Urechis unicinctus is a species of marine spoon worm found in the coastal waters of East Asia. This invertebrate is widely recognized by its distinctive appearance, leading to common nicknames like “fat innkeeper worm” and “penis fish.” While these names reflect its unique characteristics, the organism is a subject of biological study and culinary interest.
Habitat and Physical Characteristics
This marine spoon worm typically inhabits sandy or muddy seabeds in the Pacific Ocean, with a notable presence off the coasts of China, Korea, and Japan. It constructs U-shaped burrows within these soft sediments, which can extend several feet deep.
Urechis unicinctus has a cylindrical, unsegmented body, 10 to 30 centimeters (4 to 12 inches) long. It is generally yellowish-brown, and its skin features small papillae, giving it a textured surface. A spatula-shaped proboscis at its anterior end is used for burrowing and feeding.
Ecological Role and Behavior
The “fat innkeeper worm” moniker stems from its unique ecological role. Urechis unicinctus is a detritivore, meaning it consumes decaying organic matter and microscopic organisms found in the sediment. To feed, the worm secretes a ring of mucus from glands near its proboscis, attaching it to the burrow wall. As it moves backward, more mucus is extruded, forming a net that traps food particles suspended in the water.
The worm uses peristaltic contractions of its body to draw water through its burrow, filtering food through the mucus net. Once the net is filled with plankton, bacteria, and detritus, the worm moves forward and ingests the entire net. These burrows also provide shelter for other small marine creatures, such as crabs, shrimp, and gobies, which often reside within the worm’s dwelling, sometimes feeding on its discarded particles.
Culinary Significance
Urechis unicinctus holds culinary significance, particularly in East Asian cuisines. In Korea, it is known as “gaebul” (개불), often consumed raw as a delicacy. Prepared by cleaning and slicing, it is served fresh, sometimes still wriggling, and accompanied by dipping sauces like sesame oil with salt or a spicy gochujang and vinegar mixture. Its flavor is described as a blend of salty and sweet with a chewy texture, sometimes compared to clams or octopus.
Beyond Korea, it is also part of regional Chinese cuisine, especially in Shandong province. In China, it is commonly stir-fried with vegetables or dried and ground into a powder to enhance savory flavors. Its high protein content and amino acids contribute to its nutritional value.