nuchal organ
From ZooTerms (Dictionary of Invertebrate Zoology)
nuchal organ: 1. (Annelida: Polychaeta) A pair of ciliated sensory pits or slits in the head region.
2. (Arthropoda: Crustacea) In Branchiopoda, a sensory organ on the upper side of the cephalon.
3. (Sipuncula) Ciliated epidermal cells at the mid-dorsal edge of the oral disc; believed to be sensory.
