The edges of the mantle may extend far beyond the main part of the body , forming flaps , double-layered structures adapted for many different uses , including for example , the siphon . This anatomical structure in molluscs often resembles a cloak because in many groups the edges of the mantle extend far beyond the main part of the body , forming flaps , double-layered structures which have been adapted for many different uses , including for example , the siphon .