O. gracilis may refer to: * Obruchevichthys gracilis, an extinct tetrapod species from Latvia during the Late Devonian * Oceanites gracilis, the Elliot's storm-petrel, a seabird species * Oedipina gracilis, a salamander species found in Costa Rica and Panama * Omphalotropis gracilis, a gastropod species endemic to Guam * Ormosia gracilis, a legume species found only in Malaysia * Oxidus gracilis, the "greenhouse millipede", a widely introduced millipede associated with agricultural areas worldwide * Oxyopsis gracilis, the South American green mantis, a praying mantis species