What are animals without backbones called?

Invertebrates are animals that neither develop nor retain a vertebral column, which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordate subphylum Vertebrata, i.e. vertebrates. Nonetheless, almost all invertebrates belong to the monophyletic clade Protostomia, including arthropods, molluscs, annelids, and flatworms. Some of the well-known remaining invertebrates are deuterostomes such as echinoderms and tunicates, or animals outside the protostome/deuterostome split, including cnidarians and sponges.