I haven't seen a platyhelminth like that since I don't know when.

The answer is Phylum Ctenophora.

Phylum: Platyhelminth Inclusive of the tapeworm, and many others.

they are bilaterally symmetrical, their body has more than 2 cell layers and their body possesses 3 different sections; prosomium, trunk and a pygidium.

thanks for reading and i hope this helps you.:)

Schistosomiasis (also known as bilharzia, bilharziosis or snail fever) is a parasitic disease caused by several species of trematodes (platyhelminth infection, or "flukes"), a parasitic worm of the genus Schistosoma. Snails serve as the intermediary agent between mammalian hosts. Individuals within developing countries who cannot afford proper water and sanitation facilities are often exposed to contaminated water containing the infected snails.