Nū'cle-o-brănch, n.

n. [Lat. nucleus, nucleus, and branchiæ, gills.] (Zoöl.) One of a group of sea-snails having the foot flattened into a long fin, and usually a very small shell, called the nucleus, suspended from the back. They are very transparent, and are found far at sea, where they swim with their back downward. Woodward.