Serpula vermicularis is a slender, tube-dwelling polychaete between 5 and 7 cm in length with about 200 segments. The tubes are cylindrical with occasional rings and irregular lengthwise ridges cut into blunt teeth. The operculum is calcareous and funnel shaped with radial grooves and a serrated circumference. The colour of the body of the worm varies from pale yellow to brick red. The tube is pinkish-white and the operculum is patterned with red and white rays.The tube is attached to hard substrata at the base but in reef aggregations is often free for much of its length.