invertebrate ĭn˝vûr´təbrət, –brāt˝ [key]
, any animal lacking a backbone. The invertebrates include the tunicates
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.
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).
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.
See more Encyclopedia articles on: Zoology: Invertebrates