A new genus and species of tentaculitid, Hidagaienites arcuatus, is described from calcareous beds near the Carboniferous–Permian boundary in the Hida-Gaien Terrane, Central Japan. Its mode of occurrence excludes the possibility that the specimens are derived from older strata. Thus, this tentaculitid represents the youngest record of the class Tentaculitoidea, which was previously thought to have become extinct in the Late Devonian.