Sand masons grow to 15 centimeters long. They live in self-made tubes from sand and shell grit with a frayed opening. The worm itself is yellowish, pink or brown with red gills. It sticks its head with its long white tentacles out of the tube to catch food particles in the water. When sensing danger, the worm retracts into the tube. Sand masons are commonly found on sandy parts of the tidal marshes and the bottom of the North Sea.