One of the most fascinating creatures of the sea, these small but mighty jelly-bodied, shell-less mollusks are part of the sea slug family. Nudibranchs inhabit ocean waters throughout the world, from the Southern Ocean to the Arctic and everywhere in between. Depending on the species, adult sizes can range from 0.25 to 12 inches. These soft-bodied gastropods derive their name from the Latin word Nudibranchia, meaning naked gills, which is why most have feathery gills and horns on their backs. Learn about their ecology in this specialty program.