Prawns are crustaceans, belonging to the sub-order Dendrobranchiata . They are similar in appearance to shrimp, but can be distinguished by the gill structure which is branching in prawns (hence the name, dendro=“tree”; branchia=“gill”), but is lamellar in shrimp. The sister taxon to Dendrobranchiata is Pleocyemata, which contains all the true shrimp, crabs, lobsters, etc.
In various forms of English, the name “prawn” is often applied to shrimp as well, generally the larger species, such as Leander serratus. In the United States, according to the 1911 Encyclopædia Britannica, the word “prawn” usually indicates a freshwater shrimp or prawn. In Middle English, the word “prawn” is recorded as prayne or prane; no cognate form can be found in any other language. It has often been connected to the Latin perna, a ham-shaped shellfish, but this is due to an old scholarly error that connected perna and parnocchie with prawne-fishes or shrimps. In fact, the Old Italian perna and pernocchia meant a shellfish that yielded nacre, or mother-of-pearl.