Platyhelminthes, or flatworms, eat worms and other animals that are smaller than they are, including single-celled animals and tiny mollusks. Some flatworms are cannibalistic. They also eat bacteria and algae.
Flatworms eat debris and the tissues of dead or injured animals. They find their food through sensors that function like antennae. Flatworms at least partially digest their prey externally before eating it or sucking the fluids from it.
Many platyhelminthes, such as nematodes, roundworms and tapeworms, are parasitic. They can live in both humans and animals. One common type of parasitic roundworm causes trichinosis. The host contracts this disease by eating undercooked meat that harbors the larvae of the trichinella worm. The larvae mature in the intestine, then produce larvae of their own. These larvae migrate throughout the body and eat the host's blood cells. They cause symptoms such as abdominal cramps, diarrhea and fatigue in the early stages. Fever, myalgia and headache occur after the larvae have traveled from the intestine and burrowed into other organs.
Tapeworms live in the intestine of its host. Unlike other platyhelminthes, this flatworm has neither a mouth nor a digestive tract. It absorbs nutrients in the host's gut through its skin. Some flatworms parasitize plants, including soybeans, potatoes and pine bark.