Snaps of a tiny amphipod push the boundary of ultrafast, repeatable movement

Surprisingly, the fastest motions are not produced by large animals or robots. Rather, small organisms or structures, including cnidarian stinging cells, fungal shooting spores, and mandible strikes of ants, termites, and spiders hold the world acceleration records. These diverse systems share common features: they rapidly convert potential energy - stored in deformed material or fluid - into kinetic energy when a latch is released. However, the fastest and smallest known movements often cannot be used multiple times, because mechanical components are broken or ejected. Furthermore, some of these systems must overcome the added challenge of moving in water, where high density and viscosity constrain acceleration at small sizes. Here we report the kinematics of repeatable, ultrafast snaps by tiny marine amphipods (Dulichiella cf. appendiculata). Males use their enlarged major claw, which exceeds 30% of body mass, to snap a 1 mm-long dactyl with a diameter equivalent to a human hair (184 ...令人意外的是，目前已知最快的运动并非由大型动物或机器人产生。恰恰相反，小型生物或结构——包括刺胞动物（cnidarian）刺细胞、真菌弹射孢子，以及蚂蚁、白蚁与蜘蛛的颚部撞击——保持着全球加速度纪录。这些多样的系统具备共同特征：当锁扣释放时，它们可将储存在变形材料或流体中的势能快速转化为动能。然而，这类已知最快且尺寸最小的运动往往无法重复使用，因为其机械组件会在运动中被破坏或弹出。此外，部分此类系统还需克服水下运动的额外挑战：水的高密度与高黏度会限制小型尺度下的加速度表现。本研究报道了小型海洋端足类动物（Dulichiella cf. appendiculata）可重复的超快速夹合运动的运动学特征。雄性个体借助其占体重比例超30%的巨型大螯，夹合长度为1毫米、直径与人发相当（约184……）的螯指。