The term shrimp is used to refer to some decapod crustaceans, although the exact animals covered can vary. Used broadly, it may cover any of the groups with elongated bodies and a primarily swimming mode of locomotion – chiefly Caridea and Dendrobranchiata. In some fields, however, the term is used more narrowly, and may be restricted to Caridea, to smaller species of either group, or to only the marine species. Under the broader definition, shrimp may be synonymous with prawn, covering stalk-eyed swimming crustaceans with long narrow muscular tails (abdomens), long whiskers (antennae) and slender legs. They swim forwards by paddling with swimmerets on the underside of their abdomens. Crabs and lobsters have strong walking legs, whereas shrimp have thin fragile legs which they use primarily for perching.
Shrimp are widespread and abundant. They can be found feeding near the seafloor on most coasts and estuaries, as well as in rivers and lakes. To escape predators, some species flip off the seafloor and dive into the sediment. They usually live from one to seven years. Shrimp are often solitary, though they can form large schools during the spawning season. There are thousands of species, and usually there is a species adapted to any particular habitat. Any small crustacean which resembles a shrimp tends to be called one.
Behavior
There are many variations in the ways different types of shrimp look and behave. Even within the core group of caridean shrimp, the small delicate Pederson's shrimp (above) looks and behaves quite unlike the large commercial pink shrimp or the snapping pistol shrimp. The caridean family of pistol shrimp are characterized by big asymmetrical claws, the larger of which can produce a loud snapping sound. The family is diverse and worldwide in distribution, consisting of about 600 species. Colonies of snapping shrimp are a major source of noise in the ocean and can interfere with sonar and underwater communication. The small emperor shrimp has a symbiotic relationship with sea slugs and sea cucumbers, and may help keep them clear of ectoparasites.
Classification
Shrimp are swimming crustaceans with long narrow muscular abdomens and long antennae. Unlike crabs and lobsters, shrimp have well developed pleopods (swimmerets) and slender walking legs; they are more adapted for swimming than walking. Historically, it was the distinction between walking and swimming that formed the primary taxonomic division into the former suborders Natantia and Reptantia. Members of the Natantia (shrimp in the broader sense) were adapted for swimming while the Reptantia (crabs, lobsters, etc.) were adapted for crawling or walking. Some other groups also have common names that include the word "shrimp"; any small swimming crustacean resembling a shrimp tends to be called one.
