The ability to sense mechanical stimuli is crucial for survival, but do disparate animal species share similar mechanisms for mechanoreceptor cell development and mechanosensation? Amongst vertebrates, a cell type known as a hair cell transduces certain mechanical stimuli through movement of stereocilia. The evolutionarily conserved transcription factor POU-IV (Brn3) is required in mammals for both embryonic hair cell stereocilia formation and adult mechanosensation. The sea anemone Nematostella vectensis is a member of Cnidaria, a sister group to Bilateria. Its tentacles respond to mechanical stimuli and contain a stereocilia-bearing cell type which is morphologically similar to vertebrate hair cells. However, whether cnidarian hair cells share developmental, functional, or genetic features with vertebrate hair cells was unclear. We found that Nematostella hair cells expressed POU-IV. We established a POU-IV CRISPR knockout line, and found that knockout animals lacked stereociliary rootlets. Knockout animals were significantly less responsive to mechanical stimuli compared with non-mutant littermates. A preliminary comparison of published transcriptomes from POU-IV mutants and specific cell populations revealed that differential expression of several vertebrate hair cell gene homologues correlated with presence of POU-IV and hair cells. Thus, there was a correlation between POU-IV expression, specific cell type morphology, gene expression, and mechanosensory behavior. The presence of shared features between cnidarian and vertebrate hair cells sheds light on a means by which an evolutionarily conserved transcription factor can affect sensory ability across distantly related species.