Biomineralization By The Marine Tubeworm Hydroides Dianthus: Structure And Composition Of The Adhesive Cement

The structure and composition of the adhesive cement of Hydroides Dianthus was studied using a variety of characterization techniques, including XRD, FTIR, SEM, EDX, and AFM. The cement was determined to be a composite of inorganic CaCO3 crystals in an organic matrix, with the organic component making up only a small fraction of the material. Two polymorphs of CaCO3, in roughly equal proportions, were identified in both the tube shell and the cement via XRD and FTIR: aragonite (CaCO3), and magnesium calcite ((Ca,Mg)CO3). Electron microprobe and EDX measurements also confirmed the presence of magnesium. SEM imaging revealed two distinct crystal habits, and EDX measurements allowed for the identification of crystals with an acicular habit as aragonite, and crystals exhibiting a triangular layered structure as magnesium calcite. AFM measurements in sea water and in air were performed in order to determine the elastic moduli of the various components of the composite cement. For the inorganic component, moduli in the range of ∼3 GPa were observed in the wet state, and values in the range of ∼11 GPa were observed in the dry state, both of which are consistent with literature values for CaCO3.