Euryhelmis monorchis Ameel, 1938
This trematode parasite (Eury = wide and helmis = worm along with monorchis = single testis) is a parasite of mink in North America. The worm tends to be wider (0.6 mm) than long (0.4 mm). It resembles the parasite, Euryhelmis squamula of the European polecat, Putorius putorius. The life cycle involves a fresh-water snail, Pomatiopsis lapidaria, along with frogs, Rana clamatans, Rana pipiens, and Rana palustris as the second host (Ameel DJ. 1938. The morphology and life cycle of Euryhelmismonorchis n. sp. (Trematoda) from the mink. J Parasitol 24:219-224). A cat was experimentally infected with this parasite by feeding it metacercariae, and cats could perhaps become naturally infected. The eggs are operculate, undeveloped when laid, and measure 29 µm by 14 µm.
Figure 2-19.Euryhelmismonorchis from an experimentally infected white rat. THe large single dark testis can be observed on the right side of this specimen.