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In biology, the Cestoda is the class of tapeworms, parasitic flatworms that live as adults in the digestive tracts of vertebrates. They have a round head called a "scolex" with hooks and suckers for attachment. Posterior to scolex, they have proglottid s (immature, mature, gravid) that contain numerous eggs. The proglottid is the sac of sex organs. Not having defined digestive tract, they absorb food predigested by the host.

Mature proglottids are released from the mature tapeworm and leave the host in its feces. For example, human feces contaminate the food of intermediate host, such as pigs or cattle, and the tapeworm eggs develop into larvae ( cysticercus ). Humans can get larvae of tapeworms by eating uncooked meat. This tapeworm is often referred to as a "bladderworm." It is shaped thin like a strip of tape unlike the rounded earthworm. The large tapeworms can be 20m or longer and they can be harmful to humans.

There are two subclasses in class Cestoda, the Cestodaria and the Eucestoda . All the animals we usually think of as tapeworms are in Eucestoda; only a few species of unusual worms are in subclass Cestodaria.

Reference

• Campbell, Reece, and Mitchell, Biology, 1999