Ultrastructure and Polyene Pigments of Giant Triton Snail Charonia tritonis (Gastropoda) Shells from the South China Sea

The giant triton snail Charonia tritonis is a marine large carnivorous gastropoda inhabiting in the Indo-Pacific Ocean. Their splendid and highly organized Charonia tritonis shells are attractive; however few studies have been conducted on shell ultrastructure and pigmentation. The arrangements of crossed-lamellar structures were distinctive for the giant triton snail shell, showing three layers of mineral structures in the cross-section. The 1st-order and 2nd-order lamellae of the shell were around 10–20 μm and the crystals in outer layers intersected at right angles in this species. They were identified as aragonite crystals by Raman scattering, and granular organic matrix were attached to the aragonite mineral phase closely. Furthermore, the dominant Raman spectra from polyene pigments in the shell were characterized at wavenumbers of 1123 cm⁻¹ and 1504 cm⁻¹, assigned to stretching vibrations of carbon-carbon single (C-C) and double (C=C) bonds, and the polyene chain was confirmed with 11–12 C-C bonds and 12–13 conjugated C=C bonds. The research will lay a foundation for exploring the relationship between the calcareous shell and the formation of shell color in the giant triton snail.