The life cycle of Pygidiopsis ardeae Køie, 1990 (Digenea, Heterophyidae).

Ocellate cercariae, consistent with the description of Cercaria angularis Honer, 1961, developing in rediae in Hydrobia ulvae (Pennant) and Hydrobia ventrosa (Montagu) (Prosobranchia, Hydrobiidae) from Denmark, were shown to be larvae of Pygidiopsis ardeae Køie, 1990 (Heterophyidae, Pygidiopsinae). Euryhaline fishes such as the sticklebacks Gasterosteus aculeatus Linnaeus and Pungitius pungitius (Linnaeus), and the common goby Pomatoschistus microps (Krøyer) are second intermediate hosts in Danish inlets. These species and the flatfishes Platichthys flesus (Linnaeus) and Limanda limanda (Linnaeus) were laboratory infected. Cercariae penetrated the gills where some encysted, but most scattered throughout the body via efferent branchial arteries and the dorsal aorta to encyst mostly in the mesenteries, spleen, and on the surface of other viscera. Twelve-week-old (15 C) metacercariae fed to domestic chickens and pigeons developed to adults of P. ardeae in less than 4 days. Grey herons, Ardea cinerea Linnaeus, were naturally infected with P. ardeae, which was not found in gulls or cormorants from the same area and feeding on similar fishes.