PATEK, S.N.*; KORFF, W.; CALDWELL, R.; Univ. of California, Berkeley; Univ. of California, Berkeley; Univ. of California, Berkeley: Springy saddles: a new model of energy storage in the mantis shrimp�s strike

Mantis shrimp (Stomatopoda) have specialized feeding appendages which are used for smashing shells or spearing fish. We measured the speed and forces generated by the smashing appendage of Odonodactylus scyllarus using digital high speed imaging (5000 frames per second) and a submerged load cell. In animals with body sizes ranging from 11-14 cm, O. scyllarus appendages moved at speeds exceeding 14 m/s with impact forces exceeding 400 N. Cavitation occurred just prior to impact in all strikes. A powerful energy storage mechanism is necessary to generate such fast and forceful movements; previous studies have proposed that the extensor apodeme and muscle fibers in the merus store this elastic energy. We propose that an additional mechanism of energy storage is necessary given the explosive energy produced during the stomatopod strike. Specifically, we identified a compressive spring located on the exoskeleton of the feeding appendage. This exoskeletal spring is shaped like a saddle, and thus forms a surface which effectively resists failure in compression and can potentially store substantial elastic energy.