Self-organisation draws much attention in biotic systems as it can produce complexity at reduced developmental cost. We address this topic in the context of the microstructure of the sea urchin skeleton. This 3D structure, called stereom, is a porous meshwork made of calcite, whose surface is saddle-shaped and bears a peculiar curvature signature. Many studies have addressed the morphogenesis of the stereom, in different species and skeletal parts, showing that it forms via biomineralisation through a rich dynamics of branching and reconnection episodes. Yet, a global, mechanistic comprehension of how skeletonising cells control preferential mineral deposition is still lacking. In this project we will focus on the regeneration of adult sea urchin spines. Our main hypothesis is that skeletonising cells are entangled with the stereom local geometry and that this interaction is mediated by the cytoskeleton. The internship aims to experimentally characterise how the evolution of the stereom affect the cytoskeleton organisation and vice versa, using confocal microscopy. In parallel we want to build a numerical model to test if local cell-structure interaction can reproduce the final complexity.