Their epidermis is thickened to form a cuticle of syncitial arrangement, with the muscular layer above the cell bodies of the epidermis itself. The cuticle carries no associated cilia. Similarly absent is the gastro-intestinal tract, which has degenerated completely. Digestion occurs over the whole body surface of the animal, which compensates for its lack of a gut by living in the digestive tract of vertebrates where food is abundant. Furthermore, the ectoderm of tapeworms is covered with tiny microtrichia , dramatically increasing the surface area over which digestion can occur.
Most cestodes are very elongate and flattened, with some attaining staggering proportions.
There is generally a clearly defined head region bearing a complex organ of adhesion known as the scolex . The scolex has a variety of suckers and hooks that keep the parasite locked on to its host. Many tapeworms have a trunk divided into a succession of proglottids. The proglottid resembles a true, annelid segment, but is in fact merely a ring of weakness in the body wall. Each proglottid represents a reproductive structure containing both male and female gonads, which can be broken off from the body to regenerate asexually into a new tapeworm, or produce eggs sexually.