Evidence of a Biological Control over Origin, Growth and End of the Calcite Prisms in the Shells of Pinctada margaritifera (Pelecypod, Pterioidea)

Abstract

Consistently classified among the references for calcite simple prisms, the microstructural units that form the outer layer of the Pinctada margaritifera have been investigated through a series of morphological, crystallographical and biochemical characterizations. It is often said that the polygonal transverse shape of the prisms result from the competition for space between adjacent crystals. In contrast to this classical scheme the Pinctada prisms appear to be composed of four successive developmental stages from the concentrically growing disks on the internal side of the periostracum to the OPEN ACCESSMinerals 2014, 4 816 morphological, structural and compositional changes in both envelopes and mineral components at the end of the prisms. These latest structural and compositional changes predate nacre deposition, so that the end of prism growth is not caused by occurrence of nacre, but by metabolic changes in the secretory epithelium. This sequence makes obvious the permanent biological control exerted by the outer cell layer of the mantle in both organic envelopes and mineralizing organic phases.

The Marsh’s Membrane: A Key-Role for a Forgotten Structure

“…This means that the Marsh's membrane is involved in the mineralization process, a conclusion here confirmed (Fig. 37.2g-j) and by previous observations (Cuif et al 2014). One of the most striking features of the calcite prisms in Pinctada margaritifera is the microstructural change that regularly occurs after about 150 μm growth length.…”

“…37.2l), the prisms become polycrystalline (Fig. 37.2m) (Cuif et al 2011(Cuif et al , 2014Checa et al 2013). Such a coordinated change contradicts the theory of "crystal growth competition" that postulates a selection of the best oriented crystals leading to a progressive increase of the mean diameter in a given shell.…”

“…Pinctada calcite prisms are submitted to microstructural changes during aging (Cuif et al 2014), and composition of both the mineral and organic phases is modified before the occurrence of nacre deposition (Cuif et al 2011). Microstructural variations of the prisms during shell growth provide evidence for time-based genetically programmed secretion process.…”

Thermodynamic Aspects of Molluscan Shell Ultrastructural Morphogenesis

“…This hypothesis, although somewhat controversial, gained support by the study of the organic interprismatic matrix and its effect on the prismatic structure formation in a variety of organisms belonging to different orders and superfamilies of the bivalve subclass Pteriomorphia: Pinna rudis , Atrina pectinata , Pinctada margaritifera , Pteria hirundo , Pteria penguin , Vulsella vulsella , Isognomon isognomon and Ostrea edulis . Stressing that the organic matrix is formed before the space is filled with mineral, this work provided additional evidence (from the standpoint of kinetics and thermodynamics) to the occurrence of self‐assembly and curvature driven organic boundary motion during the formation of the prismatic structure in these shells.…”

Nanoscale assembly processes revealed in the nacroprismatic transition zone of Pinna nobilis mollusc shells

“…The switch from prismatically organized calcite to densely stacked aragonite tablets, that is, nacre 11 34 35 36 , is orchestrated by finely tuned secretion of organic and inorganic ingredients into an extracellular compartment—the so-called extrapallial space. The complex interplay between the organic and inorganic constituents then governs the formation of the mineralized shell matrix.…”