Shrimp belong to the Invertebrates and therein to the phylum Arthropoda, the anthropods. They are with a hard exoskeleton and articulated legs that have to shed, or moult, their shell from time to time in order to grow. They are the largest group with more than 800,000 described species.
Within the arthropods, shrimp belong to the Crustacea (crustaceans) class and therein again to the Decapoda (ten legs) order. Finally, this order is again subdivided into the Reptantia (walking decapods) and Natantia (swimming decapods) suborders. Shrimp are classed as belonging to this last suborder.
Although shrimp, lobsters and crabs are related to each other (they all belong to the Decapoda order) there is one important difference. Crabs and lobsters all have legs under their anterior thorax (thoracopods) with which they can crawl. Shrimp also have a set of swimming legs (pleopods; tiny, feathery swimmerets found on their abdomen) which allows them to swim. This is the most striking fundamental difference between shrimp and lobsters. There are more than two thousand species of shrimp that we know. By no means are all species, however, utilised commercially. Many tropical species are, it is true, fished and processed but without the species being explicitly important as such. The reason is that once the shrimp have been peeled they look alike and are interchangeable gastronomically. Commercially, we are interested in these species, mainly, because of their size and sometimes the specific species is completely unimportant. This leads to there being quite a large number of ‘species’, seen from a taxonomical point of view, in the European industry; the number of species that have been identified by name can be easily reviewed.
