Electron microscopic studies on radular tooth formation in the snails Helix pomatia L. and Limax flavus L. (Pulmonata, Stylommatophora)

Abstract

The radular teeth are secreted at the posterior end of the radular gland and move slowly towards the buccal cavity where they start to function. Helix pomatia and Limax flavus were examined to determine whether the newly formed teeth already show their definite species specific shape, or whether they are gradually finished and moulded in the radular gland. Scanning electron micrographs of Helix pomatia show that teeth are secreted in the odontoblast region in their final form. Their surface is still uneven at the outset; the same is true for the newest teeth of Limax flavus. Older teeth ready for use have a smooth surface. This change seems to be brought about by secretory activity of the superior epithelium of the radular sac. Air-dried radulae, previously isolated by KOH maceration, show considerable artefacts at their posterior end. Maceration leads to shrinking of the newest teeth, but does not change their contours. The newly secreted but as yet unhardened teeth become greatly deformed during the drying process.