1. Lacking a backbone or spinal column; not vertebrate.
2. Of or relating to invertebrates: invertebrate zoology.
An animal, such as an insect or mollusk, that lacks a backbone or spinal column.
invertebrate , any animal lacking a backbone. The invertebrates include thetunicates and lancelets of phylum Chordata, as well as all animal phyla other than Chordata. The major invertebrate phyla include: the sponges (Porifera), coelenterates (Cnidaria), echinoderms (Echinodermata), flatworms (Platyhelminthes), roundworms (Nematoda), segmented worms (Annelida), mollusks (Mollusca), and arthropods (Arthropoda). Invertebrates are tremendously diverse, ranging from microscopic wormlike mezozoans (see Mezozoa) to very large animals such as the giantsquid. Approximately 95% of all the earthâ€™s animal species are invertebrates; of these the vast majority are insects and other arthropods. Invertebrates are important as parasites and are essential elements of all ecological communities