“Spaghetti worm” is the common name for several species of polychaete* worms that live in sand or mud tubes in the intertidal zone. They are members of the family group called Terebellidae characterized by having movable tentacles in the head area that are not withdrawn into the mouth. The white, string-like tentacles can be extended many times the body length over the surface of the sediment searching for particles of food.
They usually form their tubes under or nestled against rocks or other large objects including shellfish. Entirely marine, they are commonly seen on marina floats or burrowed in beach sediments.
*pronounced like “polly-keet”