The architecture and operating mechanism of a cnidarian stinging organelle

The stingers of jellyfish, sea anemones and other cnidarians, known as nematocysts, are remarkable cellular weapons used for both predation and defense 1 . Nematocysts are specialized organelles which consist of a pressurized capsule containing a coiled harpoon-like thread 2 . These structures are in turn built within specialized cells known as nematocytes 3 . When triggered 4 , the capsule explosively discharges, ejecting the coiled thread which punctures the target and rapidly elongates by turning inside out in a process called eversion 5,6 . Due to the structural complexity of the thread and the extreme speed of discharge, the precise mechanics of nematocyst firing have remained elusive 7 . Here, using a combination of live and super-resolution imaging, 3D electron microscopy and genetic perturbations, we define the step-by-step sequence of nematocyst operation in the model sea anemone Nematostella vectensis . This analysis reveals the complex biomechanical transformations underpinning the operating mechanism of nematocysts, one of the nature’s most exquisite biological micro-machines. Further, this study will provide insight into the form and function of related cnidarian organelles and serve as a template for the design of bioinspired microdevices.