The protostome developmental sequence arose just once in evolutionary history, resulting in two main subgroups-Lophotrochozoa and Ecdysozoa. What does this finding suggest?
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.

Question

Quizplus · Accepted Answer

The fact that the protostome developmental sequence arose just once suggests that the division of Lophotrochozoa and Ecdysozoa occurred after the protostome developmental sequence appeared. Therefore, choice C is the correct answer as it reflects this suggestion.

Note: Choice A is incorrect because the two subgroups cannot have a common ancestor that was a deuterostome if they both arose from the protostome developmental sequence. Choice B is incorrect because the protostomes are a monophyletic group, arising from a single common ancestor. Choice D is incorrect because the monophyly of the lophotrochozoans is not implied by the fact that the protostome developmental sequence arose just once.

The Protostome Developmental Sequence Arose Just Once in Evolutionary History