Three views of a beach hopper. Unfortunately, I don't know what species this is, but I couldn't resist posting the photos — their blue antennae and legs are so intriguing!
If you've spent any time on the upper beach, especially at dusk or at night, you've probably encountered beach hoppers. Formally, they're talitrid amphipods, shrimp-like crustaceans that are laterally compressed.
Note the large compound eyes, long antennae, and well-developed legs. When walking, the posterior legs are held out to the side for stability (see third photo). Beach hoppers are capable of very impressive jumps. The jump is achieved by curling under the end of the abdomen and then straightening it suddenly, which launches the animal into the air. They'll often start jumping randomly to avoid predators (and may even feign death at the end of a series of jumps).
When not out feeding, beach hoppers burrow below the surface of the sand or find shelter under seaweed and other materials in the wrack line. It's worth taking a closer look at them, and marveling at their saltatory abilities!