n 1  cap  :  a genus of tapeworms of the family Diphyllobothriidae that lack external evidence of segmentation, that as adults are usu. extremely short-lived internal parasites of fish-eating birds but include one (L. intestinalis) found rarely in humans, and that develop almost to maturity in the body cavity of freshwater fishes  2  :  a larval tapeworm developing reproductive organs and living in the body cavity of a fish .
 
 
 
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