invertebrate

invertebrate , any animal lacking a backbone. The invertebrates include the tunicates 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 giant squid . Approximately 95% of all the earth'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.

Bibliography: See A. Kaestner, Invertebrate Zoology (3 vol., 1967-70); R. D. Barnes, Invertebrate Zoology (5th ed. 1987); R. Buchsbaum et al., Animals without Backbones (3d ed. 1987).

invertebrate Any animal that lacks a vertebral column (backbone). Invertebrates include all nonchordate animals as well as the more primitive chordates (see Chordata).

invertebrate An animal without a backbone; invertebrates make up about 95% of all animal species and are found in every available habitat on Earth.