The pennant's swimming crab is common along the shorelines of the North Sea. Just like the flying crab and the velvet swimming crab, it is a good swimmer with back legs that have flattened into paddles. However, the back legs of the pennant's swimming crab are much smaller than those of the other species. It can dig itself into wet sand very rapidly. The paddles serve for digging sand. It is easy to identify a pennant's swimming crab by the white spot(s) often found on its back.