The protostome developmental sequence arose just once in evolutionary history, resulting in two main subgroups—Lophotrochozoa and Ecdysozoa. What does this finding suggest? Select one: a. These two subgroups have a common ancestor that was a deuterostome. b. The protostomes are a polyphyletic group. c. Division of these two groups occurred after the protostome developmental sequence appeared. d. The lophotrochozoans are monophyletic.

c. Division of these two groups occurred after the protostome developmental sequence appeared.

Explanation:

Protosomes are such types of organisms in which the mouth part developed first during embryonic development. Those animals in which anus develop first are known as deuterostomes.  This differentiation takes place during the embryonic development of the organisms. Since lophotrochozoan and Ecdysozoa both are protostomes animals and categorized on the basis of molecular evidence. Thus these two groups were formed after the appearance of the protostomes.