Polybius marmoreus

Polybius marmoreus, sometimes known as the marbled swimming crab, is a species of crab found in the northern Atlantic Ocean, including the Mediterranean Sea and North Sea. It may be found on sand and gravel in the sublittoral and lower littoral zones, down to a depth of, from the Azores and the Alboran Sea as far north as the Shetland Islands. It reaches a carapace length of, 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. P. marmoreus is sometimes parasitised by the barnacle Sacculina.