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one of the larval stages in the development of tapeworms (the broad fish tapeworm, Liguld). The body measures 2–80 cm long and is unsegmented. A fish (the second intermediate host of tapeworms) swallows a copepod (the first intermediate host) containing a larva—the procercoid. The larva penetrates the wall of the fish’s intestine to the body cavity, where it is converted to a plerocercoid. If the definitive host (a man, dog, or cat for the broad fish tapeworm; aquatic birds for Liguld) eats the affected fish, the plerocercoid is transformed into an adult worm in the new host’s intestine.