October 29 - Megalodiscus temperatus

Megalodiscus temperatus is a digenean trematode belonging to the order Echinostomatiformes (Family Diplodiscidae). Diplodiscid flukes have a pair of posterior diverticula in the oral sucker, and the posterior sucker of these trematodes is about as wide as the greatest width of the body. Megalodiscus temperatus are common parasites of the rectum and urinary bladder of frogs. Eggs are shed from frog hosts, and miracidia hatch soon after the eggs reach the water. There is only one intermediate host for M. temperatus, snails of the genus Helisoma. Snails become infected when penetrated with miracidia, releasing cercariae into the water that subsequently encyst in the skin of frogs. Frogs regularly molt the outer layers of their skin, often ingesting the sloughed skin and the encysted metaceriae. Metacercariae excyst in the rectum, maturing in one to four months. Tadpoles can also become infected when ingesting cercaria. In this case, M. temperatus encysts in the stomach and excysts in the rectum of the tadpole. During metaphorphosis (tadpole intestines shorten considerably), M. temperatus migrates anteriorly then posteriorly again to the rectum.

Contributed by Jessica Light.