The life-cycle of Ergasilus sieboldi Nordmann (Copepoda: Poecilostomatoida), parasitic on British freshwater fish

The free-living stages in the life-cycle of Ergasilus sieboldi are described in detail. The life-cycle comprises six nauplius stages, five copepodid stages, and the adults. The naupliar dorsal organ is studied by scanning electron microscopy. This organ is retained in the first copepodid stage but lost in subsequent stages. The male maxilliped appears late in development, at copepodid V, and is fully functional after the final moult into the adult. The maxillipeds are missing in females.