nuchal constriction (MOLL: Cephalopoda) In most Sepiidae and Teuthoidea and a few Octopodidae, the separation or constriction between the head and body or neck.
nuchal organ(s) 1. (ANN: Polychaeta) A pair of ciliated sensory pits or slits in the head region. 2. (ARTHRO: Crustacea) In Branchiopoda, a sensory organ on the upper side of the cephalon. 3. (SIPUN) Ciliated epidermal cells at the mid-
dorsal edge of the oral disc; believed to be sensory.
nuchal papilla (ANN: Polychaeta) Small sensory papilla at the base of the prostomium; cirrus.
nuchal tentacles (platy: Turbellaria) In Polycladida, tentacles well set back from the anterior part of the body.
nuclear envelope Double layered membrane separating the nucleoplasm from the cytoplasm; nuclear membrane.
nuclear plate A metaphase or equitorial plate.
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