invertebrate

invertebrate ĭn˝vûr´təbrət, –brāt˝ [key], any animal lacking a backbone. The invertebrates include thetunicatesandlanceletsof 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 (seeMezozoa) to very large animals such as the giantsquid. Approximately 95% of all the earth's animal species are invertebrates; of these the vast majority areinsectsand other arthropods. Invertebrates are important as parasites and are essential elements of all ecological communities.

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).

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