Answer :
The option which is an unsegmented acoelomate worm is flatworm. The correct answer is the first option. The other types of worms are all either segmented, or not considered to be acoelomate, which makes the first option the correct one, given that it falls under both of these categories.
The correct answer is option A, a. flatworm
Reason -
Phylum Platyhelminthes are phylums that are known as acoelomate species or animal as they do not have a coelom, or body cavity. Flatworms are also a type of Phylum Platyhelminthes which have an unsegmented and soft flattened body. Since these comes under both types of species categories i.e one with unregimented body and the other one with Acoelomate , thus option A seems to be a right choice
