Radulae after removal of radular sac with 10% solution NaOH.
Left: from shell 13.2mm long. Retains four folds needed to fit the radula in the body.
Right: from shell 13mm long.
Like other limpets, and some sea snails, that graze rock surfaces, T. testudinalis has a radula considerably longer than its shell. To fit it inside the body it requires several folds. The cause of this correlation between length and rock grazing is uncertain. It may be that a lengthy process is needed for the teeth to acquire the required hardening mineralization.
APPENDIX re range advance/retreat: flic.kr/p/2jW74ig