Flipper (anatomy)

thumb|350px|"Lampanyctodes hectoris" ">
(1) - operculum (gill cover), (2) - lateral line, (3) - dorsal fin, (4) - fat fin, (5) - caudal peduncle, (6) - caudal fin, (7) - anal fin, (8) - photophores, (9) - pelvic fins (paired), (10) - pectoral fins (paired)

A flipper is typically flat limb evolved for movement through water. Various creatures have evolved flippers, for example most fish (although for fish the usual term is fin), as well as certain mammals (cetaceans, pinnipeds), reptiles (turtles, and the now extinct plesiosaurs, mosasaurs, ichthyosaurs, and metriorhynchids), and birds (penguins).

Flippers sometimes occur in non-flippered species as the result of a birth defect. For example, the morning-sickness drug thalidomide caused some infants to be born with flipper-like limbs.