A typical prawn Illustration: Jo Taylor / Source: Museum Victoria
An important difference is in the way the segments of the abdomen (tail) overlap. In prawns the sides of all segments overlap the segment behind, like roof tiles. In shrimps the sides of the second segment overlap both the one before and the one after.
But that's not all....A shrimp in the USA is a prawn in Australia. WHAT!
more info @ http://museumvictoria.com.au/discoverycentre/