Correct Option: A

Acoelomates are animals that have no body cavity or coelom. The examples are poriferans, coelentrates, ctenophores, platyhelminthes and nemertean. Pseudocoelomates are animals that have false or pseudo coelom. Examples are aschelminthes. Coelomates are animals that has true coelom enclosed by mesoderm on both sides. Examples: from annelida to arthropoda are coelomates. Hence roundworms are pseudocoelomates, molluses and insects are coelomates while flatworms are acoelomates.