This looks like a sandhopper to me, the name given to a group of small terrestrial crustaceans, sometimes also known as sand fleas. The name comes from the habit of hopping jumping on the sand when it is disturbed. The sandhopper has an almost shrimp-like shape and is about one and half to two centimetres in length. It is varies in colour but is generally brownish grey and has a long arched body that has seven segments. It has two pairs of antennae on the front of its head. One pair is quite long and the other pair is quite short. It also has two large round black eyes. During the day sandhoppers generally hide buried in the sand (up to thirty centimetres down) and emerge early evening and at night. They can often be seen in large groups on the sand, especially where seaweed has been washed up on the shore. Sandhoppers feed on decaying seaweed or decaying algae.