most highly specialized of flatworms are members of Cestoidea
2 unique adaptations to a parasitic lifestyle characteristic of a tapeworm: they lack a mouth and digestive tract in all of its life cycle stages; absorb nutrients directly across their body wall. Most adults consist of a long series of repeating units called proglottids.
not complex because the environment of the digestive tract is stable and doesn't require the development of adaptations
About 3,500 species
Examples in Humans: Beef Tapeworm (Taeniarhynchus saginatus), Pork Tapeworm (Taenia solium), Broad Fish Tapeworm (Diphyllobothrium latum)
Taken From:
http://www.portalsaofrancisco.com.br/alfa/filo-platelmintos/imagens/cestoda-2.jpg
Subclass Cestodaria
General Characteristics
body not subdivided into proglottids
larva in crustaceans
adult in fishes
all endoparasites in the intestine and coelom of primitive fishes
no digestive tract
dioecious
suckers
About 15 species
Example: Amphilina, Gyrocotyle
Subclass Eucestoda
General Characteristics
"True Tapeworms"
body divided into scolex, neck, and strobila
Scolex- have suckers; sometimes have a rostellum of hooks
strobila composed of many proglottids
monoecious; both male and female reproductive systems in each proglottid