The decapods or Decapoda are a group of crustaceans within the class Malacostraca, including many familiar groups of crustaceans, such as crabs, lobsters and shrimp, but also some families that are less well known.
Full article : Decapod anatomy
As their name implies, all decapods have ten legs; these are the last five of the eight pairs of thoracic appendages characteristic of crustaceans. The front three pairs function as mouthparts and are generally referred to as maxillipeds, the remainder being pereiopods. In many decapods, however, one pair of legs has enlarged pincers; the claws are called chelae, so those legs may be called chelipeds. Further appendages are found on the abdomen, with each segment capable of carrying a pair of biramous pleopods, the last of which form part of the tail fan (together with the telson) and are called uropods.
Classification within the Decapoda makes use of the structure of the gills and legs, and the way in which the larvae develop, giving rise to two suborders: Dendrobranchiata and Pleocyemata. Prawns (including many species colloquially referred to as "shrimp", such as the Atlantic white shrimp) make up the Dendrobranchiata. The remaining groups, including true shrimp, are the Pleocyemata.