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Article: Crustaceans
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CopyrightCOPYRIGHT 2003 The Gale Group Inc. This material is published under license from the publisher through the Gale Group, Farmington Hills, Michigan. All inquiries regarding rights should be directed to the Gale Group. (Hide copyright information)
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Crustaceans
Crustaceans include crabs, lobsters, shrimp, krill, barnacles, and related species. There are approximately 40,000 crustacean species, the great majority of which are aquatic. Crustaceans are the only primarily aquatic group in the phylum Arthropoda, which also includes the insects and spiders. A few crustaceans, such as the familiar pillbug, have invaded terrestrial (land-based) habitats.
Like other arthropods, crustaceans are characterized by a segmented body, jointed appendages, and an external skeleton that offers protection from predators. The external skeleton, called a cuticle, is made of
chitin
. The cuticle is periodically molted in order to allow for growth. The ...