: A tough, continuous outer layer called a syncytial tegument protects them from the host's digestive enzymes and immune system.

: They possess two muscular suckers—an oral sucker near the mouth and a ventral sucker (acetabulum) on the underside—to anchor themselves to host tissues.

Trematodes typically require at least two different hosts to complete their development:

Schistosomes and Other Trematodes - Medical Microbiology - NCBI

: Most are hermaphroditic (monoecious), containing both male and female reproductive systems and capable of self-fertilization. A notable exception is the Schistosoma genus, which has separate male and female sexes. Complex Life Cycle