Diarylamidines are a group of widely used small molecule drugs. One common use of diarylamidines is their pharmacological inhibition of ligand-gated cation channels, including tetrameric ionotropic glutamate receptors and trimeric degenerin/epithelial sodium channel/acid-sensing ion channels. Here, we discover a degenerin/epithelial sodium channel/acid-sensing ion channel from the brachiopod (lamp shell) Novocrania anomala, at which diarylamidines act as agonists. The channel is closely related to bile acid-gated, pH-gated, and peptide-gated channels but is not activated by such stimuli. We describe activation of the channel by diminazene, 4',6-diamidino-2-phenylindole, and pentamidine, examine several biophysical and pharmacological properties, and briefly explore the molecular determinants of channel activity with site-directed mutagenesis. We term this channel the diarylamidine-activated sodium channel.