Few animals have been as valuable to science as sea urchins. These spiky invertebrates have been used to study fertilization and embryogenesis, and the mechanical properties of their spines have been long admired1. Now, writing in Nature, Chen et al.2 report that sea-urchin spines, which are made up of a ‘stereom’ structure that includes interconnected struts and holes3, can generate voltages in response to water flow. This phenomenon, called mechanoelectrical sensing, arises because of size gradients in the stereom. Sea urchins were known to be sensitive to touch, changes in light intensity, temperature and the orientation of their bodies, but mechanoelectrical sensing, which, the authors argue, makes the spines sensitive to water flow, has not been observed before. The principle behind this could be used to make devices for underwater flow sensing.…