A shrimp (: shrimp (US) or shrimps (UK)) is a common name typically used for crustaceans with an elongated body and a primarily swimming mode of locomotion. The name usually refers to decapods belonging to the Caridea or Dendrobranchiata, although some crustaceans outside this order are also referred to as "shrimp".
More narrow definitions may be restricted to Caridea, to smaller species of either of the aforementioned groups, or only the marine species. Under a broader definition, shrimp may be synonymous with prawn, covering stalk-eyed swimming crustaceans with long, narrow muscular tails (abdomens), long whiskers (antennae), and slender, biramous legs.Shrimp Encyclopædia Britannica. Retrieved 20 August 2012. They swim forward by paddling the swimmerets on the underside of their abdomens, although their escape response is typically repeated flicks with the tail, driving them backwards very quickly ("lobstering"). Crabs and lobsters have strong walking legs, whereas shrimp typically have thin, fragile legs which they use primarily for perching.Rudloe & Rudloe (2009), pp. 15–26.
Shrimp are widespread and abundant. There are thousands of species adapted to a wide range of habitats, both freshwater and marine; they can be found feeding near the seafloor on most coasts and estuaries, as well as in rivers and lakes. They play important roles in the food chain and are an important food source for larger animals ranging from fish to whales; 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.
Being one of the more popular shellfish eaten, the muscular tails of many forms of shrimp are eaten by humans, and they are widely caught or farmed for human consumption. It is estimated that about 440 billion farmed shrimp, and about 25 trillion wild shrimp, are slaughtered annually. Excessive bycatch and overfishing (from wild shrimperies) is a significant concern, and waterbodies may suffer from pollution when they are used to support shrimp farming.
Classification Shrimp vis-à-vis prawn
The terms shrimp and prawn are common names, not scientific names. They are vernacular or colloquial terms, which lack the formal definition of scientific terms. They are not taxa, but are terms of convenience with little circumscriptional significance. There is no reason to avoid using the terms shrimp or prawn when convenient, but it is important not to confuse them with the names or relationships of actual taxa.
According to the crustacean taxonomist Tin-Yam Chan, "The terms shrimp and prawn have no definite reference to any known taxonomic groups. Although the term shrimp is sometimes applied to smaller species, while prawn is more often used for larger forms, there is no clear distinction between both terms and their usage is often confused or even reverse in different countries or regions."Chan, TY (1998) Shrimps and prawns In K.E. Carpenter & V.H. Niem. The living marine resources of the western central Pacific. FAO species identification guide for fishery purposes. Rome, FAO. Writing in 1980, L. B. Holthuis noted that the terms prawn and shrimp were used inconsistently "even within a single region", generalising that larger species fished commercially were generally called shrimp in the United States, and prawns in other English-speaking countries, although not without exceptions.Holthuis, L. B. (1980) Shrimps and prawns of the world Volume I of the FAO species catalogue, Fisheries Synopsis No.125, Rome. .
Much confusion surrounds the scope of the term shrimp. Part of the confusion originates with the word's association with smallness; many shrimp species are small, about long, but some shrimp exceed , such as Penaeus monodon. The expression "jumbo shrimp" can be viewed as an oxymoron, a problem that does not exist with the commercial designation "jumbo prawns". Larger shrimp are more likely to be targeted commercially and are often referred to as prawns, particularly in the Commonwealth of Nations.
The term shrimp originated around the 14th century with the Middle English , akin to the Middle Low German , and meaning 'to contract or wrinkle'; and the Old Norse , meaning 'to shrivel up', or , meaning 'a thin person'. It is not clear where the term prawn originated, but early forms of the word surfaced in England in the early 15th century as prayne, praine and prane.prawnOnline Etymology Dictionary. Retrieved 5 August 2012.Prawn Merriam-Webster Dictionary. Retrieved 5 August 2012.Liberman, Anatoly (2012) After 'shrimp' comes 'prawn' Oxford University Press's Blog, 16 May 2012. According to the linguist Anatoly Liberman it is unclear how shrimp, in English, came to be associated with small, since no other language with Germanic origins associates shrimp with how large they are. "The same holds for Romance... it remains unclear in what circumstances the name was applied to the crustacean."Liberman, Anatoly (2012) A scrumptious shrimp with a riddle Oxford University Press's Blog, 18 April 2012.
Taxonomy Taxonomic studies in Europe on shrimp and prawns were shaped by the common shrimp and the common prawn, both found in huge numbers along the European coastlines. The common shrimp, Crangon crangon, was categorised in 1758 by Carl Linnaeus, and the common prawn, Palaemon serratus, was categorised in 1777 by Thomas Pennant. The common shrimp is a small burrowing species aligned with the notion of a shrimp as being something small, whereas the common prawn is much larger. The terms true shrimp or true prawn are sometimes used to mean what a particular person thinks is a shrimp or prawn. This varies with the person using the terms. But such terms are not normally used in the scientific literature, because the terms shrimp and prawn themselves lack scientific standing. Over the years the way shrimp and prawn are used has changed, and nowadays the terms are almost interchangeable. Although from time to time some biologists declare that certain common names should be confined to specific taxa, the popular use of these names seems to continue unchanged.
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.Bauer, 2004, Chapter 1, pp. 3–14. Some other groups also have common names that include the word "shrimp";Bauer, 2004, Chapter 2, pp. 15–35. any small swimming crustacean resembling a shrimp tends to be called one, and a number of small-bodied crustacean groups not resembling shrimp are also referred to as shrimp.Rudloe & Rudloe (2009)
Differences between shrimp, lobsters and crabs Shrimp are slender with long muscular abdomens. They look somewhat like small lobsters, but not like crabs. The abdomens of crabs are small and short, whereas the abdomens of lobsters and shrimp are large and long. The lower abdomens of shrimp support pleopods which are well-adapted for swimming. The carapaces of crabs are wide and flat, whereas the carapaces of lobsters and shrimp are more cylindrical. The antennae of crabs are short, whereas the antennae of lobsters and shrimp are usually long, reaching more than twice the body length in some shrimp species.Mortenson, Philip B (2010) This is not a weasel: a close look at nature's most confusing terms Pages 106–109, John Wiley & Sons. . Clawed lobsters (pictured left) and spiny lobsters (pictured right) are an intermediate evolutionary development between shrimp and crabs. They look somewhat like large versions of shrimp. Clawed lobsters have large claws while spiny lobsters do not, having instead spiny antennae and carapace. Some of the biggest decapods are lobsters. Like crabs, lobsters have robust legs and are highly adapted for walking on the seafloor, though they do not walk sideways. Some species have rudimentary pleopods, which give them some ability to swim, and like shrimp they can lobster with their tail to escape predators, but their primary mode of locomotion is walking, not swimming. Crabs evolved from early shrimp, though they do not look like shrimp. Unlike shrimp, their abdomens are small, and they have short antennae and short carapaces that are wide and flat. They have prominent grasping claws as their front pair of limbs. Crabs are adapted for walking on the seafloor. They have robust legs and usually move about the seafloor by walking sideways. They have pleopods, but they use them as intromittent organs or to hold egg broods, not for swimming. Whereas shrimp and lobsters escape predators by lobstering, crabs cling to the seafloor and burrow into sediment. Compared to shrimp and lobsters, the carapaces of crabs are particularly heavy, hard and mineralized.Ruppert et al. (2004), pp. 628–650.Ward, Peter (2006) Out of Thin Air: Dinosaurs, Birds, and Earth's Ancient Atmosphere page 219, National Academies Press. .
Fossils Only 57 exclusively fossil species are known in the shrimp fossil record. The earliest dates from the Lower Jurassic, followed by specimens from the Cretaceous.
Description
The following description refers mainly to the external anatomy of the common European shrimp, Crangon crangon, as a typical example of a decapod shrimp. The body of the shrimp is divided into two main parts: the head and thorax which are fused together to form the cephalothorax, and a long narrow abdomen. The shell which protects the cephalothorax is harder and thicker than the shell elsewhere on the shrimp and is called the carapace. The carapace typically surrounds the gills, through which water is pumped by the action of the mouthparts. The rostrum, eyes, whiskers and legs also issue from the carapace. The rostrum, from the Latin rōstrum meaning beak, looks like a beak or pointed nose at the front of the shrimp's head. It is a rigid forward extension of the carapace and can be used for attack or defense. It may also stabilize the shrimp when it swims backward. Two bulbous eyes on stalks sit either side of the rostrum. These are compound eyes which have panoramic vision and are very good at detecting movement. Two pairs of whiskers (antennae) also issue from the head. One of these pairs is very long and can be twice the length of the shrimp, while the other pair is quite short. The antennae have sensors on them which allow the shrimp to feel where they touch, and also allow them to "smell" or "taste" things by sampling the chemicals in the water. The long antennae help the shrimp orient itself with regard to its immediate surroundings, while the short antennae help assess the suitability of prey.
Eight pairs of appendages issue from the cephalothorax. The first three pairs, the maxillipeds, Latin for "jaw feet", are used as mouthparts. In Crangon crangon, the first pair, the maxillula, pumps water into the gill cavity. After the maxilliped come five more pairs of appendages, the pereiopods. These form the ten decapod legs. In Crangon crangon, the first two pairs of pereiopods have claws or chela. The chela can grasp food items and bring them to the mouth. They can also be used for fighting and grooming. The remaining four legs are long and slender, and are used for walking or perching.Decapod Encyclopædia Britannica. Retrieved 20 August 2012.