc shells. The annotated genes reported here can be searched in P. fucata gene models version 1.1 and genome assembly version 1.0 ( http://marinegenomics.oist.jp/pinctada_fucata ). These genes should provide a useful resource for studies of the genetic basis of biomineralization and evaluation of the role of shell matrix proteins as an evolutionary toolkit among the molluscs.
... This offers an advantage to the juvenile, since the large foot is the main organ in the anterior region and needs to be protected against predators and physical agents so that it can fulfill the important function of seeking food. As in other bivalve shells, from the 30-day-old juvenile through to the adult, the shell microstructure of H. (L.) myersiana consists of three layers, namely, periostracum, prismatic layer and nacreous layer (Hedegaard and Wenk, 1998). The periostracum layer of H. (L.) myersiana is thin and this may offer little resistance to aggressive agents and organisms in the environment (Bottjer and Carter, 1980;Kovitvadhi et al., 2001a). ...
The morphological development of the freshwater mussel, Hyriopsis (Limnoscapha) myersiana (Lea, 1856), was observed using light and scanning electron microscopes, from the newly transformed (0 days old) juvenile to the onset of the adult stage (360 days old). As in the glochidium, the early juvenile has a semi-oval and equivalve shell with an equilateral valve. After day 1 the shell develops a larger anterior than posterior region until day 40, after which the posterior region grows larger than the anterior region. The form of the juvenile at 260-day-old resembles that of a fully grown adult. The shell microstructure of 0–20-day-old juveniles shows two differentiated layers, the periostracum and the prismatic layer. By day 30 the prismatic layer lies under a clear columnar structure that has formed a third layer, the nacreous layer. The mantle develops incurrent and excurrent siphons when juveniles are 60 days old. The development of juvenile gills initiates from a pair of gill bars at 0 days old, and formation of the inner demibranch starts from 10 days old and the outer demibranch from 90 days old. From this stage, numerous cilia form the latero-frontal cirri of the inner demibranchs. Additionally, longitudinal and transversal interfilamentous junctions of the inner and outer demibranchs begin to develop when juveniles are 200 and 240 days old and are complete at 230 and 260 days of age, respectively. Interlamellar septa join the inner surface of descending and ascending gill filaments to form water chambers when juveniles are 250 and 280 days old, respectively, and the development of inner and outer demibranchs is complete.
... Columnar nacre has tablets of a rather uniform size with coinciding centers that determine the nucleation site of the overlying tablet, while in sheet nacre deposition takes place over most of the inner surface of the shell, and the tablets are stacked in a ''brick wall'' pattern, spanning the interface between the underlying tablets. [81][82][83] Generally, columnar nacre is found in gastropods, whereas sheet nacre occurs more in bivalves. 45 In columnar nacre, viewed from the top, the polygonal tablets from neighboring layers overlap in such a manner that the inter-tablet boundaries form tessellated bands perpendicular to the lamellae boundaries, shown in Fig. 4c-e. ...
Nacre (known as mother of pearl) is the iridescent inner shell layer of some mollusks. Nacre is composed of 95 wt% aragonite (a crystallographic form of CaCO3) and 5 wt% organic materials (proteins and polysaccharides). It is well known that it exhibits high fracture toughness, much greater than that of monolithic aragonite, because of its ingenious structure. It also exhibits energy absorption properties. It has a complex hierarchical microarchitecture that spans multiple length scales from the nanoscale to the macroscale. It includes columnar architectures and sheet tiles, mineral bridges, polygonal nanograins, nanoasperities, plastic microbuckling, crack deflection, and interlocking bricks, which exhibit a remarkable combination of stiffness, low weight and strength. Nacre's special self-assembly characteristics have attracted interest from materials scientists for the development of laminated composite materials, molecular scale self-assembly and biomineralization. This paper reviews the characteristics of hierarchical structure and the mechanical properties of nacre that provide the desired properties, and the latest developments and biomimetic applications.
... Two types of QTA have been applied to the Mollusca in the literature, which differ in the radiation used, thereby probing different material scales. While X-ray diffraction was formerly used (Chateigner et al. 1996, 2000, Hedegaard and Wenk 1998, Electron Backscatter Diffraction (EBSD) has more recently provided a way for local characterization of texture variation in molluscs (Checa et al. 2005, Rousseau et al. 2005. Dealing with X-ray analysis using whole X-ray diffraction profi les accounts for all the crystallites, even the smallest ones. ...
X-ray Quantitative Texture Analysis (QTA) results are examined for the outer aragonitic shell layers of Helix aspersa aspersa (Müller, 1774) to probe the relevance of the approach to non-fl at surfaces. Two sets of H. aspersa aspersa were studied, for a total of 29 samples. Quantitative texture analysis showed that although the nature of the texture present was roughly constant, the textural strength varied signifi cantly among specimens because of biologically inherited surface irregularities. A statistical analysis showed that textural strength exhibited larger standard deviations for snails selected for greater shell weight than for control snails. The H. aspersa aspersa aragonite texture is the same as observed in previous studies, with <110> shell growth directions. This texture causes elastic behavior of the mineral part of the shell, which accommodates moderate shear and compression. We furthermore determine that the colored bands at the shell surface were aligned with the <020> crystal directions.
... The orientation of the crystallographic axes in the aragonite tablets of the molluscan nacre has been studied by X-ray diffraction (e.g. Wada 1961; Wise 1970; Hedegaard and Wenk 1998; Chateigner et al. 2000; Hou and Feng 2003; Fryda et al. 2007). In our preparations of the shell wall and septa, the vertical crystalline lamellae in the nacreous tablets are parallel to the longitudinal axis of the tablet. ...
The nacreous layer in Gibbula, Calliostoma, Trochus and Haliotis is described on the basis of scanning electron microscopic studies. The central part of each nacreous tablet contains a significant amount of calcified organic matrix which is insoluble in a chromium sulphate and a 25% glutaraldehyde solution. In most cases, the tablet is subdivided by radial vertical organic membranes into a varying number (2 to 50) of crystalline sectors. These sectors represent polysynthetically twinned crystal individuals which form cyclic or interpenetrant twins. The nacreous tablets in gastropods are compared with those in bivalves, and with the non-biogenic aragonite. The mechanical properties of the nacre, and the effects of the interlamellar conchiolin membranes upon the nucleation of the tablets, are discussed.
... The shell structure of the Galathea specimens and fossil monoplacophorans was studied by Schmidt (1959), Erben et al. (1968), Meenakshi et al. (1970), McLean (1979, and Hedegaard and Wenk (1998). In Recent species, the outer surface of the shell is covered by a thin periostracum, and under the periostracum is an outer prismatic shell layer and an inner nacreous layer-the traditional primitive shell structure configuration. ...
The story of the discovery and study of the Monoplacophora (or Tryblidia) and how they have contributed to our understanding
of the evolution of the Mollusca highlights the importance of integrating data from the fossil record with the study of living
forms. Monoplacophora were common in the early Paleozoic and were thought to have become extinct during the Devonian Period,
approximately 375Mya. In the mid 1950s, they were recovered from abyssal depths off of Costa Rica and were immediately heralded
as a “living fossil.” The living specimens confirmed that some of the organs (kidneys, heart, and gills) were repeated serially,
just like the shell muscles that had been observed in fossil specimens. This supported the hypothesis that they were closely
related to other segmented organisms such as annelids and arthropods. Today, there are 29 described living species and a growing
body of work examining their anatomy, phylogeny, and ecology. Additional fossil specimens have also been discovered, and what
was once thought to be a possible missing link between annelid worms and mollusks now appears to be a highly specialized branch
of the molluscan tree that tells us little about the ancestral mollusk condition. However, some assumptions and generalizations
from those early days still remain—such as the abyssal nature of the living species. A large part of the evolutionary history
of the lineage remains to be discovered and will likely prove more complicated and interesting than afforded by the living
fossil designation.
... First, the interlamellar matrix is assumed to be predominantly constituted of b-chitin fibrils that are aligned with the a-axis of the growing aragonitic tablets [20], suggesting that they can be, directly or indirectly, implicated in the control of the crystal orientation [21]. On the other hand, the b-and c-axes of the nacre tablets are oriented in parallel to the growing front in bivalves, whereas this is not the case in gastropods [22]. These data suggest that chitin is therefore either not fulfilling this role in nacre formation or that not all nacres are constructed in the same way, as recently suggested by Jackson et al. [23]. ...
Unlabelled:
In molluscs, and more generally in metazoan organisms, the production of a calcified skeleton is a complex molecular process that is regulated by the secretion of an extracellular organic matrix. This matrix constitutes a cohesive and functional macromolecular assemblage, containing mainly proteins, glycoproteins and polysaccharides that, together, control the biomineral formation. These macromolecules interact with the extruded precursor mineral ions, mainly calcium and bicarbonate, to form complex organo-mineral composites of well-defined microstructures. For several reasons related to its remarkable mechanical properties and to its high value in jewelry, nacre is by far the most studied molluscan shell microstructure and constitutes a key model in biomineralization research. To understand the molecular mechanism that controls the formation of the shell nacreous layer, we have investigated the biochemistry of Nautilin-63, one of the main nacre matrix proteins of the cephalopod Nautilus macromphalus. After purification of Nautilin-63 by preparative electrophoresis, we demonstrate that this soluble protein is glycine-aspartate-rich, that it is highly glycosylated, that its sugar moieties are acidic, and that it is able to bind chitin in vitro. Interestingly, Nautilin-63 strongly interacts with the morphology of CaCO(3) crystals precipitated in vitro but, unexpectedly, it exhibits an extremely weak ability to inhibit in vitro the precipitation of CaCO(3) . The partial resolution of its amino acid sequence by de novo sequencing of its tryptic peptides indicates that Nautilin-63 exhibits short collagenous-like domains. Owing to specific polyclonal antibodies raised against the purified protein, Nautilin-63 was immunolocalized mainly in the intertabular nacre matrix. In conclusion, Nautilin-63 exhibits 'hybrid' biochemical properties that are found both in the soluble and insoluble proteins, rendering it difficult to classify according to the standard view on nacre proteins.
Database:
The protein sequences of N63 appear on the UniProt Knowledgebase under accession number P86702.
... To address this question one may examine: (i) the perfect co-orientation in mesocrystals 6 which is not always observed in biominerals, when analyzed with high-resolution methods; 16,37,[52][53][54] (ii) the much higher concentration of organics in carbonate mesocrystals 7 than in biominerals; 55,56 (iii) the presence of facets in mesocrystals, 6 which is conspicuously absent in biominerals; (iv) finally, the space-filling reported here, which is far greater for biominerals than for mesocrystals. The surface areas are in fact in the 1-2 m 2 /g range for the biominerals examined here, and >250 m 2 /g for mesocrystals. ...
Sea urchin biominerals have been shown to form from aggregating nanoparticles of amorphous calcium carbonate (ACC), which then crystallize into macroscopic single crystals of calcite. Here we measure the surface areas of these biominerals and find them to be comparable to those of space-filling macroscopic geologic calcite crystals. These biominerals differ from synthetic mesocrystals, which are invariably porous. We propose that space-filling ACC is the structural precursor for echinoderm biominerals.
Purpose
In the present work, a nacre-like composite-material, consisting of tablets and polyurea tablet/tablet interfaces, B4C is modeled. This composite material is being considered in the construction of the so-called backing-plate, a layer within a multi-functional/multi-layer armor system.
Design/methodology/approach
Considering the basic functions of the backing-plate (i.e. to provide structural support for the ceramic strike-face and to stop a high-velocity projectile and the accompanying fragments) in such an armor system, the composite-material architecture is optimized with respect to simultaneously achieving high flexural stiffness and high ballistic-penetration resistance. Flexural stiffness and penetration resistance, for a given architecture of the nacre-like composite-material, are assessed using a series of transient non-linear dynamics finite element analyses. The suitability of the optimized composite material for use in backing-plate applications is then evaluated by comparing its performance against that of the rolled homogeneous armor (RHA), a common choice for the backing-plate material.
Findings
The results obtained established: (a) a tradeoff between the requirements for a high flexural stiffness and a high ballistic-penetration resistance in the nacre-like composite material; and (b) overall superiority of the subject composite material over the RHA when used in the construction of the backing-plate within multi-functional/multi-layer armor systems.
Originality/value
This study extends our previous research on nacre-mimetic armor to optimize the architecture of the armor with respect to its flexural stiffness and ballistic-penetration resistance, so that these properties could be increased over the levels attained in the current choice (RHA) for the backing-layer of multi-functional/multi-layer armor.
The crossed-lamellar structure is known to exhibit a fantastic microarchitecture and excellent fracture resistance. Despite a similar morphology, this structure belongs to a family of homeomorphic microstructures with complex and varied crystallographies. In the present study, the crystallographies of different parts in Cymbiola nobilis shell were studied. The width of the first building blocks becomes increasingly thicker from the top to bottom of inner and middle layers. All the crystallites tend to align their c-axes towards the shell surface, and two twinned crystals share the c-axis at the top of inner and middle layers, while at the bottom the 001 pole figure shows two orientation components with c-axes inclined, and four preferential b-axis orientations distributed into two pairs. Texture analysis provides important information about the nature of shell growth, and suggests that the shape of the building blocks may be controlled by the crystallographic arrangement during the aragonite deposition.
Purpose
Nacre is a biological material constituting the innermost layer of the shells of gastropods and bivalves. It consists of polygonal tablets of aragonite, tessellated to form individual layers and having the adjacent layers as well as the tablets within a layer bonded by a biopolymer. Due to its highly complex hierarchical microstructure, nacre possesses an outstanding combination of mechanical properties, the properties which are far superior to the ones that are predicted using techniques such as the rule of mixtures. Given these properties, a composite armor the structure of which mimics that of nacre may have improved performance over a monolithic armor having a similar composition and an identical areal density. The paper aims to discuss these issues.
Design/methodology/approach
In the present work, an attempt is made to model a nacre-like composite armor consisting of B4C tablets and polyurea tablet/tablet interfaces. The armor is next tested with respect to impact by a solid right circular cylindrical (SRCC) rigid projectile, using a transient non-linear dynamics finite-element analysis. The ballistic-impact response and the penetration resistance of the armor are then compared with that of the B4C monolithic armor having an identical areal density. Furthermore, the effect of various nacre microstructural features (e.g. surface profiling, micron-scale asperities, mineral bridges between the overlapping tablets lying in adjacent layers, and B4C nano-crystallinity) on the ballistic-penetration resistance of the composite armor is investigated in order to identify an optimal nacre-like composite armor architecture having the largest penetration resistance.
Findings
The results obtained clearly show that a nacre-like armor possesses a superior penetration resistance relative to its monolithic counterpart, and that the nacre microstructural features considered play a critical role in the armor-penetration resistance.
Originality/value
The present work indicates that for a given choice of armor material, penetration resistance may be improved by choosing a structure resembling that of nacre.
A nacre-like composite armor consisting of B4C tablets and polyurea matrix is modeled, and its ballistic impact behavior and penetration resistance (under a normal and a 15°-oblique impact by a solid right circular cylindrical projectile) were analyzed using a series of transient, nonlinear dynamic, finite-element analyses. Nacre is a biological material constituting the innermost layer of the shells of gastropods and bivalves. It consists of polygonal tablets of aragonite, tessellated to form individual layers and having the adjacent layers as well as the tablets within a layer bonded by a biopolymer. Due to its highly complex
hierarchical microstructure, nacre possesses an outstanding combination of mechanical properties, the properties which are far superior to the ones that are predicted using the homogenization techniques such as the rule of mixtures. The results of the transient nonlinear dynamic analysis pertaining to the ballistic impact response and the penetration resistance of the modeled nacre-like armor are compared with their counterparts for the B4C single-block armor having an identical areal density. Furthermore, the effect of various nacre microstructural features (e.g., surface profiling, micron-scale asperities, mineral bridges between the overlapping tablets lying in adjacent layers) on the ballistic penetration resistance of the nacre-like composite armor is investigated in order to identify an optimal nacre-like composite-armor architecture having the largest penetration resistance. The results obtained clearly show that a nacre-like armor possesses a superior penetration resistance relative to its monolithic counterpart, and that the nacre microstructural features considered play a critical role in the armor penetration resistance.
Nacre is a biological material constituting the innermost layer of the shells of gastropods and bivalves. It consists of polygonal tablets of aragonite, tessellated to form individual layers and having the adjacent layers as well as the tablets within a layer bonded by a biopolymer. Due to its highly complex hierarchical microstructure, nacre possesses an outstanding combination of mechanical properties, the properties which are far superior to the ones that are predicted using the techniques such as the rule of mixture. In the present work, an attempt is made to model a nacre-like composite armor consisting of boron carbide (B4C) tablets and polyurea tablet/tablet interfaces. The armor is next investigated with respect to impact by a solid right-circular-cylindrical rigid projectile, using a transient non-linear dynamics finite element analysis. The ballistic-impact response and the penetration resistance of the armor is then compared with that of the B4C monolithic armor having an identical areal density. Furthermore, the effect of various nacre microstructural features (e.g. surface profiling, micron-scale asperities, mineral bridges between the overlapping tablets lying in adjacent layers, and B4C nano-crystallinity) on the ballistic-penetration resistance of the composite-armor is investigated in order to identify an optimal nacre-like composite-armor architecture having the largest penetration resistance. The results obtained clearly show that a nacre-like armor possesses a superior penetration resistance relative to its monolithic counterpart, and that the nacre microstructural features considered play a critical role in the armor penetration resistance.
In the literature, the growth of inorganic materials below negatively charged monolayers is frequently considered to be a suitable model system for biominer-alization processes. The fact that some monolayers give rise to oriented overgrowth of calcium carbonate crystals has been interpreted in terms of a geometrical and stereochemical complementarity between the arrangement of headgroups in the monolayer and the position of Ca ions in the crystal plane that attaches to the monolayer. Recent investigations into the mechanisms of nacre formation in mollusk shells, as well as comparative studies on suitably adapted model systems, suggest that this commonly held view of a structure-directing organic template matrix represents an oversimplified concept of the complex crystallization process.
Compared to their Recent counterparts, fossil abalone are rare and poorly known. Their taxonomy is problematic, because most of the 35 fossil species have been described from single specimens and shell characteristics of Recent species are extremely plastic. Thus, the use of fossil species in phylogeny is questionable. Abalone first appear in the Upper Cretaceous (Maastrichian) with one species each in California and the Caribbean, are unknown in the Paleocene, and appear again in the late Eocene and Oligocene of New Zealand and Europe. They are regularly found from the late Miocene to the Recent in tropical to temperate regions worldwide. Most records are from intensely studied areas: SW North America, Caribbean, Europe, South Africa, Japan, and Australia. Despite their highest present-day diversity being found in the Indo-Pacific, their scarcity in the fossil record in this region is remarkable. The family may have originated in the central Indo-Pacific, Pacific Rim, or Tethys. An extensive list of all known fossil records including new ones from Europe and western North America is given. Fossil and Recent abalone both apparently lived in the shallow, rocky sublittoral in tropical and temperate climates. No on-shore/off-shore pattern is detected.
Microstructural details are revealed via scanning electron microscopy (SEM) in two carychiid species from the early Middle Miocene of Styria, SE Austria. The protoconchs of the shells of Carychiella eumicrum (Bourguignat 1857) and Carychium gibbum (Sandberger 1875) show different types of microstructure on the embryonic shell during ontogeny. Total, superficial punctate structure on the shell of Carychiella eumicrum contrasts with the protoconch–teleoconch demarcation (p/t boundary) observed on the protoconch of Carychium gibbum. Both species exhibit aragonitic microstructure. Diagenetic effects, prismatic, homogeneous and crossed lamellar microstructures are detectible in both species. Rheomorphic folding and dense pitting within the columella of Carychiella eumicrum suggest a structure–function relationship for tensile strength and bulk weight reduction in carychiid snails. We hypothesize that total superficial pitting on the shell of C. eumicum, seen here for the first time in the Carychiidae, suggests paedomorphosis as a life-history strategy to palaeoecological conditions of the Rein Basin during the early Middle Miocene.
Organisms produce elaborate mineral parts that defy the common traits of “inorganic” crystallization in many ways. Calcium carbonate minerals are mainly used by invertebrates to build skeletal, protective, and storage mineralized constructs. Three crystalline polymorphs: calcite, aragonite, and vaterite, along with transient and stable amorphous calcium carbonate (ACC) are used for specific functions. In this chapter recent insights into the biomineralization processes of calcium carbonate are presented. The control over crystal nucleation, growth, shape and internal symmetry of the crystalline elements are mediated by specialized biomacromolecules. Studies of organisms from diverse phyla have yielded several common features: Accumulation of material into the mineralization site is done by aggregation of amorphous nanometer sized spherules. Usage of transient amorphous material as a precursor phase is a general phenomenon. It allows molding the shape of the crystal into a desired form. Specific, glutamic acid-rich proteins interact with ACC and possibly prevent it from crystallization. Another set of highly acidic, aspartic acid rich-proteins interact specifically with the crystalline phases. Subsets of these acidic proteins constitute the crystal nucleation sites and the intracrystalline proteins and are specific for calcite versus aragonite formation. Specifically occluded, intracrystalline proteins modify the intrinsic texture of the biogenic crystals, increase their toughness and reduce the natural brittleness. Some aspects of biological mineral formation have been reproduced and studied in artificially deposited calcium carbonate in the presence of macromolecules extracted from biominerals or in synthetic analogous systems. The simple crystal habit of calcite facilitates the interpretation of the directional interactions it undergoes with synthetic compounds in vitro and provides systematic clues for the control mechanisms exerted by the organisms on the minerals they deposit.
Pojetaia and Fordilla are the oldest bivalve mol-luscs, occurring in roughly co-eval rocks from the Tommo-tian, and are the only undisputed, well-known bivalves from the Cambrian. New specimens reveal that Pojetaia had a laminar inner shell microstructure reminiscent of the foli-ated aragonite of modern monoplacophorans, and the same is true for Fordilla. A similar shell microstructure is seen in Anabarella and Watsonella, providing support for the hypothesis that they are the ancestors of bivalves. Foliated aragonite shares many similarities with nacre, and it may have been the precursor to nacre in bivalves. No cases of undisputed nacre occur in the Cambrian, in spite of much shell microstructure data from molluscs of this time period. Thus, although considered by many to be homologous among molluscs, we conclude that nacre convergently evolved in monoplacophorans, gastropods, bivalves, and cephalopods. This independent origin of nacre appears to have taken place during, or just prior to, the Great Ordovi-cian Biodiversification Event and represents a significant step in the arms race between predators and molluscan prey.
We examine the morphometric, chemical, and physical properties of adult shells from breeding populations of Cornu aspersum maxima (Taylor, 1883), Cornu aspersum aspersum (Müller, 1774), and Helix pomatia (Linnaeus, 1758). The higher thermal requirements of the African subspecies C. aspersum maxima were confirmed by the fact that normal shell maturation, indicated by a decreasing calcium content as the snail ages, was related to an increased mean air temperature of over 22.9 °C during the breeding season. In contrast, normal shell maturation of the European subspecies C. aspersum aspersum occurred with a temperature in the range of 20.6–23.6 °C. Based on the results of texturometric analysis, shell puncture force increased with an increase in temperature during breeding. In contrast, shell puncture force decreased and collapsing force increased with increasing relative humidity. The mechanical strength of C. aspersum and H. pomatia shells was related to their chemical composition and the level of their structural maturity. Shells containing a higher percentage of calcium were characterized by lower mechanical strength than those containing a lower amount.
Previous studies on the calcitic seminacre of the craniid brachiopod Novocrania have never fully resolved the crystallography of its constituent calcite crystals. With this aim, we studied the tablets forming the foliated-like and seminacre layers of this brachiopod by means of scanning electron microscopy coupled to electron backscatter diffraction. In both cases, tablets are monocrystalline and have a common crystallographic structure. Their c axes lie approximately parallel to the shell surface, and, for those tablets forming the internal shell ribs, they are also parallel to the rib elongation. There is no consistency in the orientation of the a axes in the different plates. Crystal competition processes appear to be responsible for this fiber texture. The tablets are bounded by planar rhombohedral faces. The main, innermost surface is not a crystal face but marks the boundary of the crystal with the mantle epithelium. Our data also show that, during spiral growth, the crystal axes of seminacre tablets remain stationary. Calcite twins occasionally develop in the species Novocrania anomala. The foliated-like and seminacre microstructures are crystallographically dissimilar to the foliated layer of molluscs but similar to the foliated layer of bryozoans. The relationship of brachiopod seminacre to the molluscan nacre is also discussed.
A large number of polycrystalline materials, both manmade and natural, display preferred orientation of crystallites. Such alignment has a profound effect on anisotropy of physical properties. Preferred orientation or texture forms during growth or deformation and is modified during recrystallization or phase transformations and theories exist to predict its origin. Different methods are applied to characterize orientation patterns and determine the orientation distribution, most of them relying on diffraction. Conventionally x-ray pole-figure goniometers are used. More recently single orientation measurements are performed with electron microscopes, both SEM and TEM. For special applications, particularly texture analysis at non-ambient conditions, neutron diffraction and synchrotron x-rays have distinct advantages. The review emphasizes such new possibilities.
A second section surveys important texture types in a variety of materials with emphasis on technologically important systems and in rocks that contribute to anisotropy in the earth. In the former group are metals, structural ceramics and thin films. Seismic anisotropy is present in the crust (mainly due to phyllosilicate alignment), the upper mantle (olivine), the lower mantle (perovskite and magnesiowuestite) and the inner core (ε-iron) and due to alignment by plastic deformation. There is new interest in the texturing of biological materials such as bones and shells. Preferred orientation is not restricted to inorganic substances but is also present in polymers that are not discussed in this review.
The crystallographic texture of nacre in eleven bivalve species belonging to the superorders Opponobranchia, Pteriomorpha, and Paleoheterodonta, was studied. Our analysis confirmed a uniform orientation of the crystallographic c-axes of aragonite platelets in all the species studied, but a variable arrangement of a-and b-axes. New data suggest that the rate of alignment of a-and b-axes from girdle-like (unordered nacre) to a single crystal-like texture (ordered nacre) differs considerably among the analyzed species. Numerical evaluation of the data obtained from species with ordered nacre also revealed systematic differences in texture strength among the main crystallographic axes of aragonite plate-lets. The texture strength of a-axes (direction parallel to growth lines) is always weaker than that of b-and c-axes. Ob-served differences in shape of the growth lines on the surface of nacreous platelets, in twinning percentage as well as in rate of alignment of a-and b-axes suggest variations in nacre growth process in individual phylogenetic lineages of the Class Bivalvia. These facts may imply not only evolutionary changes in microstructure and crystallographic texture of the nacre but also in molecular mechanisms driving its production during the long molluscan evolution. • Key words: Bivalvia, nacre, crystallographic texture, phylogeny.
The nacreous tablets in the Nautilus shell have similar crystalline structure as the tablets in the gastropod Gibbula shell. Etching with Mutvei's solution reveals that each tablet is composed of vertical crystalline columns that are structurally similar to the acicular crystallites in the outer spherulitic-prismatic layer of the shell wall. The columns are attached to each other to form numerous vertical crystalline lamellae, oriented parallel to the longitudinal axis of the tablet. It is still unknown whether or not the orientation of the vertical lamellae corresponds to that of the crystallographic a- or b-axis. The orientation of the crystalline lamellae in the adjacent tablets is parallel in some nacreous laminae, but random in other laminae. Similar large variation was found in the nacreous tablets of the gastropod and bivalve shells. The nucleation sites of the nacreous tablets are predominantly situated on the peripheral portion of the upper surface of the preceding tablet, both in the shell wall and septa. The "aragonite-nucleating proteins" in the central portion of the crystal imprints of the organic interlamellar sheets, described by several writers, have therefore a negative correlation with the nucleation sites of the nacreous tablets.
Methods to insert, keep and fix silver and gold nanoparticles to the inner walls of microstructured fibers are demonstrated. Fibers optimized for evanescent field interaction were employed and can result in efficient plasmonic chemical sensing.
Nacre, or mother-of-pearl, the tough, iridescent biomineral lining the inner side of some mollusk shells, has alternating biogenic aragonite (calcium carbonate, CaCO(3)) tablet layers and organic sheets. Nacre has been common in the shells of mollusks since the Ordovician (450 million years ago) and is abundant and well-preserved in the fossil record, e.g., in ammonites. Therefore, if any measurable physical aspect of the nacre structure was correlated with environmental temperatures, one could obtain a structural paleothermometer of ancient climates. Using X-ray absorption near-edge structure (XANES) spectroscopy, Photoelectron emission spectromicroscopy (PEEM), and X-ray linear dichroism we acquired polarization-dependent imaging contrast (PIC) maps of pristine nacre in cross-section. The new PIC-map data reveal that the nacre ultrastructure (nacre tablet width, thickness, and angle spread) is species-specific in at least eight mollusk species from completely different environments: Nautilus pompilius, Haliotis iris, Haliotis rufescens, Bathymodiolus azoricus, Atrina rigida, Lasmigona complanata, Pinctada margaritifera, and Mytilus californianus. Nacre species-specificity is interpreted as a result of adaptation to diverging environments. We found strong correlation between nacre crystal misorientations and environmental temperature, further supported by secondary ion mass spectrometry measurements of in situ δ(18)O in the nacre of one shell. This has far-reaching implications: nacre texture may be used as a paleothermometer of ancient climate, spanning 450 million years of Earth's history.
An analysis of the crystallographic texture of nacre (mother-of-pearl) in the Late Triassic gastropod <sub>Wortheniella coralliophila </sub>is presented. The primary aim of this study was to test the time stability of the crystallographic texture pattern of gastropod nacre over an extremely long time span. Our results show that the crystallographic axes of individual aragonite platelets in the Late Triassic <sub>Wortheniella coralliophila </sub>have an identical arrangement to those in living vetigastropods. The same microstructure as well as the crystallographic texture of nacre in Recent and Late Triassic gastropods implies the same biological mechanisms for its formation. Our study suggests that the proteins controlling the shape and orientation of individual nacreous platelets in living gastropods have not changed since the Late Triassic. The molecular mechanisms driving the origin and the development of gastropod nacre are thus extremely old and have remained unchanged for at least 220 million years.
Organic matrix was isolated from the shell of the bivalve Argopecten irradians by decalcification. The capacity of the matrix to initiate formation of crystals similar in form and orientation to the crystals of normal shell was investigated. Decalcified shell matrix placed in an inorganic recalcification solution initiated the formation of elongate crystals in parallel arrangement corresponding to the parallel orientation observed in the matrix fibers and similar to the orientation of the long crystals in normal shell. The detailed form of the crystals deposited in vitro was different from that of the normal shell crystals. Electron diffraction analysis of remineralized matrix demonstrated that the material was calcite, the mineral of normal shell.
In contrast, the calcareous tube of the serpulid Hydroides dianthus has crystals lacking uniform arrangement and a matrix which does not have a well-oriented structure. The decalcified tube matrix was recalcified and the mineral posited showed some evidence of normal orientation.
The results demonstrate that matrices of Argopecten shell and Hydroides tube can induce crystal formation in vitro. Since the soluble matrix would be expected to be removed during decalcification, the observed in vitro effects apparently involve the insoluble matrix.
The aragonite crystals in molluscan nacreous tablets show complicated twinning patterns when etched with a glutaraldehydeacetic acid solution. In the bivalves, Mytilus, Nucula and Unio, each tablet is composed of two layers. The outer layer consists of four, radially-arranged, crystal individuals which are probably cyclically twinned. The surface of this layer exhibits concentric growth lamellae. The surface of the inner layer shows numerous parallel crystalline laths which indicate a lamellar, polysynthetic twinning of this layer. These laths are associated with an organic matrix which remains after demineralization.
Determination and interpretation of the preferred orientation of crystals in deformed polycrystalline aggregates (in this volume also referred to as texture) has been of longstanding concern to both materials scientists and geologists. A similar theoretical background-such as the dislocation theory of crystal plasticity-has been the basis of understanding flow in metals and rocks; and similar determinative techniques-including microscopy and x-ray diffraction-have been used to study textures and microstructures. Whereas many of the fundamental principles have been established early this century by scientists such as Jeffery, Sachs, Sander, Schmid, Schmidt, and Taylor, only in recent years has knowledge reached a level that provides a quantitative framework which has replaced a largely phenomenological approach.
An orthorhombic structure α-chitin, probably in the form of a chitin-protein complex, was identified in the matrix of the shell of Anodonta cygnea by X-ray diffraction. Aragonite crystals of pseudohexagonal symmetry were also found by a Lauegram on the nacreous layer of the shell. The orthorhombic structure of these two compounds together with the identical reticular spacing d110 corroborate, in Anodonta cygnea, the indirect chitin-aragonite relationships already suggested for molluscan shells.
Observations with SEM in the inner surface of the shell showed CaCO3 crystals with irregular geometrical shapes in spring and summer and regular geometrical shapes in autumn and winter. The more elaborate aspect appearing in winter corresponds to an accurate hexagonal shape. This suggests that the observed variability may depend on the balance between calcium and hydrogen ions in the extrapallial fluid.
A cladistic analysis of the shell microstructures of Recent Vetigastropoda demonstrates, it is more parsimonious to assume
crossed lamellar shell structures, rather than nacreous, are plesiomorphic. The clade Vetigastropoda is characterized by having
intersected crossed platy shell structure. The analysis suggests resolution of the internal phylogeny of the Vetigastropoda,
particularly separation of a crown group with nacreous shells, composed of Haliotidae, Pleurotomariidae, Seguenziidae, Stomatellidae,
Trochidae, and Turbinidae, separated from an unresolved grade with cross lamellar structures, Fissurellidae, Osteopeltidae,
and Pseudococculin-idae. It is also suggested, that Phasianellidae is neither part of nor sister taxon to Turbinidae.
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