Urechis unicinctus (simplified Chinese: 海肠; traditional Chinese: 海腸; pinyin: hǎicháng; Japanese: 螠虫 or ユムシ yumushi; Hangul: 개불; RR: gaebul) is a species of marine spoon worm. It is widely referred to as the fat innkeeper worm or the penis fish.
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.
In Chinese cuisine the worm is stir-fried with vegetables, or dried and powdered to be used as an umami enhancer. In particular, the worm is considered an important ingredient in Shandong cuisine and is used in numerous recipes.
It is also used for fishing bait.