Question

Which statement best describes how these animals are grouped?

A
sponges, cnidarians, flatworms, roundworms
B
annelids, arthropods, mollusks, echinoderms


A. by body symmetry
B. by the presence of a true coelom
C. by early development of the blastopore D.by existence of germ layers

Answer 1

Sponged and cnidarians, flatworms and roundworms are considered primitive and have no coelom at all and are called acoelomates. Their three germ layers are packed together with no body cavity except the digestive cavity. So Group A would be classified by B, true coeloms.

Annelids, Arthropods, mollusks, and echinoderms are arthopods are either protosome colelomates or deutrostome coelomates. They are all invertebrates and classifed by body symmetry. Annelids have segmented body structure; arthopods have segmented head,thorax, and abdomen; mollusks have head-foot, visceral mass, and mantle sections; and echinoderms possess segmented claw-like limbs (cirri)

Answer 2

Group B classfied by A.