Urechis unicinctus, known as the fat innkeeper worm or (Chinese) penis fish,[2][3] 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.[3] 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.[4] 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.
^ abGong, J.; Zhao, R.; Deng, J.; Zhao, Y.; Zuo, J.; Huang, L.; Jing, M. (2018). "Genetic diversity and population structure of penis fish (Urechis unicinctus) based on mitochondrial and nuclear gene markers". Mitochondrial Dna. Part A, DNA Mapping, Sequencing, and Analysis. 29 (8): 1261–1268. doi:10.1080/24701394.2018.1444039. PMID29482423.