Invertebrates are animals that lack a vertebral column, or backbone, which evolved from the notochord. This group excludes all vertebrates in the subphylum Vertebrata. Notable invertebrate phyla include arthropods, mollusks, annelids, echinoderms, flatworms, cnidarians, and sponges. Invertebrates account for about 97% of all animal species and often have greater species diversity than vertebrates.
