I'm afraid Suzanne wasn't too much off with her first impression of "shrimp like". We call these "Strandvlo" (Beach flea) - Talitridae - Wikipedia seems to think you call them Sand hopper
, but that may well be American English(?)
They're some of the rare Amphipod Crustacean that can be found semi-terrestrial on shores etc. Some even have made it as far as living mostly on land, I think one or two species can even be found in gardens, but if I'm informed correctly these will still need a puddle or water of some sort te reproduce (unlike woodlice).
The one found on sea shores could very well be Talitrus saltator
, but that's not an ID - I don't know the first thing about these except that I find them often when hunting for littoral woodlice (such as the Ligia
suggested by Paul).
The Sea Slater (not skater - maybe why you had trouble finding info?) is much larger (or at least adults are - up to 3cm) and is flattened dorsally, whereas these "beach shrimps" are flattened laterally.
Here is Ligia oceanica