Khawia japonensis, a tapeworm, was described from Japan, and found in Common Carp (Cyprinus carpio) in Japan, eastern Russia, China, Vietnam, and Italy. It was re-described as Khawia iowensis (Calentine and Ulmer 1961), from intestines of Common Carp, introduced in the Iowa River drainage, Iowa. Subsequently, this tapeworm was found in Wisconsin, Oklahoma and North Dakota. It was also collected from carp in Lake Erie . It was collected in Common Carp, in a survey of fish parasites at the Tracy Pumping Plant, in the Sacramento-San Joaquin Delta in 1972-73. The eggs of tapeworms are deposited with the fishes' feces, and hatch into a larval form known as an oncosphere. Oligochaetes can serve as an intermediate host, ingesting the eggs and larvae.