Answer
The Cnidarians share a number of features with other animals which the sponges lack, making them clearly more closely related to the other animals than the sponges are. These features include: True tissues, embryos with germ layers, developmentally-defined symmetry, and Hox genes.
Work Step by Step
Skim p. 676 and make a list of differences between sponges and cnidarians, then skim the list to see which are shared by all animals other than sponges.
