Radular sac, partially lost during dissection.
1: white ventral surface of sac. 2: intact section of roof of sac.
Tooth creation starts at the white, inner end (3) of the long radular sac with secretion of colourless transparent cuticular material by odontoblast cells. As each new tooth commences the previous one is pushed forwards along the sac. Cells along the roof of the sac (2) make incremental additions, including the hardening salts of iron and silicon, to the teeth as they travel along the sac, with a progressive change from colourless through darkening shades of yellow/orange visible through the translucent sac walls. The process is complete by the time the tooth reaches the buccal cavity, where it emerges from the radular sac onto the dorsal surface of the odontophore (4).
APPENDIX re range advance/retreat: flic.kr/p/2jW74ig