Shell Ultrastructure Research Articles

Structure Characteristics of the <i>Hemifusus tuba</i> Conch Shell

The mollusk shell mobilizes calcium from environment for skeletal mineralization. This occurs through synthesizing solids in solution in the presence of organic molecules of specific interior regions of the conch shell. The ultrastructure of the Hemifusus tuba conch shell living in the Huang/Bo sea area is investigated in the paper. It is shown that the composition and microstructure of the mollusk shell vary in different positions. The prodissoconch shell consists only of aragonite with the crossed-lamellar microstructure. While the spiral shell and the body shell of the Hemifusus tuba conch shell are composed of one calcite layer and several aragonite layers. The calcite layer consists of cylindrical grains, but the aragonite layers are crossed-lamellar ultrastructure. The margin of shell aperture is only composed of calcite with cylindrical grains. This natural optimization of the shell microstructure is intimately due to the growth of the organic matrix. The process of growth allows a constant renewal of the material, thus enabling the functional adaptation of the shells.

First record of a bivalved larval shell in Early Cambrian tommotiids and its phylogenetic significance

Abstract: Brachiopods are marine Lophotrochozoa whose soft parts are enclosed in a bivalved shell. Although brachiopods are represented by a rich record from the Early Cambrian to the present, the origin of their bivalved body plan remains controversial. The Early Cambrian organophosphatic tommotiids Micrina and Paterimitra from Australia have been proposed as stem brachiopods. Here, we describe their earliest ontogeny, indicating that tommotiids possessed bivalved planktotrophic larvae. The curious combinations of characters in Micrina and Paterimitra indicate that they may belong to the stems of the Linguliformea and Rhynchonelliformea, respectively. The bivalved shell of adult living brachiopods may represent a plesiomorphic character retained from planktic tommotiid larvae; the crown group body plan of the Brachiopoda may have evolved through the paedomorphic retention of a bivalved larval state.

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

The mollusk shell mobilizes calcium from environment for skeletal mineralization. This occurs through synthesizing solids in solution in the presence of organic molecules of specific interior regions of the conch shell. The ultrastructure and microhardness of the Hemifusus tuba conch shell living in the Huang/Bo sea area are investigated in the paper. It is shown that the composition and microstructure of the mollusk shell vary in different positions. The prodissoconch shell consists only of aragonite with the crossed-lamellar microstructure. While the spiral shell and the body shell of the Hemifusus tuba conch shell are composed of one calcite layer and several aragonite layers. The calcite layer consists of cylindrical grains, but the aragonite layers are crossed-lamellar ultrastructure at three size scales. The minimum structure size (the third-order lamella) is at about 20 nm − 80 nm. The margin of shell aperture is only composed of calcite with cylindrical grains. This natural optimization of the shell microstructure is intimately due to the growth of the organic matrix. At different positions the microhardness of mollusc shell is different due to different crystal structures and crystal arrangements. The growth process of shells allows a constant renewal of the material, thus enabling their functional adaptation to external environments.

Elevated level of carbon dioxide affects metabolism and shell formation in oysters Crassostrea virginica (Gmelin)

Estuarine organisms are exposed to periodic strong fluctuations in seawater pH driven by biological carbon dioxide (CO2) production, which may in the future be further exacerbated by the ocean acidification associated with the global rise in CO2. Calcium carbonate-producing marine spe- cies such as mollusks are expected to be vulnerable to acidification of estuarine waters, since ele- vated CO2 concentration and lower pH lead to a decrease in the degree of saturation of water with respect to calcium carbonate, potentially affecting biomineralization. Our study demonstrates that the increase in CO2 partial pressure (pCO2) in seawater and associated decrease in pH within the environmentally relevant range for estuaries have negative effects on physiology, rates of shell depo- sition and mechanical properties of the shells of eastern oysters Crassostrea virginica (Gmelin). High CO2 levels (pH ~7.5, pCO2 ~3500 µatm) caused significant increases in juvenile mortality rates and inhibited both shell and soft-body growth compared to the control conditions (pH ~8.2, pCO2 ~380 µatm). Furthermore, elevated CO2 concentrations resulted in higher standard metabolic rates in oyster juveniles, likely due to the higher energy cost of homeostasis. The high CO2 conditions also led to changes in the ultrastructure and mechanical properties of shells, including increased thickness of the calcite laths within the hypostracum and reduced hardness and fracture toughness of the shells, indicating that elevated CO2 levels have negative effects on the biomineralization process. These data strongly suggest that the rise in CO2 can impact physiology and biomineralization in marine calcifiers such as eastern oysters, threatening their survival and potentially leading to profound eco- logical and economic impacts in estuarine ecosystems.

Mactra guidoin. sp. andMactra patagonica(Bivalvia: Mactridae), Two Long Misunderstood Species from Southwestern Atlantic Ocean

ABSTRACT A common mactrid from the southwestern Atlantic Ocean has been largely misunderstood in the literature. Since the early 20th century, this species has been referred to as Mactra patagonica d'Orbigny, 1846. However, the latter is recorded in Quaternary deposits of Northern Patagonia. Mactra guidoi n. sp. is described herein, including its shell ultrastructure, hinge features, and soft parts, and compared with the holotype of M. patagonica. To compare and to correctly identify both species, a morphometric analysis was carried out using conventional and geometric morphometric methods. Mactra guidoi n. sp. has an elongate shell that is more fragile than that of M. patagonica. In addition, its ventral posterior edge is usually sinuous. The ultrastructure of the shell reveals two layers with cross lamellar structure. The anatomical features agree with those of the congeneric M. isabelleana, although they differ in the morphology of the labial palps and foot. Morphometric analysis revealed significant d...

Control of crystal polymorph in microfluidics using molluscan 28 kDa Ca2+-binding protein

Biominerals produced by biological systems in physiologically relevant environments possess extraordinary properties that are often difficult to replicate under laboratory conditions. Understanding the mechanism that underlies the process of biomineralisation can lead to novel strategies in the development of advanced materials. Using microfluidics, we have demonstrated for the first time, that an extrapallial (EP) 28 kDa protein, located in the extrapallial compartment between mantle and shell of Mytilus edulis, can influence, at both micro- and nanoscopic levels, the morphology, structure and polymorph that is laid down in the shell ultrastructure. Crucially, this influence is predominantly dependent on the existence of an EP protein concentration gradient and its consecutive interaction with Ca²(+) ions. Novel lemon-shaped hollow vaterite structures with a clearly defined nanogranular assembly occur only where particular EP protein and Ca²(+) gradients co-exist. Computational fluid dynamics enabled the progress of the reaction to be mapped and the influence of concentration gradients across the device to be calculated. Importantly, these findings could not have been observed using conventional bulk mixing methods. Our findings not only provide direct experimental evidence of the potential influence of EP proteins in crystal formation, but also offer a new biomimetic strategy to develop functional biomaterials for applications such as encapsulation and drug delivery.

The curse of taxonomic uncertainty in biogeographical studies of free‐living terrestrial protists: a case study of testate amoebae from Amsterdam Island

AbstractAim A current debate in microbial biogeography contrasts two views concerning the distribution of free‐living microorganisms. The first view assumes a ubiquitous distribution, while the second assumes that at least some species have limited geographical distributions. We tested for limited geographical distributions by identifying testate amoebae morphospecies from an extremely remote oceanic island where the potential for endemism is high.Location Amsterdam Island, Indian Ocean.Methods Sixty moss and water samples collected from the top of the volcano to the lowland were investigated for their testate amoeba content. Due to taxonomic uncertainties among the Argynnia (Nebela) dentistoma species complex (including A. antarctica), we also performed light and scanning electron microscopy investigations on the shell ultrastructure and biometric analyses on several specimens of this taxon.Results We identified a total of 43 testate amoeba taxa belonging to 15 genera. Only four testate amoeba taxa had previously been recorded on this island. Testate amoeba communities of Amsterdam Island are dominated by cosmopolitan ubiquitous euglyphid taxa such as Trinema lineare, Assulina muscorum and Corythion dubium. The length and width ranges for Argynnia dentistoma on Amsterdam Island overlap with other records of this species and of A. antarctica, suggesting that A. antarctica is not a distinct taxon.Main conclusions Although Amsterdam Island is among the most remote islands in the world, an extensive inventory of testate amoeba morphospecies provided no clear evidence for endemism. On the one hand, our detailed morphometric analysis of the A. dentistoma complex revealed that A. antarctica, a morphospecies previously suggested to display endemism, cannot be confidently distinguished from the cosmopolitan morphospecies A. dentistoma. On the other hand, five morphotaxa could not be identified with certainty and might represent new species, potentially with limited distribution. These examples illustrate how taxonomic uncertainties undermine biogeographical studies of testate amoebae. In order to allow better interpretation of morphology‐based testate amoeba distribution data, an assessment of genetic diversity among and within morphotaxa in relation to geographical distance for some common testate amoebae should be given high priority.

Study on the relationship between eggshell colors and egg quality as well as shell ultrastructure in Yangzhou chicken.

Experiments were conducted to evaluate the relation between eggshell colors and egg quality as well as shell ultrastructure in Yangzhou chicken. A total of 120 eggs on the day of lay of New Yangzhou chickens were selected. The eggshell color, shape index, shell strength, shell thickness, egg weight, albumen weight, yolk weight, shell weight, yolk color, calcium content of shell, albumen and yolk were measured. Then the ultrastructure of transect and outer shell was observed through scan electron microscopy. The results showed that the tenderness of shell strength and shell thickness reduced as the shell color became shallow, however the pores in the shell and shape index increased. There were significant correlations between shell color and shell strength, shell thickness, and shell weight (P 0.05). It was concluded that some egg quality traits such as shell strength, shell thickness, shell weight and shell ultrastructure could be assessed through the shell color. Key words: Shell color, egg quality, ultrastructure, Yangzhou chicken.

Morphology, Biometry, and Taxonomy of Freshwater and Marine Interstitial Cyphoderia (Cercozoa: Euglyphida)

Good taxonomy is essential for ecological, biogeographical, and evolutionary studies of any group of organisms. Therefore, we performed detailed light- and scanning electron microscopy investigations on the shell ultrastructure and biometric analyses of the morphometric variability of five freshwater and marine interstitial testate amoebae of the genus Cyphoderia (C. trochus var. amphoralis, C. ampulla, C. margaritacea var. major, C. compressa, and C. littoralis), isolated from different populations in Bulgaria and Switzerland. Our aims were (1) to clarify the morphological characteristics of these taxa, and (2) to compare the morphology of a given taxon (C. ampulla) among different locations in Bulgaria and Switzerland as a first step towards an assessment of the geographical variation within a supposedly cosmopolitan taxon. Four of the studied taxa are characterized by a well-expressed main-size class and by a small size range of all the characters and can be defined as size-monomorphic species. Based on these results, the following systematic changes are proposed: C. major (Penard, 1891) n. comb. (Syn.: C. margaritacea var. major (Penard, 1891) and C. amphoralis (Wailes & Penard, 1911) n. comb. (Syn.: C. trochus var. amphoralis (Wailes & Penard, 1911)). However, we also show significant morphological variability between the Swiss and Bulgarian populations of C. ampulla, suggesting the possible existence of more than one taxon within this species. Further studies are required to assess (1) if these two morphologically different taxa represent individual species, (2) if so, if more species exist, and if this diversity is due to limited distribution ranges (endemism) or if several closely related taxa occur together in different geographical areas.

Crystallography of craniid brachiopods by electron backscatter diffraction (EBSD)

ABSTRACTElectron backscatter diffraction (EBSD) is used to determine the detailed crystallographic orientation of calcite crystals of craniid brachiopods in the context of shell ultrastructure. Sections of shells of two Recent species, Novocrania anomala and Novocrania huttoni, are analysed to provide 3D crystallographic patterns at high spatial resolution. The c-axis of semi-nacre calcite crystals is oriented parallel to the laminae that define the ultrastructure of the secondary layer. This orientation differs from that of rhynchonelliform calcitic brachiopods where the c-axis is perpendicular to the length of morphological fibres and to the shell exterior.

Closed-system behaviour of the intra-crystalline fraction of amino acids in mollusc shells

When mollusc shells are analysed conventionally for amino acid geochronology, the entire population of amino acids is included, both inter- and intra-crystalline. This study investigates the utility of removing the amino acids that are most susceptible to environmental effects by isolating the fraction of amino acids encapsulated within mineral crystals of mollusc shells (intra-crystalline fraction). Bleaching, heating and leaching (diffusive loss) experiments were undertaken on modern and fossil Corbicula fluminalis, Margaritifera falcata, Bithynia tentaculata and Valvata piscinalis shells. Exposure of powdered mollusc shells to concentrated NaOCl for 48h effectively reduced the amino acid content of the four taxa to a residual level, assumed to represent the intra-crystalline fraction. When heated in water at 140°C for 24h, only 1% of amino acids were leached from the intra-crystalline fraction of modern shells compared with 40% from whole shell. Free amino acids were more effectively retained in the intra-crystalline fraction, comprising 55% (compared with 18%) of the whole shell after 24h at 140°C. For fossil gastropods, the inter-shell variability in D/L values for the intra-crystalline fraction of a single-age population was reduced by 50% compared with conventionally analysed shells. In contrast, analysis of the intra-crystalline fraction of C. fluminalis does not appear to improve the results for this taxon, possibly due to variability in shell ultrastructure. Nonetheless, the intra-crystalline fraction in gastropods approximates a closed system of amino acids and appears to provide a superior subset of amino acids for geochronological applications.

CRYSTALLOGRAPHY AND DIAGENESIS IN FOSSIL CRANIID BRACHIOPODS

Abstract: One of the fundamental questions in biomineralization is how organisms control crystallographic orientation during biomineral production. The understanding of how diagenetic changes influence the preservation of original crystallographic patterns in fossilized biomineral structures provides a priori fundamental information for such an assessment. Fossil craniid brachiopods Petrocrania scabiosa (Late Ordovician) and Crania craniolaris (Late Cretaceous) are analysed using electron backscattered diffraction (EBSD) to provide crystallographic data at high spatial resolution in the structural context. EBSD analyses show that P. scabiosa maintains most of the original crystallographic signature, including data from individual calcite tablets and laminae, while C. craniolaris only retains fragmentary crystallographic data reflecting the crystallographic continuity of tablets across laminae. Data show that the preservation of the original crystallographic signature is independent of that of shell ultrastructure and geological time. In addition, results allow us to propose a series of steps in the evolution of ‘crystallographic loss’ due to diagenesis.

Taxonomic review of the Spixia pyriformis species complex (Gastropoda: Pulmonata: Odontostominae)

The genus Spixia (Pilsbry & Vanatta, 1898) is endemic from southern South America. Information about this group is scarce, particularly referring to its anatomy and shell ultrastructure. According to current classification the Spixia pyriformis complex includes the following species, S. doellojuradoi (Parodiz 1941), S. martensii (Doering 1874), S. pyriformis (Pilsbry 1901) and S. tucumanensis (Parodiz 1941). In the present study a complete redescription of the species component of this complex, as well as new information on shell ultrastructure and anatomy of the different organ systems is provided. The Spixia pyriformis complex has a pyriform-subpyriform shell shape that distinguishes it from the rest of the species of the genus. Three of the four species studied have a similar periostracum structure consisting of spiral striae and triangular lamellae. Radular morphology is similar in all species. Jaw structure is diagnostic for each species. The inner morphology of the penis is divided into five areas marked by differential pattern of sculpture. Four new anatomical characters, the presence of a pallial gland in the distal portion of the pulmonary roof, the presence of a penial gland in the penial complex, the position of the insertion of the penial retractor muscle in either penial area I or area II and the sculpture of penis inner wall, are identified as the most informative for species diagnosis.

Comparative observations on the cyst shells of seven Artemia strains from China

The quiescent Artemia cysts of seven geographical origins in China were examined with scanning and transmission electron microscopes. SEM observations on cysts of these Artemia strains showed that the surface topography of cyst shells could be categorized into 6 types: complete smooth surface; smooth surface with sparsely distributed glabrate humps; surface with densely arranged wart-like humps that are composed of packed minute tubercles; rugged surface, with densely arranged tubercles not piling up to form larger humps; shallow-pocked surface; and surface with numerous and densely spaced pore-like fossulae. Some of the patterns were strain specific [e.g., cysts from Ga Hai (GH) are characterized by having a surface with wart-like ornaments that are composed of packed minute tubercles, rugged surface is only found in Chengkou (CK) cysts], and apparent intrastrain variation of cyst surface topography was found in Xizang (XZ), Jingyu Hu, and Xie Chi (SIN) strains. TEM studies on the ultrastructure of cyst shells revealed an apparent divergence in the structure of outer cuticular membrane (OCM) among Artemia strains. In CK, Aqqikkol Hu (AQK), SIN, and GH strains, it is a normal, asymmetrical, and multi-layered structure similar to those described in previous works. In XZ, JYH, and Lagkor Co (LGC) strains, however, the OCM is not obviously multi-layered and the borderlines between OCM and adjacent layers seem indistinct. The present results suggest that the diversity of the surface topography of Artemia cysts may be an available tool for identifying certain Artemia strains as well as for tracking the origins of some Artemia cysts, and the hypoplastic OCM may be a characteristic of the species A. tibetiana.

Hatchability of Turkey Eggs as Dependent on Shell Ultrastructure

Hatchability of Turkey Eggs as Dependent on Shell Ultrastructure

Material properties of brachiopod shell ultrastructure by nanoindentation

Mineral-producing organisms exert exquisite control on all aspects of biomineral production. Among shell-bearing organisms, a wide range of mineral fabrics are developed reflecting diverse modes of life that require different material properties. Our knowledge of how biomineral structures relate to material properties is still limited because it requires the determination of these properties on a detailed scale. Nanoindentation, mostly applied in engineering and materials science, is used here to assess, at the microstructural level, material properties of two calcite brachiopods living in the same environment but with different modes of life and shell ultrastructure. Values of hardness (H) and the Young modulus of elasticity (E) are determined by nanoindentation. In brachiopod shells, calcite semi-nacre provides a harder and stiffer structure (H approximately 3-6 GPa; E=60-110/120 GPa) than calcite fibres (H=0-3 GPa; E=20-60/80 GPa). Thus, brachiopods with calcite semi-nacre can cement to a substrate and remain immobile during their adult life cycle. This correlation between mode of life and material properties, as a consequence of ultrastructure, begins to explain why organisms produce a wide range of structures using the same chemical components, such as calcium carbonate.

Ultrastructure of cyst shell and underlying membranes of three strains of the brine shrimp Artemia (Branchiopoda: Anostraca) from South India

The cyst of Artemia has shell and membranous coverings over the embryo. The membranous coverings have special adaptive features to allow the physical changes accompanying repeated hydration and dehydration cycles that might occur and adversely influence postembryonic development. Whole and slices of cryptobiotic cysts were processed for electron microscopy to study the internal details and to compare the morphological architecture of three Artemia strains of South India. Surface topography of scanning electron microscopic (SEM) studies revealed distinct button shaped structures on the cyst of Puthalam strain. Transmission electron microscopic (TEM) studies of the cysts displayed the conventional pattern of anostracan crustaceans with outer cortex and alveolar layer, cuticular membranes, and the cytoplasmic inclusions namely nucleus, yolk droplets, lipoid bodies, and mitochondria. The prominent wavy outer cortex layer of Puthalam cysts corroborates the results of SEM studies.

OBSERVATIONS ON THE MORPHOLOGY AND AFFINITIES OF CORNULITIDS FROM THE ORDOVICIAN OF ANTICOSTI ISLAND AND THE SILURIAN OF GOTLAND

The following differences were found between the members of the cornulitids, Cornulites and Conchicolites. Both genera have egg-shaped embryonic shells, which presumably calcified after the settling of larva to the substrate, but the embryonic shells in Cornulites are larger than in Conchicolites. Cornulites has a regularly foliated shell ultrastructure and pseudopuncta, whereas the shell ultrastructure in Conchicolites is prismatic. In Cornulites the outer part of the shell contains numerous vesicular cavities that were never observed to cross the interspaces of the surface annulae, indicating cyclic shell secretion. In several species the vesicles are internally coated by calcitic lamellae that are oriented subparallel to the shell surface. In Conchicolites the vesicular shell structure is absent and the calcitic prisms are deposited at the shell aperture more or less at right angles to the longitudinal shell axis. The function of the surface annulae in Cornulites and transverse ridges in Conchicolites may have been to strengthen the shell wall and protect it against longitudinally developing cracks. Vesicular structure in Cornulites seems to have provided a stronger shell for less material and smaller cost of energy. Differences between Cornulites and Conchicolites indicate that the two taxa were probably unrelated and that cornulitids may be a polyphyletic taxon. Cornulites shares the most characters with the lophoporates and tentaculitids. Biological affinities of Conchicolites are controversial, and its morphologic features need further revision to affiliate this group with certainty to any extant animal phylum.

Marine Myalinidae (Bivalvia: Pterioida) from the Permian of West Texas

Marine bivalves of the family Myalinidae are an important benthic constituent of the Permian Reef Complex of West Texas and New Mexico. We describe and summarize the myalinids from Lower and Middle Permian reef and near-reef settings and infer living habits as either epifaunal or semi-infaunal byssally attached suspension feeders. The six myalinid species described are exceptionally preserved as silica pseudomorphs. Included in the fauna are two new taxa: Myalina lamellosa, a species with distinctive commarginal lamellae, and Myalina plicata, the only known myalinid with prominent radial plicae. The family Myalinidae is placed in the Ambonychioidea (Order Pterioida) and an emended diagnosis incorporates ligament characters and details of shell ultrastructure.

Factors Affecting Egg Internal Quality and Egg Shell Quality in Laying Hens

Egg shell quality and egg internal quality are of major importance to the egg industry worldwide. This review covers the formation of the hen’s egg and ways of measuring egg shell quality and egg internal quality. Egg shell quality may be measured as egg size, egg specific gravity, shell colour, shell breaking strength, shell deformation (destructive or non-destructive), shell weight, percentage shell, shell thickness, and shell ultrastructure. New methods emerge from time to time. Egg internal quality is measured as yolk colour, the integrity of the perivitelline membrane, and albumen quality. Factors that affect egg shell quality and egg internal quality are reviewed. The complexity of the process of egg shell formation means that imperfections can arise in a number of places in the oviduct of the hen. Egg shell quality may be affected by the strain and age of hen ; induced moult ; nutritional factors such as calcium, phosphorus, vitamins, water quality, non-starch polysaccharides, enzymes, contamination of feed ; general stress and heat stress ; disease, production system, or addition of proprietary products to the diets. Egg internal quality may be affected by storage ; hen strain and age ; induced moult, nutrition, and disease. An understanding of the range of factors that affect egg shell quality and egg internal quality is essential for the production of eggs of high quality.