The Little Red Sausage of the Beach - The Innkeeper Worm
Most people are likely unfamiliar with the "innkeeper worm" (Ochetostoma erythrogrammon), as not only is its name hard to pronounce, few people have seen its "true form". Some say it looks like a sausage, while others say it looks like mucus. While these descriptions are very different, both are actually accurate, as they describe different parts of the worm’s body. The innkeeper worm is a marine creature widely scattered locally, often inhabiting sheltered sandy shores. It is time that everyone learns more about it!
The innkeeper worm belongs to the Echiura, a group of marine animals. Globally, there are about 150 known species of Echiurans, most of which live in shallow sea sand or mud, rock crevices, or burrow in coral reefs and shells. There are innkeeper worms scattered all over Hong Kong. During low tide, if you visit some sheltered sandy shores, such as Ting Kok, Hoi Ha Wan, and Shui Hau, you may be able to spot them.
The innkeeper worm's body is divided into two parts: the trunk and the proboscis. The trunk has longitudinal stripes of red and light pink, and the red colouration is due to the presence of a substance similar to haemoglobin in its body fluids, which allows it to transport more oxygen in the oxygen-deprived environment under the sand and mud. Due to its red colour and cylindrical, plump, and rounded shape, it resembles a little red sausage!
The Hidden Little Red Sausage
Don't assume that this little red sausage on the beach must be so eye-catching that it can be easily found! In fact, the innkeeper worm often buries its trunk in burrows in the sand and mud, only extending its proboscis, and the proboscis is translucent milky white. As soon as it senses any movement around, it quickly retracts into the sand, so it is not easy to observe them.
The colour and shape of its proboscis are like mucus! The innkeeper worm feeds on sediments, using the sticky surface of its proboscis to stick food particles onto the mouth canal as it extends to shore, and then using cilia to transport them into its mouth. Its proboscis is also extremely retractable and is able to extend up to ten times its body length, making it easier to search for food.
The Hospitable Innkeeper
In addition to sheltered sandy shores, innkeeper worms also inhabit areas under rocks or in coral sand beds within coral reef areas. They will construct U-shaped or L-shaped burrows as shelter. Their name "innkeeper", describes their burrowing nature.
Since they are called "innkeepers", they are naturally very "hospitable". Other crustaceans or bivalves are often found near the burrows of the innkeeper worms. Foreign studies have discovered two types of crabs and one type of bivalve in their burrows, and the studies suggest that they may have a symbiotic relationship with innkeeper worms.
Beyond their "hospitality", innkeeper worms are also very important to the ecosystem. As they feed on sediments, they play an important role in the turnover and nutrient cycling of marine sediments, which contribute towards maintaining the health and balance of the marine ecosystem.