Any of various aquatic insects and crustaceans having limbs that are oar-shaped and adapted for swimming. Now: specifically any of several small primitive crustaceans constituting the class Remipedia, which are found in marine caves and have wormlike segmented bodies, each segment bearing a pair of biramous swimming limbs.

Originally known only as a fossil, the first living members of the Remipedia were discovered in 1979.

Of an aquatic insect or crustacean: having limbs that are oar-shaped and adapted for swimming. Now: specifically of or relating to the class Remipedia of crustaceans.