Three genera ("Aspidosiphon", "Lithacrosiphon" and "Cloeosiphon") in the Aspidosiphonidae family possess epidermal structures, known as anal and caudal shields. These are patches of thickened, hard plates, and are used for boring into rock; the anal shield is near the anteriorly-located anus on the trunk, just below the introvert of the animal, while the caudal shield is at the posterior of the body. In "Aspidosiphon" and "Lithacrosiphon" the anal shield is restricted to the dorsal side, causing the introvert to emerge at an angle, whereas it surrounds the anterior trunk in "Cloeosiphon" with the introvert emerging from its center. In "Aspidosiphon" the shield is a hardened, horny structure; in "Lithacrosiphon" it is a calcareous cone; in "Cloeosiphon" it is composed of separate plates. When the introvert is retracted in these animals, the anal shield blocks the entrance to its burrow. At the posterior end of the trunk, a hardened caudal shield is sometimes present in "Aspidosiphon"; this may help with anchoring the animal in its burrow or may be used in the boring process.