Antonio Checa

• Full Professor of Paleontology
• Professor (Full) at University of Granada

The microstructure of bivalve foliated calcite is extraordinary. It consists of units formed of stacks of folia with individual folia consisting of arrowhead-ended crystal laths. We investigated the texture of the foliated microstructure, the texture of individual and arrays of folia and the texture of assemblies of foliated units of the gryphaeid...

The shell of Ostreoidea is specific among that of bivalves, as it comprises many crystal microstructures and crystal textures. This stems from the fact that into the basic shell structure, consisting of columnar, foliated, granular calcite and myostracal aragonite, voids are incorporated: the pores of the vesicular segments and the blades/laths of...

Oysters inhabit a variety of coastal and deep‐sea settings over a wide latitudinal range and have a role as ecosystem engineers. They also represent an important food source for humans since hunter‐gatherer times, which motivates interest in using oyster shells as environmental and life history archives. Still, oysters have often been disregarded i...

Serpulid polychaetes are marine worms that secrete calcium carbonate tubes in which they live. Despite extensive previous research on their microstructures, there are no crystallographic data and their biomineralization process remains unclear. Here, the microstructures of the tubes of seven serpulid species were studied, including their chemical c...

Chamid bivalves are marine organisms that live in high-energy environments and are cemented to hard substrates. To avoid shell damage, the organisms form thick, densely ornamented shells. Shell material consists of aragonite, and the ornamentation may be either aragonitic or calcitic. The latter can be developed as scaly spines, rows of blades, or...

Caudofoveata are molluscs that protect their vermiform body with a scleritome, a mosaic of unconnected blade/lanceolate-shaped aragonite sclerites. For the species Falcidens gutturosus and Scutopus ventrolineatus we studied the crystallographic constitution and crystal orientation texture of the sclerites and the scleritome with electron-backscatte...

Gymnolaemata bryozoans produce CaCO3 skeletons of either calcite, aragonite, or both. Despite extensive research, their crystallography and biomineralization patterns remain unclear. We present a detailed study of the microstructures, mineralogy, and crystallography of eight extant cheilostome species using scanning electron microscopy, electron ba...

Serpulid polychaetes are global marine worms that secrete tubes of calcium carbonate, in which they live. Despite extensive previous research on their microstructures, there are no crystallographic data and their biomineralization process remains unclear. Herein, we review the microstructures of seven different serpulid species and study their chem...

Aplacophoran molluscs are shell-less and have a worm-like body which is covered by biomineralized sclerites. We investigated sclerite crystallography and the sclerite mosaic of the Solenogastres species Dorymenia sarsii, Anamenia gorgonophila, and Simrothiella margaritacea with electron-backscattered-diffraction (EBSD), laser-confocal-microscopy an...

Menilites, intriguing botryoidal rocks found in Galera, Granada, Spain, have been examined through a multidisciplinary approach integrating mineralogical analysis and advanced imaging techniques. Characterized as opal and dolomite-bearing rocks, their complex morphologies and diverse internal structures prompted an investigation into their origin....

The mechanism of nacre formation in gastropods involves a vesicular system that transports organic and mineral precursors from the mantle epithelium to the mineralization chamber. Between them lies the surface membrane, a thick organic structure that covers the mineralization chamber and the forming nacre. The surface membrane is a dynamic structur...

To construct their shells, molluscs are able to produce a large array of calcified materials including granular, prismatic, lamellar, fibrous, foliated, and plywood-like microstructures. The latter includes an aragonitic (the crossed-lamellar) and a calcitic (the crossed-foliated) variety, whose modes of formation are particularly enigmatic. We stu...

Planktonic gastropods of the suborder Euthecosomata (order Pteropoda) secrete a unique microstructure made of tightly interlocked, space-filling helically coiled aragonite fibers. This material has a high degree of ordering because all fibers are in phase at a given growth plane. The recognition of the helical nature from mere scanning electron mic...

More than half a billion years ago in the early Cambrian period, there began an evolutionary arms race between molluscs and their predators, in which molluscs developed armor in the form of a biomineral exoskeleton—a shell—to avoid being eaten by predators that were developing jaws and other novel means of devouring them. The mollusc fabricates mul...

Structural biological hard tissues fulfill diverse tasks: protection, defence, locomotion, structural support, reinforcement, buoyancy. The cephalopod mollusk Spirula spirula has a planspiral, endogastrically coiled, chambered, endoskeleton consisting of the main elements: shell-wall, septum, adapical-ridge, siphuncular-tube. The cephalopod mollusk...

Diversification of biocrystal arrangements, incorporation of biopolymers at many scale levels and hierarchical architectures are keys for biomaterial optimization. The planktonic rotaliid foraminifer Pulleniatina obliquiloculata displays in its shell a new kind of mesocrystal architecture. Shell formation starts with crystallization of a rhizopodia...

The vast majority of calcium carbonate biocrystals differ from inorganic crystals in that they display a patent nanoroughness consisting of lumps of crystalline material (calcite/aragonite) surrounded by amorphous pellicles. Scanning transmission electron microscopy coupled with electron energy loss spectroscopy (STEM-EELS) was used to map the calc...

The foraminiferal order Rotaliida represents one third of the extant genera of foraminifers. The shells of these organisms are extensively used to decipher characteristics of marine ecosystems and global climate events. It was shown that shell calcite of benthic Rotaliida is twinned. We extend our previous work on microstructure and texture charact...

We demonstrate that nature has produced a close-packed helical twisted filamentous material in the biomineralization of the mollusc. In liquid crystals, twist-bend nematics have been predicted and observed. We present and analyse evidence that the helical biomineral microstructure of mollusc shells may be formed from such a liquid-crystal precursor...

The endocochleate coleoid cephalopod Spirula spirula, the only present-day representative of the order Spirulida, secretes a coiled shell consisting of a series of chambers divided by septa and connected by a siphuncle. It is the shell closest to those of Recent and extinct ectochleate cephalopods: nautiloids, ammonoids. Therefore, its study may he...

The external surface microornament of the glass scallops Catillopecten natalyae and malyutinae is made by calcitic spiny projections consisting of a stem that later divides into three equally spaced and inclined branches (here called aerials). C. natalyae contains larger and smaller aerials, whereas C. malyutinae only secreted aerials of the second...

We analyzed, by optical and transmission electron microscopy, the morphology and function of the mantle edge, including the formation of the periostracum, of ten species of protobranchs. Five species from the order Nuculida, four species from the order Nuculanida and one species from the order Solemyida were studied. A second outer fold, which seem...

Diversification of biocrystal arrangement patterns, incorporation of biopolymers at many scale levels and a hierarchical architecture are keys for biomaterial optimization. In contrast to molluscan microstructures that consist of ordered assemblies of regularly shaped biocrystals, shells of modern rotaliid foraminifera comprise variously sized and...

The coleoid cephalopod Spirula spirula , the only present-day representative of the coleoid order Spirulida, secretes a coiled shell consisting of a series of chambers divided by septa and connected by a siphuncle. It is the shell closest to those of ectochleate cephalopods: nautiloids, ammonoids. Therefore, its study is crucial in understanding th...

Mollusks have developed a broad diversity of shelled structures to protect against challenges imposed by biological interactions(e.g., predation) and constraints (e.g., $$pCO_2$$ p C O 2 -induced ocean acidification and wave-forces). Although the study of shell biomechanical properties with nacreous microstructure has provided understanding about t...

The reinforcement function of shell ribs depends not only on their vaulted morphology but also on their microstructure. They are part of the outer layer which, in the case of the Pinna nobilis bivalve, is built from almost monocrystalline calcitic prisms, always oriented perpendicular to the growth surfaces. Originally, prisms and their c-axes foll...

The shell of the cephalopod Argonauta consists of two layers of fibers that elongate perpendicular to the shell surfaces. Fibers have a high-Mg calcitic core sheathed by thin organic membranes (>100 nm), and configurate a polygonal network in cross-section. Their evolution has been studied by serial sectioning with electron microscopy-associated te...

Shells of calcifying foraminifera play a major role in marine biogeochemical cycles; fossil shells form important archives for paleoenvironment reconstruction. Despite their importance in many Earth science disciplines, there is still little consensus on foraminiferal shell mineralization. Geochemical, biochemical, and physiological studies showed...

The shells of the bivalves Glycymeris glycymeris and Glycymeris nummaria are widely used for environmental studies. They consist of aragonite and comprise four different microstructures and textures from outer to inner shell surfaces: crossed-lamellar, myostracal, complex crossed-lamellar and fibrous prismatic. We characterize with SEM, EBSD, laser...

Here, we provide the dataset associated with the research article “Orientation patterns of aragonitic crossed-lamellar, fibrous prismatic and myostracal microstructures of modern Glycymeris shells” [1]. Based on several tools (SEM, EBSD, laser confocal microscopy and FE-SEM) we present original data relative to the microstructure and texture of ara...

The calcite grains forming the wall plates of the giant barnacle Austramegabalanus psittacus have a distinctive surface roughness made of variously sized crystalline nanoprotrusions covered by extremely thin amorphous pellicles. This biphase (crystalline-amorphous) structure also penetrates through the crystal’s interiors, forming a web-like struct...

Among bivalve muscles, the adductors are particularly important for animal survival because they control valve closure. Most studies have addressed the type and morphology of this muscle in bivalves but few have focused on the mechanism that anchors it to the shell myostracum layer. Moreover, the possible calcium transport mechanism through the add...

The vesicular microstructure is a very distinctive arrangement of calcite, consisting of hollow cavities (vesicles) of diverse sizes and shapes, usually elongated in the direction of shell thickening. It is uniquely found among living bivalves in a single oyster family, Gryphaeidae. The vesicles are distributed in lenses interleaved with compact fo...

Nacre, or mother of pearl, is a biomaterial with a layered structure. In a recent geological study, researchers found that the width of the nacre layers depends on the formation temperature, which is determined by the ocean water temperature. A linear dependence of layer width with respect to temperature is understandable within the transient liqui...

The shell structure of the Pinna nobilis species constitutes a model for others formed by bivalves of the Ostreida order. The outer part is built of monocrystalline columns whose axes remain parallel to the calcite c-axis. The present work reveals a new microstructure induced by mantle damage in the early stage of growth. The calcite c-axes, orient...

The reinforcement function of shell ribs depends not only on their vaulted morphology but also on their microstructure. They are part of the outer layer which, in the case of the Pinna nobilis bivalve, is built from almost monocrystalline calcitic prisms, always oriented perpendicular to the growth surfaces. Originally, prisms and their c-axes foll...

Stingless bees of the genus Tetragonula construct a brood comb with a spiral or a target pattern architecture in three dimensions. Crystals possess these same patterns on the molecular scale. Here, we show that the same excitable-medium dynamics governs both crystal nucleation and growth and comb construction in Tetragonula, so that a minimal coupl...

Many biological structures use liquid crystals as self-organizing templates for their formation. We review and analyse evidence that the crossed-lamellar biomineral microstructure of mollusc shells may be formed from such a liquid-crystal precursor. STATEMENT OF SIGNIFICANCE: Many biological structures use liquid crystals as self-organizing templat...

An organic-rich columnar prismatic outer shell layer, which extends far beyond the underlying nacre, has allowed pterioid bivalves (the pearl oysters and their allies) to develop flexible valve margins, allowing a tight hermetic seal when shut. In some taxa, the microstructural arrangement is known to be asymmetrically developed between the two val...

Cupitheca is an enigmatic tubular fossil common in early Cambrian deposits worldwide. It has recently been argued to be a hyolith, probably orthothecid. Cupitheca had a dense network of mantle-filled tubules that connected to what we interpret as a continuous organic periostracum. The innermost shell layer consists of horizontal or slightly incline...

The mechanical properties such as compressive strength and nanohardness were investigated for Pinctada margaritifera mollusk shells. The compressive strength was evaluated through a uniaxial static compression test performed along the load directions parallel and perpendicular to the shell axis, respectively, while the hardness and Young modulus we...

In biomineralization, it is essential to know the microstructural and crystallographic organization of natural hard tissues. This knowledge is virtually absent in the case of barnacles. Here, we have examined the crystal morphology and orientation of the wall plates of the giant barnacle Austromegabalanus psittacus by means of optical and electron...

The morphology and ultrastructure of the shells of two balanid species have been examined, paying special attention to the three types of boundaries between plates: (i) radii-parietes, (ii) alae-sheaths, and (iii) parietes-basal plate. At the carinal surfaces of the radii and at the rostral surfaces of the alae, there are series of crenulations wit...

Microstructure studies of various classes of materials show the presence of a strictly defined order. The basic structural elements, crystallites of the same or different phases, strive to determine the state with the smallest free energy. This leads to a special mutual misorientation of the neighboring grains. In the frame of the research electron...

Exceptional sub-micrometer details of shell microstructure are preserved in phosphatic micro-steinkerns representing several phyla from shell beds of the Upper Ordovician of the Cincinnati Arch region, USA. These fossils provide the most detailed record of Ordovician mollusk shell microstructures, as well as exceptional details on the earliest case...

The fibrous calcite layer of modern brachiopod shells is a hybrid composite material and forms a substantial part of the hard tissue. We investigated how cells of the outer mantle epithelium (OME) secrete calcite material and generate the characteristic fibre morphology and composite microstructure of the shell. We employed AFM, FE-SEM, and TEM ima...

Foliated calcite is widely employed by some important pteriomorph bivalve groups as a construction material. It is made from calcite laths, which are inclined at a low angle to the internal shell surface, although their arrangement is different among the different groups. They are strictly ordered into folia in the anomiids, fully independent in sc...

Nanoscale details of original aragonite crystals and organic inclusions are preserved in shells from the Pennsylvanian Buckhorn Asphalt of Oklahoma, USA. Exceptional preservation occurred because, either during or shortly after deposition, oil migrated along wrench faults generated during the simultaneous Ouachita Orogeny. The early sealing by oil...

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 fabrica...

Oyster shells are mainly composed of layers of foliated microstructure and lenses of chalk, a highly porous, apparently poorly organized and mechanically weak material. We performed a structural and crystallographic study of both materials, paying attention to the transitions between them. The morphology and crystallography of the laths comprising...

Organization of nanosized entities across many length scales poses a major challenge in the development and production of man-made materials with advanced functions. In contrast, in biologically formed hard tissues, this design feature and its formation principle is intrinsic. It began already with the emergence of first skeletal hard parts in late...

Currently a basic tenet in biomineralization is that biominerals grow by accretion of amorphous particles, which are later transformed into the corresponding mineral phase. The globular nanostructure of most biominerals is taken as evidence of this. Nevertheless, little is known as to how the amorphous-to-crystalline transformation takes place. To...

To achieve a better understanding of the formation and evolutionary history of molluscan shell microstructures, we analysed crystallographic textures of shell microstructures of selected species of Protobranchia, the most ancient group of Bivalvia. Our dataset covers four of the five protobranch superfamilies. Shell layers of five species of Nuculo...

Multiple groups of bivalve molluscs produce calcitic shell layers, many of these broadly classified as “pris-matic.” Various pteriomorphian bivalves (such as oysters, pterioids, and mussels) secrete prismatic microstructures with high organic content and clear, strong biological control. However, we present the results of a detailed analysis by sca...

The plesiomorphic state of the molluscan scleritome remains ambiguous. Chitons are significant because they show a mix of characters considered diagnostic in both aplacophorans and conchiferans, with both shell plates and small calcified girdle elements on an elongate body, and there is no consensus on the homology of structures involved in chiton...

Unlabelled: We show with laboratory experiments that self-assembled mineral tube formation involving precipitation around a templating jet of fluid - a mechanism well-known in the physical sciences from the tubular growth of so-called chemical gardens - functions with carbonates, and we analyse the microstructures and compositions of the precipita...

The Cavolinioidea are planktonic gastropods which construct their shells with the so-called aragonitic helical fibrous microstructure, consisting of a highly ordered arrangement of helically coiled interlocking continuous crystalline aragonite fibres. Our study reveals that, despite the high and continuous degree of interlocking between fibres, eve...

The degree to which biological control is exercised compared to physical control of the organization of biogenic materials is a central theme in biomineralization. We show that the outlines of biogenic calcite domains with organic membranes are always of simple geometries, while without they are much more complex. Moreover, the mineral prisms enclo...

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...

It is known for a long time that calcified tissues secreted by aquatic or terrestrial invertebrates – such as mollusc shells – have the ability to concentrate large amounts of pollutants, in particular heavy metals. In the present paper, we have found an extremely rapid and easy procedure to qualitatively detect the putative presence of heavy metal...

The surface membrane is a lamellar structure exclusive of gastropods that is formed during the shell secretion. It protects the surface of the growing nacre and it is located between the mantle epithelium and the mineralization compartment. At the mantle side of the surface membrane numerous vesicles provide material, and at the nacre side, the int...

To infer the early evolution of mollusc shell microstructures we must know the most ancient fossil record of molluscs. Fortunately the shells of many early molluscs are preserved via internal coatings and replacements by apatite that record sub-micrometer structural details that otherwise would be lost during diagenetic recrystallization. We herein...

Bivalve shell microstructures are important traits that can be used for evolutionary and phylogenetic studies. Here we examine the crossed lamellar layers forming the shells of the arcoids, Arca noae, Glycymeris glycymeris and Glycymeris nummaria in order to better understand the crystallography of this complex biomaterial. Textural aspects and cry...

The microstructures of different groups of molluscs are characterized by preferential orientations of crystallites (texture), leading to a significant anisotropy of the physical properties of the shells. A complementary characteristic, usually neglected, is the distribution of the residual stresses existing within the shell wall. By means of X-ray...

The pteropod Cuvierina constructs very lightweight, thin, flexible, and resistant shells with the most unusual microstructure: densely packed, continuous crystalline aragonite fibers that coil helically around axes perpendicular to the shell surface. The high degree of fiber intergrowth results in a particular interlocking structure. The shell is c...

Cuttlebone, the sophisticated buoyancy device of cuttlefish, is made of extensive superposed chambers that have a complex internal arrangement of calcified pillars and organic membranes. It has not been clear how this structure is assembled. We find that the membranes result from a myriad of minor membranes initially filling the whole chamber, made...

The current model for the ultrastructure of the interlamellar membranes of molluscan nacre imply that they consist of a core of aligned chitin fibers surrounded on both sides by acidic proteins. This model was based on observations taken on previously demineralized shells, where the original structure had disappeared. Despite other earlier claims,...

Mackinnonia davidi from the Cambrian (Series 2) of Australia has a prismatic outer shell layer and, as newly described here, a calcitic semi-nacre inner layer. The pattern is the same as in stenothecids such as Mellopegma, providing more evidence for a strong phylogenetic signal in the shell microstructure of Cambrian molluscs. In addition, calcite...

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 ar...

{110} twin density in aragonites constituting various microstructures of molluscan shells has been characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM), to find the factors that determine the density in the shells. Several aragonite crystals of geological origin were also investigated for comparison. The twin densi...

We investigated the spikes on the outer shell surface of the endolithic gastrochaenid bivalve genus Spengleria with a view to understand the mechanism by which they form and evaluate their homology with spikes in other heterodont and palaeoheterodont bivalves. We discovered that spike formation varied in mechanism between different parts of the val...

A detailed investigation of the shell formation of the palaeoheterodont 'living fossil' Neotrigonia concentrated on the timing and manufacture of the calcified 'bosses' which stud the outside of all trigonioid bivalves (extant and fossil) has been conducted. Electron microscopy and optical microscopy revealed that Neotrigonia spp. have a spiral-sha...

The calcitic prismatic units forming the outer shell of the bivalve Pinctada margaritifera have been analysed using scanning electron microscopy-electron back-scatter diffraction, transmission electron microscopy and atomic force microscopy. In the initial stages of growth, the individual prismatic units are single crystals. Their crystalline orien...

Nacre tablets of mollusks develop two kinds of features when either the calcium carbonate or the organic portions are removed: (1) parallel lineations (vermiculations) formed by elongated carbonate rods, and (2) hourglass patterns, which appear in high relief when etched or in low relief if bleached. In untreated tablets, SEM and AFM data show that...