Pseudopotamilla reniformis and Perkinsiana rubra have irregular winding burrows, which penetrate to a distance of about 5 cm into hard limestone and are probably formed mostly by chemical means. Acid mucopolysaccharides are produced by parapodial glands and by the ventral gland shields, as in other sabellids. By producing tubes of such substances, which readily bind calcium, sabellids are pre-adapted for boring into calcareous substrata.