Urechis unicinctus (traditional Chinese: 海腸; simplified Chinese: 海肠; pinyin: hǎicháng; Japanese: 螠虫; rōmaji: yumushi; Korean: 개불; romaja: gaebul) is a species of marine spoon worm. It is widely referred to as the fat innkeeper worm or the penis fish. The body is about 10–30 cm long, and the body is yellowish brown in color near the cylindrical shape of sausage. On the surface of the body there are many small papillae. There is a flat snout that can be clipped to the front of the mouth and can be seen as a head of another animal with a brain in the snout.
In the sand under the sea, U-shaped pipes are pitched and male and female are made in eggs and sperm, respectively. The eggs become adult through the Trocopora larvae. In Korea, it is eaten for food. It is used as bait for fishing such as flounder, sea bream. They are distributed in Korea, Japan, and the Pacific coast.
|Urechis unicinctus at a market in Korea.|
von Drasche, 1881
U. unicinctus, like other species of Urechis, lives in burrows in sand and mud. It gets the name "fat innkeeper worm" because the tunnels often contain other animals.
It is also used for fishing bait.