ON THE MORPHOLOGY AND LIFE CYCLE OF THE TREMATODE TANAISIA ZARUDNYI (SKRJABIN, 1924) BYRD AND DENTON, 1950, FROM THE RUFFED GROUSE, BONASA UMBELLUS L.
Tanaisia zarudnyi occurs in the ureters and kidney tubules of ruffed grouse from Ontario and Michigan. The dark brown, operculate eggs are fully developed when oviposited. They remain viable for long periods of time at 2 to −15 °C and can withstand a temperature of −49 °C for 1 to 2 days. They hatch only when ingested by some mollusc. Development occurs in the digestive gland of the terrestrial snails Anguispira alternata and Succinea ovalis. Daughter sporocysts complete development in 6 weeks, by which time they contain undeveloped cercarial bodies. Within the next 2 weeks, most of the distomate. brevicercous cercariae are fully developed. The cercariae encyst within the daughter sporocyst, utilizing the contents of subcuticular glands to form the cyst. Encysted metacercariae are killed in the gizzard when fed to chickens, but excyst when inoculated directly into the duodenum. Excystation apparently results from secretions of the anterior glands of the stimulated metacercaria rather than from digestion of the cyst wall by the host. A 6-week-old ruffed grouse became infected when fed metacercariae, but 9 older ruffed grouse, 17 chickens, 4 white-throated sparrows, and 6 pheasants, fed similarly, were not infected. Apparently there is both host and age resistance to infection with this parasite.