Concept:Invertebrates are animals without a backbone; chordates are the group that includes animals with backbones.Explanation:Flat worms, round worms, and protozoans do not have backbones, so they are invertebrates.Chordates, however, are animals with a notochord and include vertebrates, which have backbones.Therefore, the animal that is not invertebrate is chordate.Answer:C. chordate