Pygidiopsis summa Onji and Nishio, 1916
This small trematode (0.3 to 0.5 mm long by about 0.2 mm wide) has been found in the small intestine of cats in Japan and Korea (Eom KS, Son SY, Lee JS, Rim HJ. 1984. Heterophyid trematodes (Heterophyopsiscontinua, Pygidiopsissumma and Heterophyesheterophyesnocens) from domestic cats in Korea. Korean J Parasitol 23:197-202.). It has also been reported from avian hosts. In Korea, human infections have been reported in a patient with a history of eating the flesh of raw, brackish-water fish (Seo BS, Hong ST, Chai JY. 1981. Studies on intestinal trematodes in Korea. III. Natural human infedftions of Pygidiopsissumma and Heterophyesheterophyesnocens. Seoul J Med 22:228-235.). Patients who were treated passed up to 4,000 of these trematodes after they were treated. The eggs are 18-20 µm by 9-11 µm.