True about trematodes

Medically important member of the class Trematoda belongs to subclass Digenea, as they are digenetic, i.e., require two hosts. The definitive host in which they pass the sexual or adult stage are mammals, humans or animals, and the intermediate hosts in which they pass their asexual or larval stages are freshwater mollusks or snails. Trematodes are unsegmented and have no anus and body cavity.