Prawn and shrimp are not the same
While prawns and shrimps are two totally separate groups of life forms with several different species in each group, many people freely interchange the two names giving the impression that they are identical creatures.
Matters are not helped by the fact that some prawns were given English names that contained the word 'shrimp' and vice versa. The creature featured in the image above is known in books about the seashore as the Common Prawn, but it is in fact a shrimp.
Some people add to the confusion by claiming that it is simply a matter of size: they call the big ones prawns and the small ones shrimps. No so; some prawns are small, and some shrimps are big, so size is not the best indicator.
And then there is the cultural difference. On this side of the Atlantic we tend to use the umbrella term 'prawn' for both of them while Americans tend to say 'shrimp' where we would say prawn.
From a cooking point of view both prawns and shrimps are treated in very much the same way. There is, of course, a difference in taste; prawns are sweeter, more succulent and more like chicken while shrimps are butterier.
In appearance, prawns generally have a more smoothly-curving, rounded and tapering back whereas shrimps have more or an L-shaped back with an angle midships dividing the back into two distinct parts and allowing them to curl tightly.
Both prawns and shrimps have ten legs. The front five are used for walking, the hind five are used for swimming. Prawns tend to have longer walking legs and have claws on three pairs of them whereas shrimps have claws on only two pairs of their shorter walking legs.
These clawed walking legs are clearly visible on the creature featured in the image above. There are two of them indicating that the owner is a shrimp. Unfortunately, though it is the common on rocky seashores all around Ireland, it is popularly known as the Common Prawn.
Crabs, lobsters, crayfish, and their allies are all closely related to true shrimps. Prawns are a distinct group.
The biological differences between prawns and shrimps lie in the structure of their gills and how their eggs are brooded. Prawns have branched gills whereas shrimps have plate-like ones. Prawns release their eggs into the sea without any brooding whereas female shrimps incubate them under their bodies until they hatch.