Haven't we done the prawn/shrimp distinction before?

In those parts of the world where the words are not used interchangeably, the distinction is drawn mainly by size. The trouble is that, in some parts of the world, the big ones are prawns and the little ones are shrimps, while, in other parts of the world, the big ones are shrimps and the little ones are prawns. This sounds like something Lewis Carroll might have contrived.