Salmacina species (Huxley, 1855) or Filograna implexa Berkeley, 1835
Coral worm species or Sagebrush tube worm (Salmacina species)
Probably a Salmacina species, because the specimens in the photo's seem to lack an operculum. Filograna has an operculum.
Bagur - El Furio Fito de Bagur, Costa Brava, Spain, 1-6-2015.
Bagur - El Furio Fito de Bagur, Costa Brava, Spain, 1-6-2015.