The Fat Innkeeper Worm is a common critter found in the sandy mud of the Elkhorn Slough. It lives in a U-shaped tunnel or burrow. It has a unique method of eating. It secretes a slime net, which serves to trap small food particles. The Worm circulates water through the tunnel, trapping food in the slime net. When the mucus net becomes loaded with food, it is loosened from its attachments and the entire net with its burden of food is swallowed by the worm.

At least four other animals are known to live with the Fat Innkeeper Worm in its tunnel home. That's how it got its name. Frequent guests of the Worm include a fish called a goby, a small pea crab, a clam and a scale worm. They feed on food that the Innkeeper Worm leaves behind.