shrimp a term which always refers to certain crustaceans, to wit those in the sub-order Natantia (swimmers) in the order Decapoda Crustacea (ten-footed crustaceans), but which, with the associated term ‘prawn’, is used in different ways on the two sides of the Atlantic— and in other parts of the world, depending on whether use of the English language has been influenced by the British or by Americans. Since the FAO (Food and Agriculture Organization of the United Nations) has taken the trouble to produce a comprehensive Catalogue of Shrimps and Prawns of the World (Holthuis, 1980), they may be allowed to explain:
we may say that in Great Britain the term ‘shrimp’ is the more general of the two, and is the only term used for Crangonidae and most smaller species. ‘Prawn’ is the more special of the two names, being used solely for Palaemonidae and larger forms, never for the very small ones.
In North America the name ‘prawn’ is practically obsolete and is almost entirely replaced by the word ‘shrimp’ (used for even the largest species, which may be called ‘jumbo shrimp’). If the word ‘prawn’ is used at all in America it is attached to small species.