Animals come in an extraordinary range of body shapes. A starfish looks nothing like an earthworm, a mouse, or a human. Yet even closely related species can appear radically different: corals, jellyfish, and sea anemones all belong to the same biological phylum, but their bodies take strikingly different forms. A new study by EMBL researchers and their collaborators at the University of Geneva, appearing in Cell, shows how such shape diversity is determined by variation in mechanical tissue properties—an idea they termed "mechanotypes."