A marine worm (family Arenicolidae), up to 20 cm long, though some are longer, with a segmented body, feathery gills, and bristles along the sides of its middle segments. It lives in a U-shaped, mucus-lined burrow that it excavates in the seafloor sand in the intertidal zone, its digging producing casts that are a common sight on beaches at low tide. Lugworms occur throughout the coasts of north-western Europe.