Question: why are flatworms more complex than cnidarians?
Answer: Flatworms are more complex than cnidarians. Cnidarians have two layers of cells, the ectoderm and the endoderm; flatworms have a middle layer called the mesoderm between the other two layers (Fig. 3.16). ... The cells of the ectoderm and endoderm are also more organized than similar cells of cnidarians.