Locking of the operculum in a water snail: Theoretical modeling and applications for mechanical sealing

Abstract

How can a water snail lock its door by an operculum? In this theoretical and experimental combined research, we revealed this by dissection, modeling and validation with a 3D printed technique. The operculum is a corneous or calcareous trapdoor-like sheet which attaches to the upper surface of the water snail's foot. It can plug the shell aperture by retracting the soft body when a predator or environmental threat is encountered. For a water snail (Pomacea canaliculata), the operculum can be locked in its shell rapidly. By optical microscope images, we found the operculum of P. canaliculata is a multilayered disk with a thicker center and thinner edge, which may be functionally influential for successful closing and opening the trapdoor. We filmed the locking in opercula of living snails, and designed an experiment to measure the deformation of opercula on the dead samples. We propose one mathematical model to describe the connections among geometry, sectionalized stiffness and the force for locking. By using 3D printing technique, we designed an operculum inspired locking mechanism to validate the theories we proposed. Under the same normal force, the water leakage rate of the bio-inspired structure can be reduced to 99% compared to the disk with uniform thickness. Our results reveal that the snail's operculum not only develops a light-weight trapdoor, but a locking mechanism which could serve as a valuable model for designing compliant locking mechanisms.

Keywords: Laminated structure; Leakage rate; Locking mechanism; Operculum.