Urechis unicinctus, also commonly known as the Chinese penis fish, or fat innkeeper worm, is a type of marine spoon worm you probably haven’t heard about.
It is not accessible in other parts of the world as it is found primarily off the Korean and Japanese coasts and in the Bohai Gulf of China.
Though often mistaken for Urechis caupo, which can be found on the western coast of North America and shares common names, the Chinese penis fish is a different species altogether.
The body of this uncommon aquatic animal is about 10–30 cm in length, has a cylindrical shape, and yellowish-brown skin color. One prominent feature of this spoon worm is the many small papillae on the surface of its body.
Males and females of the Chinese penis fish, respectively, produce sperm and eggs.
Scientific classification
- Kingdom: Animalia
- Phylum: Annelida
- Class: Polychaeta
- Subclass: Echiura
- Family: Urechidae
- Genus: Urechis
- Species: U. unicinctus
- Binomial name: Urechis unicinctus
Ecology of the Chinese penis fish
This spoon worm, often mistaken for a fish because of its misleading name, is a detritivore.
The Chinese penis fish feeds on detritus, and is known to behave like other species of Urechis, living and burrowing in mud and sand.
These spoon worms are known to make a U-shaped burrow in the soft sediment of the seabed.
They have a ring of glands at the front of their proboscis, which secretes a kind of mucus that sticks to the wall of the burrow.
The worm keeps on exuding it’s unique mucus as it moves in backward motion in the burrow are creates a mucus net.
To gather its food, this spoon worm draws water through its burrow using peristaltic contractions of its flexible and soft body. During this process, food particles get stuck to the mucus net the worm had created.
When the Chinese penis fish has gathered enough food in its mucous net, it moves in a forward motion in its burrow and swallows both the net it created and the entangled food.
This process is repeated for as many times as possible. And for Chinese penis fish living in an area with lots of detritus are available, the entire process may be completed in just a few minutes.
Uses of the Chinese penis fish
In Korea and some other Asian countries, these spoon worms are eaten as food, often uncooked with sesame oil or gochujang and salt. They are distributed in Japan, Korea, and the Pacific coast.
In Chinese cuisine, the spoon worms are stir-fried with vegetables and eaten as a main or side dish. They can also be dried and ground to powder to be used later as an umami enhancer.
Another widespread use of Chinese penis fish is as fishing bait for fish like flounder and sea bream.
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