Liocarcinus marmoreus, sometimes known as the marbled swimming crab, is a species of crab found in the northern Atlantic Ocean and North Sea. It may be found on sand and gravel in the sublittoral and lower littoral zones, down to a depth of 84 metres (276 ft), from the Azores and the Alboran Sea (the westernmost section of the Mediterranean Sea) as far north as the Shetland Islands. It reaches a carapace length of 35 millimetres (1.4 in), and is distinguished from other similar species by the presence of three similarly-sized teeth on the edge of the carapace, between the eyes, and by the marbled colouration on the carapace. L. marmoreus is sometimes parasitised by the barnacle Sacculina.