The parasitic larva of certain freshwater mussels of the family Unionidae,having hooks for attaching to the gills or other external parts of a host fish.

• 瓣钩幼虫珠蚌科淡水贝类的寄生幼体，长有钩并用来附着在寄宿主鱼的鳃或其他体外部分。