The excretion of metabolic wastes in Arenicola marina (Lugworm) occurs through the use of nephridia, long coiled tubes lined with cilia on their internal surface. During this process, blood and coelomic fluids enter the nephridia as nutrients, water, and salts are released before the left over wastes are released through the nephridiopore. In Arenicola marina only body segments four to nine contain nephridia because in sedentary Polychaetes the number of nephridia is often less than that of other members of the Annelida phylum.