invertebrate

Animal without a backbone. The invertebrates form all of the major divisions of the animal kingdom called phyla, with the exception of vertebrates. Invertebrates include the sponges, coelenterates, flatworms, nematodes, annelids, arthropods, molluscs, and echinoderms.

Primitive aquatic chordates such as sea squirts and lancelets, which only have notochords and do not possess a vertebral column of cartilage or bone, are sometimes called invertebrate chordates, but this is misleading, since the notochord is the precursor of the backbone in advanced chordates.