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There are over 3000 types of Nudibranch (pronounced nu-da-brank) means "naked gill," an apt name because their gills are external. Many nudibranchs have bright color patterns, which warn predators to keep away. Several nudibranchs have glands along the bottom of the mantle that store the poisonous chemicals derived from their food, and by associating bright color with bad tastes, predators may leave them alone. Source: National Geographic.
All the photos were taken by Alex Suh.