False-color light micrograph of the scolex (head) of the adult pork tapeworm, Taenia solium magnified 12 times. The image shows the hooks and four suckers with which the tapeworm attaches itself to the intestinal walls of its host. Humans are the principal host of this tapeworm, which annually infects some 4 million people worldwide.
The tapeworm is a member of a group of intestinal parasites, so named because it is long and flat. Tapeworms absorb their host's digested food directly through their entire surface area; they have no digestive system of their own.
Tapeworms form the class Cestoda of the flatworm phylum Platyhelminthes. A scolex, or head, only 1.5–2 mm (about 0.06 in) in diameter, is attached to the gut and behind this the body consists of a ribbon of identical flat segments, or proglottids, each containing reproductive organs. These proglottids are budded off from behind the scolex. Mature proglottids containing eggs pass out with the feces where larval stages can infect intermediate hosts.