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Science & Nature • Marine Biology

Penis fish

“Penis fish” is a common nickname for *Urechis unicinctus*, a marine spoon worm found in East Asian coastal waters.

By Ethan Anderson| Reviewed by Olivia Bennett, Standards & Fact-Checking Lead| Updated July 26, 2026|2 min read| Fact-checked

“Penis fish” is a common nickname for *Urechis unicinctus*, a marine spoon worm found in East Asian coastal waters. Despite the name, it is not a fish but a worm in the family Urechidae, and it is also known as the fat innkeeper worm. It lives in burrows in sand and mud and is eaten in parts of East Asia.

Taxonomy and naming

*Urechis unicinctus* belongs to the family Urechidae and is commonly called the penis fish or fat innkeeper worm. The nickname refers to its appearance, but the animal is a marine worm rather than a true fish.

Distribution and habitat

The species is found in East Asian waters, including the Bohai Gulf of China and areas off the Korean and Hokkaido coasts. It lives in burrows that it makes in sand and mud.

Feeding and ecology

The worm is a detritivore that feeds on microscopic organic material. Its burrowing lifestyle is closely tied to soft seabed habitats.

Human use

In parts of Korea, China, and Japan, the species is eaten as a seafood delicacy. Its occasional mass wash-ups on beaches have also made it a subject of media attention.

Key facts

  • The name “penis fish” is a nickname, not a taxonomic name.
  • *Urechis unicinctus* is a marine spoon worm, not a fish.
  • It occurs in East Asian coastal waters, including China, Korea, and Japan.
  • The species lives in burrows in sand and mud.
  • It feeds on microscopic organic material and other detritus.
  • It is used as food in some East Asian cuisines.

Frequently asked questions

Is a penis fish actually a fish?
No. It is a marine spoon worm, not a fish.
What species is usually meant by “penis fish”?
The name usually refers to *Urechis unicinctus*.
Where does it live?
It lives in coastal marine sediments in East Asia, especially in sand and mud.
What does it eat?
It feeds on microscopic organic material and detritus.
Is it eaten by people?
Yes. It is consumed in some parts of Korea, China, and Japan.

References

  1. Wikipedia — https://en.wikipedia.org/wiki/Urechis_unicinctus
    Supports: Scientific name, common names, taxonomy, and distribution in East Asia.
  2. GBIF — https://www.gbif.org/en/species/2509002
    Supports: Common name usage for *Urechis unicinctus*.
  3. BBC News — https://www.bbc.com/news/world-us-canada-50779461
    Supports: Common name 'penis fish' for fat innkeeper worms and note that *Urechis unicinctus* is a delicacy in parts of East Asia.
  4. A-Z Animals — https://a-z-animals.com/animals/urechis-unicinctus-penis-fish/
    Supports: Habitat, feeding, burrowing behavior, and edible use in East Asia.
  5. Wikipedia — https://en.wikipedia.org/wiki/Urechidae
    Supports: Family Urechidae and relation to spoon worms.