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Epithelial tissues provide an important barrier function in animals, but these tissues are subjected to extreme strains during day-to-day activities such as feeding and locomotion. Understanding tissue mechanics and the adaptive response in dynamic force landscapes remains an important area of research. Here we carry out a multi-modal study of a simple yet highly dynamic organism, Trichoplax adhaerens, and report the discovery of abrupt, bulk epithelial tissue fractures induced by the organism’s own motility. Coupled with rapid healing, this discovery accounts for dramatic shape change and physiological asexual division in this early-divergent metazoan. We generalize our understanding of this phenomenon by codifying it in a heuristic model focusing on the debonding–bonding criterion in a soft, active living material. Using a suite of quantitative experimental and numerical techniques, we demonstrate a force-driven ductile-to-brittle material transition governing the morphodynamics of tissues pushed to the edge of rupture.

Many marine invertebrates have larval stages covered in linear arrays of beating cilia, which propel the animal while simultaneously entraining planktonic prey. These bands are strongly conserved across taxa spanning four major superphyla, and they are responsible for the unusual morphologies of many invertebrate larvae. However, few studies have investigated their underlying hydrodynamics. Here, we study the ciliary bands of starfish larvae, and discover a beautiful pattern of slowly evolving vortices that surrounds the swimming animals. Closer inspection of the bands reveals unusual ciliary ‘tangles’ analogous to topological defects that break up and re-form as the animal adjusts its swimming stroke. Quantitative experiments and modelling demonstrate that these vortices create a physical trade-off between feeding and swimming in heterogeneous environments, which manifests as distinct flow patterns or ‘eigenstrokes’ representing each behaviour—potentially implicating neuronal control of cilia. This quantitative interplay between larval form and hydrodynamic function may generalize to other invertebrates with ciliary bands, and illustrates the potential effects of active boundary conditions in other biological and synthetic systems.