|Urechis unicinctus at a market in Korea.|
Urechis unicinctus, known as the fat innkeeper worm or (Chinese) penis fish, is a species of marine spoon worm in East Asia. It is found in Bohai Gulf of China and off the Korean and Japanese coasts. It is not to be confused with a closely related species, Urechis caupo, which occurs on the western coast of North America and shares common names. The body is about 10–30 cm long, cylindrical in shape and yellowish-brown in color. On the surface of the body there are many small papillae.