Biological strategy for the fabrication of highly ordered aragonite helices: the microstructure of the cavolinioidean gastropods.

Antonio G Checa,Joaquín Ramírez-Rico,Elena Macías-Sánchez

doi:10.1038/srep25989

Abstract

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, every fibre has a differentiated organic-rich thin external band, which is never invaded by neighbouring fibres. In this way, fibres avoid extinction. These intra-fibre organic-rich bands appear on the growth surface of the shell as minuscule elevations, which have to be secreted differentially by the outer mantle cells. We propose that, as the shell thickens during mineralization, fibre secretion proceeds by a mechanism of contact recognition and displacement of the tips along circular trajectories by the cells of the outer mantle surface. Given the sizes of the tips, this mechanism has to operate at the subcellular level. Accordingly, the fabrication of the helical microstructure is under strict biological control. This mechanism of fibre-by-fibre fabrication by the mantle cells is unlike that any other shell microstructure.

Highlights

The monophyletic suborder Euthecosomata[7]
The aragonitic helical fibrous microstructure (AHFM) microstructure of cavolinioideans is unique in being composed of helical fibres that run from the external to the internal shell surface at the same time as they coil helically
The secretion of the AHFM is driven by sophisticated mechanisms that operate at the subcellular level

Summary

Introduction

The monophyletic suborder Euthecosomata[7]. The shells of the Euthecosomata are sensitive to rising levels of dissolved CO2, and it has become a target group of studies aiming to evaluate the future impact of rising CO2 atmospheric levels on calcifying organisms[8,9,10]. Some features are completely unlike those of other molluscan microstructures and provide evidence that the organism strictly dictates the path of every fibre through an intricate and elaborate strategy, thereby exerting a degree of control not found in any other microstructure. This is the first time that such a subtle organic control mechanism for the fabrication of a microstructure has been brought to light

Methods

Results

Discussion

Conclusion