Urechis unicinctus, commonly known as the innkeeper worm, inhabits muddy sands in coastal waters of East Asia. This sausage-shaped marine worm is notable for its U-shaped burrow, which also shelters other marine species. It feeds by filtering plankton and detritus, contributing significantly to the benthic ecosystem.

Urechis unicinctus is primarily native to the coastal regions of the northwest Pacific Ocean. Its geographical distribution includes countries such as China, Korea, and Japan. The species is particularly common along the Yellow Sea and the East China Sea, as well as the southern Sea of Japan.

Urechis unicinctus typically inhabits shallow intertidal and subtidal zones, often in muddy or sandy substrates. The environment is characterized by a temperate climate with moderate seasonal variations in temperature. These regions usually have high nutrient availability due to tidal movements.

Known as the innkeeper worm, Urechis unicinctus plays a crucial role in its ecosystem by aerating the sediment and facilitating nutrient cycling. Its burrows provide shelter for various commensal species, contributing to the biodiversity of the habitat. The species is adapted to live in low-oxygen environments and is an important food source for local marine predators.