It's true that prawns and shrimp are very similar in appearance, taste, and uses, but they are not the same critter--in fact they are completely different species. Shrimp are among several thousand species in the suborder Pleocyemata (remember biology class?), while prawns fall under the suborder Dendrobranchiata, which also has several thousand species. The most obvious difference between them is that prawns are larger than shrimp, with prawns generally over 4 inches in length and shrimp smaller.