Self-repairing symmetry in jellyfish*

Standing on a British shore a century ago, D'Arcy Thompson wondered whether the shape of a medusa can be likened to the equilibrium form of a gelatinous drop. While many study how animals get their shapes during development, less is understood about how or whether animal shape is regulated in adulthood. We pursue this question of animal shape regulation in the moon jellyfish, Aurelia aurita. Using grafting and mechanical modulations, we found that Aurelia shape is governed by a morphogenetic system with multiple equilibria – such that we can make jellyfish with various stable shapes, including oval, rectangular, and triangular. Further, combining experimental and mathematical analyses, we found evidence that the shape of a medusa is governed as a dynamic equilibrium of the underlying tissue mechanics. Thus, as Thompson envisioned, belying its calm majesty, the shape of jellyfish is not statically encoded, but rather a continual balancing act.