Chemical transmitters are either low-molecular-weight molecules or neuropeptides. As a general rule, neuropeptides activate only slow metabotropic receptors; to date only one exception to this rule is known: the peptide-gated ionotropic receptor FaNaC from snails. Until now FaNaC has been regarded as a curiosity and it was not known whether or not peptide-gated ionotropic receptors are also present in other animal groups. Nervous systems first evolved in Cnidarians, which extensively use neuropeptides. Here we report cloning from the freshwater cnidarian Hydra of a novel ion channel (Hydra Na channel, HyNaC) that is directly gated by the neuropeptides Hydra-RFamides I and II and is related to FaNaC. The cells expressing HyNaC localize to the base of the tentacles, adjacent to the neurons producing the Hydra-RFamides, suggesting that the peptides are the natural ligands for this channel. Our results suggest that neuropeptides were already used for fast transmission in ancient nervous systems.