The sea anenome Nematostella vectensis belongs to the Cnidaria phylum, which split from the Bilateria 600 million years ago. Similar to several basal bilaterian species, its larvae have an apical ciliary organ,which is believed to detect conditions suitable for metamorphosis. In their study of FGF signalling in N. vectensis development (see p. 1761), Fabian Rentzsch and colleagues used morpholino-mediated knockdown to analyse the function of two FGF ligands, NvFGFa1 and NvFGFa2, and of the NvFGFRa receptor. Their findings show that NvFGFa1 signalling via NvFGFRa is required for apical organ formation and that NvFGFa1 knockdown blocks metamorphosis. They also show that NvFGFa1 not only activates its own expression but also that of the antagonistic NvFGFa2, which possibly binds to NvFGFRa, without activating it,to restrict NvFGFa1's initially broad expression and to prevent ectopic organ formation. These findings provide the first known example of two FGF ligands that have activating and inhibiting effects consistent with a reaction-diffusion mechanism, and highlight an ancestral FGF signalling function.