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Invertebrates

Invertebrates

Invertebrates are animals without backbones. This simple definition hides the tremendous diversity found within this group which includes protozoa (single-celled animals), corals, sponges, sea urchins, starfish, sand dollars, worms, snails, clams, spiders, crabs, and insects. In fact, more than 98 percent of the nearly two million described species are invertebrates. They range in size from less than one millimeter to several meters long. Invertebrates display a fascinating diversity of body forms, means of locomotion, and feeding habits.

Invertebrates are ectotherms (cold-blooded): they warm their bodies by absorbing heat from their surroundings. Most invertebrates live in water or spend at least some part of their life in water. The external layers of aquatic invertebrates are generally thin and permeable to water. This structure allows the ready exchange of gases needed to keep the animal alive. Some aquatic vertebrates do have specialized respiratory (breathing) structures on their body surface. Aquatic invertebrates feed by ingesting their prey directly, by filter feeding, or by actively capturing prey.

Some groups of invertebrates live on land. Common examples include the earthworms, insects, and spiders. These invertebrates need to have special structures to deal with life on land. For example, earthworms have strong muscles for crawling and burrowing and, since drying out on land is a problem for them, they secrete mucous to keep their bodies moist. Insects and spiders move by means of several pairs of legs and are waterproof.

[See also Arachnids; Arthropods; Butterflies; Cockroaches; Corals; Crustaceans; Insects; Mollusks; Protozoa ]

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invertebrate

invertebrate (Ĭn´vûr´təbrət, –brāt´), 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.

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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"invertebrate." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. 21 Aug. 2017 <http://www.encyclopedia.com>.

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invertebrate

in·ver·te·brate / inˈvərtəbrit; -ˌbrāt/ • n. an animal lacking a backbone, such as an arthropod, mollusk, annelid, coelenterate, etc. The invertebrates constitute an artificial division of the animal kingdom, comprising 95 percent of animal species and about 30 different phyla. Compare with vertebrate. • adj. of, relating to, or belonging to this division of animals. ∎ humorous irresolute; spineless: so invertebrate is today's Congress regarding foreign policy responsibilities.

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"invertebrate." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. 21 Aug. 2017 <http://www.encyclopedia.com>.

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invertebrate

invertebrate Term for an animal without a backbone. There are more than one million species of invertebrates, divided into 30 major groups. One of these is Arthropoda (joint-legged animals), the largest of all animal phyla in terms of numbers of species. Most are insects, but it also includes crustaceans and arachnids. Molluscs make up the second largest group of invertebrates. See also arthropod; crustacean; phylum

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"invertebrate." World Encyclopedia. . Encyclopedia.com. 21 Aug. 2017 <http://www.encyclopedia.com>.

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"invertebrate." World Encyclopedia. . Retrieved August 21, 2017 from Encyclopedia.com: http://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/invertebrate

invertebrate

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

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"invertebrate." A Dictionary of Biology. . Encyclopedia.com. 21 Aug. 2017 <http://www.encyclopedia.com>.

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invertebrate

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

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"invertebrate." A Dictionary of Earth Sciences. . Encyclopedia.com. 21 Aug. 2017 <http://www.encyclopedia.com>.

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"invertebrate." A Dictionary of Earth Sciences. . Retrieved August 21, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/invertebrate