Alexander D. Ball

Structure and composition of the nacre-prisms transition in the shell of Pinctada margaritifera (Mollusca, Bivalvia)

A microstructural, mineralogical, and chemical study of the nacre–prisms boundary in the shells of Pinctada margaritifera shows that this boundary is not an abrupt transition, but that there exists a distinct fibrous layer with clear topographic structures and evidence of growth lines. A three-step biomineralization process is proposed that involves changes in the chemical and biochemical composition of the last growth increments of the calcite prisms, formation of the fibrous layer, and development of regular tablets in the nacreous layer.

Ancient fig wasps indicate at least 34 Myr of stasis in their mutualism with fig trees.

Fig wasps and fig trees are mutually dependent, with each of the 800 or so species of fig trees (Ficus, Moraceae) typically pollinated by a single species of fig wasp (Hymenoptera: Agaonidae). Molecular evidence suggests that the relationship existed over 65 Ma, during the Cretaceous. Here, we record the discovery of the oldest known fossil fig wasps, from England, dated at 34 Ma. They possess pollen pockets that contain fossil Ficus pollen. The length of their ovipositors indicates that their host trees had a dioecious breeding system. Confocal microscopy and scanning electron microscopy reveal that the fossil female fig wasps, and more recent species from Miocene Dominican amber, display the same suite of anatomical characters associated with fig entry and pollen-carrying as modern species. The pollen is also typical of modern Ficus. No innovations in the relationship are discernible for the last tens of millions of years.

Micro-computed X-ray tomography: a new non-destructive method of assessing sectional, fly-through and 3D imaging of a soft-bodied marine worm

The detailed examination of the internal and functional anatomy of soft‐bodied marine worms has, until now, only been possible using the time consuming and destructive techniques of dissection, histology and electron microscopy. This is the first description of soft body morphology in polychaetes (Nephtys hombergii) derived by means of a bench‐top X‐ray micro‐CT scanner. The data are augmented, for comparison, by dissections, microscopy and scanning electron microscopy of the same species to show how this non‐destructive technique can rapidly and reliably produce high‐quality morphological data. It can also be applied to rare or unique invertebrate soft tissue material from museum collections and also to large‐scale invertebrate comparative anatomical studies possibly leading to greater evolutionary and taxonomic understanding. High‐definition images were obtained without the use of special tissue enhancing stains or radio‐opaque fluids and it is believed that this is the first time the technique has been successfully applied to this group of invertebrates. Extrapolation of the sectional imaging of regions of the gut and the production of three‐dimensional rotating and ‘fly‐through’ imaging can assist in assessment of aspects of functional anatomy.

MORPHOLOGY AND POSTLARVAL DEVELOPMENT OF THE LIGAMENT OF THRACIA PHASEOLINA (BIVALVIA: THRACIIDAE), WITH A DISCUSSION OF MODEL CHOICE IN ALLOMETRIC STUDIES

The ligamental apparatus of Thracia comprises external and internal resilient components, as well as a calcified ossicle termed the lithodesma. All these elements have hitherto been considered portions of a single unit and their allometry and functional morphology interpreted as such. However, analyses of the fine structure of the hinge of a growth series of Thracia phaseolina using conventional light, confocal and scanning electron microscopy revealed that, instead, external and internal components comprise distinct, independent layers of fibrous ligament, each formed at different ontogenetic stages. The internal ligament, with a lithodesma along its mid-sagittal sector, comprises the sole early juvenile ligament of the species and its main function is to force the shell valves open, not align them as had been previously suggested. The external (parivincular) ligament only appears at a shell length of c. 2.5 mm, but grows faster than the internal ligament to become the main component of the hinge of adults. Two- and three-parameter power functions (simple and full allometric equations) were fitted to measurements of the different ligament parts, and the performance and appropriateness of these models in describing the allometry of each of the studied traits are evaluated. Use of the full allometric model is recommended whenever the body size (or other standard) at which a trait of interest arises lies within or close to the limits of the sampled range.

Hierarchical structure of marine shell biomaterials: biomechanical functionalization of calcite by brachiopods

Abstract Biologic structural materials for skeletons or teeth show a hierarchical architecture, where organic macromolecules and mineral substance form a hybrid composite material with its components inter-weaved on many length scales. On the nanostructure level brachiopods form hybrid composite mesocrystals of calcite with occluded organic molecules. On the microstructure level several types of materials are produced, on which the electron back-scatter diffraction (EBSD) technique gives insight in texture and architecture. We describe the calcite single-crystal fiber composite architecture of the secondary layer involving organic matrix membranes, the competitive-growth texture of the columnar layer and the nano-structuring of the primary layer. In the overall skeleton the organic biopolymers provide flexibility and tensile strength while the mineral provides a high elastic modulus, compressive strength, hardness and resistance to abrasion. The hierarchical composite architecture, from the nanostructure to the macroscopic level provides fracture toughness. The morphogenesis of the biomaterial as a whole and of the mineral crystals is guided by the organic matrix and most probably involves amorphous calcium carbonate (ACC) precursors. In this paper we review the hierarchical architecture of rhynchonelliform brachiopod shells, which is very distinct from mollusk nacre.

Structural, Mineralogical, and Biochemical Diversity in the Lower Part of the Pearl Layer of Cultivated Seawater Pearls from Polynesia

A series of Polynesian pearls has been investigated with particular attention to the structural and compositional patterns of the early developmental stages of the pearl layer. These initial steps in pearl formation bear witness of the metabolic changes that have occurred during the pearl-sac formation. The resulting structurally and biochemically complex structures have been investigated using a variety of techniques that provide us with information concerning both mineral phases and the organic components. Results are discussed with respect to our understanding of the biomineralization mechanisms, as well as for the grafting process.

Towards systematics of calcite biocrystals: insight from the inside

Abstract Biocrystals of calcite are frequent as they are employed by many phylae of organisms in shells, eggshells, teeth, spines or sensoric apparatus. The calcite phase in these materials occurs in a range of constitutions, from polycrystalline fabrics to “single-crystals”. We demonstrate systematics of calcite biocrystal architectures, from the hybrid composite mesocrystal fibres of brachiopod and mollusc shells, via the submillimeter-sized hybrid composite crystal aggregates formed by mesocrystal fibres with both morphological co-orientation and lattice co-oriäentation, to more complex purpose-oriented multiplex äcomposite crystals of echinoderm teeth, which feature a high degree of single-crystal-like 3D orientational correlation of microstructural elements of different morphology and composition. These systematics rely on observations by electron backscatter diffraction (EBSD) and TEM.

Subdaily growth patterns and organo-mineral nanostructure of the growth layers in the calcitic prisms of the shell of Concholepas concholepas Bruguière, 1789 (Gastropoda, Muricidae).

Fluorochrome marking of the gastropod Concholepas concholepas has shown that the prismatic units of the shell are built by superimposition of isochronic growth layers of about 2 mum. Fluorescent growth marks make it possible to establish the high periodicity of the cyclic biomineralization process at a standard growth rhythm of about 45 layers a day. Sulphated polysaccharides have been identified within the growth layers by using synchrotron radiation, whereas high resolution mapping enables the banding pattern of the mineral phase to be correlated with the layered distribution of polysaccharides. Atomic force microscopy has shown that the layers are made of nanograins densely packed in an organic component.

Deciphering the distribution of organic components in brachiopod shells by confocal laser scanning microscopy

Characterization of the nature and distribution of organic components is crucial to understand shell formation in marine invertebrates. Although several techniques can provide detailed information at high spatial resolution, few of them are non‐destructive and informative in a larger structural context. We explore the use of confocal laser scanning microscopy (CLSM) to obtain a better understanding of the distribution of organic components in calcitic shells of brachiopods focusing on perforations (punctae) across the shell. Resulting intensities and patterns of fluorescence correspond well with the distribution of polysaccharides and proteins as reported in previous histological and biochemical studies. Confocal laser microscopy is, therefore, a useful tool to be combined with other techniques to improve our knowledge of biomineral structures in marine invertebrates.

Characterization of the green iridescence on the chelicerae of the tube web spider, Segestria florentina (Rossi 1790) (Araneae, Segestriidae)

Abstract Segestria florentina (Rossi 1790) (Segestriidae) displays iridescent green coloration on the paturons of the chelicerae. This was confirmed by reflectance measurements, which gave a spectral peak at 505 nm. Scanning electron microscopy did not identify cuticular surface scales or sculpturing, suggesting that the cause of the iridescence was subsurface. Transmission electron microscopy revealed 86 alternate dark and light layers in the exocuticle, the mean dimensions of which were 126 nm ± 28 nm and 88 nm ± 55 nm respectively. The identity of each layer was initially unclear. However, by using a combination of materials with different refractive indices in calculations of theoretical reflectance spectra, we concluded that they were most likely to be composed of chitin and air, since a peak of 480 nm was obtained, which most closely matched that which was recorded. The function of the green color is not clear, since S. florentina has relatively poor vision and relies predominantly on vibratory and acoustic signals. The study provides useful information relevant to research into the evolution of structural colors in spiders and, more generally, in nature.