The functional relationship between ectodermal and mesodermal segmentation in the crustacean, Parhyale hawaiensis

► There is an attractive hypothesis that mesoderm segments autonomously and induces the ectoderm to segment in most arthropods. ► We tested this hypothesis in the crustacean Parhyale hawaiensis. ► We found that ectoderm segments autonomously. ► We found that mesoderm segmentation requires at least a permissive signal from the ectoderm.