Which phylum of animals lacks organ systems?

Platyhelminthes represents an example of

During its life cycle,$Fasciola$ $hepatica$ $(Liver$ $Fluke)$ infects its intermediate host and primary host at the following larval stages respectively:

Given below are two statements.
Statement $I$: Cephalic ganglion appears like $U$ shaped structure in Hydra.
Statement $II$: Ventral nerve cords are connected to each other by commissure in a ladder like manner in Planarian.
In the light of above statements,choose the most appropriate answer from the options given below:

. . . . . . is an example of a trematode parasite.

Members of class $Trematoda$ are commonly called as