Final answer:
Tapeworms are cestodes that belong to the phylum Platyhelminthes. They are specialized parasitic flatworms that live in the digestive tracts of vertebrates and have a body structure segmented into proglottids, lacking their own digestive system.
Step-by-step explanation:
Tapeworms, known scientifically as cestodes, are a specialized form of flatworms belonging to the phylum Platyhelminthes. This group also includes other parasites like flukes, as well as free-living forms such as turbellarians. Tapeworms are known for their parasitic lifestyle inside the digestive systems of vertebrates, including humans. They do not have a digestive system of their own; instead, they absorb nutrients directly from the host's intestine.
Tapeworms have a distinctive body structure consisting of a series of segments called proglottids, each containing male and female reproductive organs. These proglottids detach when gametes are fertilized, releasing eggs into the environment. The lifecycle of a tapeworm may involve multiple hosts – the eggs are consumed by an intermediate host and eventually form cysticerci, which are then consumed by the definitive host, where the tapeworm matures in the digestive tract.
The final answer to the student's question is that tapeworms belong to phylum Platyhelminthes. This is consistent with the characteristic features of tapeworms, such as their flat body shape, absence of a digestive system, and parasitic mode of living.