The distribution and life cycle of a dicrocoeliid trematode, Brachylecithum orfi Kingston and Freeman, 1959, from the biliary ducts of the ruffed grouse, Bonasa umbellus, in Ontario and Michigan, have been studied in the definitive host and the intermediate molluscan hosts. Oval, dark brown, operculate eggs contain fully developed miracidia at oviposition. The eggs are coated with a lipid which prevents uptake of water and hatching until they are eaten by a mollusc; they will survive for more than 3 years at 2 °C and will tolerate exposure to −49 °C. The eggs hatch and larval stages develop in Zonitoides arboreus, Z. nitidus, Cionella lubrica, Deroceras laeve, and D. reticulatum, but not in 13 other species of terrestrial molluscs. Small, rounded, daughter sporocysts develop within the saclike mother sporocysts during the first 30 days after ingestion of eggs by suitable molluscs. Daughter sporocyst and cercarial development is completed 89–278 days after infection, depending on the species of mollusc and the temperature. The cercariae escape from the sporocyst endosac through a birth canal into the sinusoidal spaces of the mollusc. They migrate to the lung and out onto the dorsum of the mollusc via the respiratory pore, where they aggregate in numbers in slimeballs that are deposited on the substratum. Cercarial production continues for more than 100 days after onset. The longicercous, mesostomate xiphidiocercariae have a flame cell formula of 2((2 + 2 + 2) + (2 + 2 + 2)); they are provided with 6 preacetabular and 12 postacetabular glands, both groups of which open through pores lateral to the shank of the cercarial stylet. Cercariae in slime masses survive for 48 hours. When exposed to larval Colorado potato beetles, larval willow chrsyomelids, and mound-building ants, the cercariae penetrated the gut wall and encysted in the haemocoel, but died shortly afterwards.
LARVAL STAGES OF PHYLLODISTOMUM SP. (DIGENEA, GORGODERIDAE) FROM THE DUCK MUSSELS ANODONTA ANATINA IN UKRAINE
