Evidence of a Biogenic Mineralization Process in Vermetid Feeding Mucus as Revealed by Raman Spectroscopy and Scanning Electron Microscopy

ABSTRACT Using analytical (Raman spectroscopy) and imaging (scanning electron microscopy) approaches, we evidenced a biogenic mineralization process in the pedal mucus of the vermetids Eualetes tulipa and Petaloconchus varians. Raman spectra showed the presence of main bands around v1(CO) 1,085, n4(OCO) 717 and 705 cm-1 attributed to stretching modes of calcium carbonate crystallized as calcite and aragonite. SEM images showed the presence of aragonite needles and rhombohedral crystals of calcite in the mucus. Secondary nucleation from calcium carbonate precursors is the most probably pathway for the formation and growth of calcium carbonate crystals in feeding mucus of E. tulipa and P. varians. The tube-like shells of vermetids are very plastic. They are capable of continuously modify the direction of the shell aperture, remolding their tubes and building terminal structures. As a result, vermetid shells may act as exploratory tubes that allow the snail to profit from a better water flow, avoid obstacles and successfully compete for space. Such plasticity probably demands an extra supply of calcium carbonate, particularly when indeterminate growth is involved, as is the case for species of Eualetes and Petaloconchus; this would explain the functional significance of the biogenic calcium carbonate formation in the feeding mucus.