Crustaceans are one of four basic groups of arthropods (the other three being the myripods, arachnids and insects). The group includes crabs, lobsters, shrimp, krill, crayfishes, wood lice and barnacles.
Crustaceans are by no means as diverse in species number as the insects or even the arachnids, but they do come in a mind-boggling array of shapes and sizes. Since crustaceans are with few exceptions aquatic species, they have escaped the demands of life on land (demands which place limitations on the ornateness of body form that can develop).
Crustaceans are an old group of animals, dating back some 500 million years to the Cambrian. Their body plan is simple yet elegant and adaptable. In his book, The Variety of Life, Colin Tudge likens crustaceans to mobile Swiss Army knives—composed of up to 32 segments each equipped with its own pair of appendages that are modified for a variety of tasks: locomotion, defense, communication, feeding, hunting, reproduction. Each segment and its appendage is like a separate tool and together the segments and appendages form as well-adapted a tool kit as a Swiss Army knife.
Photo © Ben Cranke / Getty Images.
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