Final answer:
The Eumetazoa includes all animals with true tissues and body symmetry, distinguished from Parazoa, which lack true tissues. They are further classified into radially or bilaterally symmetrical organisms, with bilateral ones often possessing a coelom and being categorized as either protostomes or deuterostomes.
Step-by-step explanation:
In contrast to the Parazoa, which includes organisms like sponges that do not have true tissues, the Eumetazoa includes all animals that have true tissues and body symmetry. The distinction between these two groups lies in the presence of specialized tissues derived from embryonic germ layers. Eumetazoa is divided into radially symmetrical and bilaterally symmetrical organisms.
Animals with bilateral symmetry usually have three germ layers (making them triploblasts) and may have an internal body cavity known as a coelom. This coelom can either be true or false (pseudo), forming the basis for the classification into coelomates and pseudocoelomates. Further subdivision is based on developmental patterns, namely protostomes and deuterostomes.