Abstract: The water snail Pomacea canaliculata retracts the discoidal and multi-layered operculum to protect the soft body from being attacked by predators, and releases it when threats lifted. However, the duration of the operculum retraction is usually less than that of the operculum protraction. In this paper, we elucidate the biological compliant mechanism of the operculum. By using confocal laser scanning microscopy, we find that the operculum has compliant sandwiched layers between hard layers. The layered structure results in a compliant mechanism with a bidirectional stiffness for the locking and unlocking processes of the operculum. A mathematical model is derived to rationalize the bidirectional stiffness mechanism of the operculum. In addition, we carry out the experiments on the locking and unlocking processes. The experimental results show that the locking tension is about two-fifths of the unlocking tension of the operculum. Moreover, based on the mechanical properties of the operculum with the layered structure, we designed an operculum-inspired structure, which may have a variety of potential applications in combined driving patterns

Key words: Water snail , · Operculum , · Multi-layered structure , · Bidirectional stifness , · Compliant mechanism