Biomineral structure and crystallographic arrangement of cerioid and phaceloid growth in corals belonging to the Syringoporicae (Tabulata, Devonian–Carboniferous): a genetic reflection

Abstract

An extensive study of the microstructure, nanostructrure and crystallographic properties of six taxa belonging to four different genera of Devonian and Carboniferous Syringoporicae showing dense phaceloid (Pleurosiphonella), pseudocerioid (Neomultithecopora) and cerioid growth patterns (Roemeria and Roemeripora) has been done in order to disclose the similarities and differences in the growth processes at the biomineral scale and understand the growth processes that provide organisms with an evolutionary advantage to colonize different habitats. All the skeletons have similarities regarding the biocrystallization process, showing that the Syringoporicae skeletons are a product of matrix-mediated biocrystallization. Micro- and nanotextural features are common in all of the skeletons studied, showing that they were composed of hierarchical structures. All studied taxa possess a complex nanostructure composed of co-oriented rounded nanocrystals with different sizes and morphologies, depending on the taxon. The identified microstructures include granules, lamellae, fibres and hyaline elements. The crystallographic techniques demonstrate that all of them except the hyaline elements are biogenic in origin. Granules could be aborted fibres during the growth of two corallites in contact. On the other hand, the study of the biomineral properties suggests that the skeleton structure is a reflection of the genetic code. The median lamina was formed by the joint crystallization of both polyps at the same time. The variation in the internal structural organization (phaceloid, pseudocerioid or cerioid) was conditioned by the environment (stressful situations or feeding strategies); on the contrary, the final structure is controlled by genetics and their crystallographic properties are characteristic for each internal structural organization.