The name given to marine polychaete worms (particularly to many species in the family Serpulidae) which construct permanent calcareous tubes on rocks, seaweeds, dock pilings, and ship bottoms. The individual tubes with hard walls of calcite-aragonite, ranging from 0.04 to 0.4 in. (1 mm to 1 cm) in diameter and from 0.16 to 4 in. (4 mm to 10 cm) in length, are firmly cemented to any hard substrate and to each other.