Commonly referred to as the tapeworm they have a flat body. There is an anterior region called scolex. The scolex contains four suckers. The main sucker is leaf-like. Behind the scolex is a third part the strobila. An anterior nerve mass lies in the scolex. They generally long, some reach 40 ft (12 m). They have a complex body. The muscles layer of tapeworms consist of the same circular and longitudinal layers but in addition there is a secondary parenchymal musculature of longitudinal transverse and dorsoventral fibers which encloses the interior parenchyma. Contains reproductive units called proglottids. A complete reproductive system occurs within each proglottid. Cross fertilization occurs with adjacent individuals in the host also self-fertilization between two different proglottid.