One of the two tentacle-like organs on the back of the head or neck of a nudibranch or tectibranch mollusk. They are usually retractile, and often transversely furrowed or plicate, and are regarded as olfactory organs. Called also dorsal tentacles. See Illust. under Pygobranchia, and Opisthobranchia.

chemosensory (smell, taste) tentacles on the head or anterior section of the mantle.

paired sensory apparatus found on the head.