Final answer:
Eumetazoa are classified into two main categories based on body symmetry: radial and bilateral. Bilaterally symmetrical animals are characterized by having three germ layers (triploblasts) and may possess a coelom, which is further classified into protostomes and deuterostomes. The correct option is 1.
Step-by-step explanation:
Eumetazoa are classified on the basis of body symmetry into radial symmetry and bilateral symmetry. Radial symmetry is found in non-motile or simpler organisms like cnidarians and ctenophores, while bilateral symmetry facilitates active movement and is seen in more complex organisms that are part of the Bilateria clade.
Additionally, animals with bilateral symmetry are generally characterized by the development of a third embryologic germ layer, known as the mesoderm, leading to a triploblastic condition.
Eumetazoa with three germ layers, called triploblasts, are further classified by the presence or absence of an internal body cavity or coelom. True coelomates have a body cavity completely lined with mesoderm, while pseudocoelomates have a body cavity that is only partially lined with mesoderm. Coelomates are divided into two groups, protostomes and deuterostomes, based on developmental characteristics such as patterns of cleavage and coelom formation.
In conclusion, the Eumetazoa can be grouped into radially symmetrical and bilaterally symmetrical organisms, focusing on their body plans and further subdivided based on the complexity of their tissue layers and body cavity structure.