The correct option is A Liver fluke
Liver fluke belongs to phylum Platyhelminthes. Platyhelminthes (liver-fluke) are first acoelomate animals which have organ system organization and bilateral symmetry. Jelly fish is a cnidarian animal. It is acoelomate. Roundworm belongs to phylum Aschelminthes and is a pseudocoelomate animal. Crab belongs to phylum Arthropoda and is bilaterally symmetrical coelomate animal. Thus, the correct answer is option A.