Description: Medium-sized swimming crab (reaching around 35 mm) with a smooth carapace of varied marbled coloration, sometimes displaying striking red-brown and white banding. Pincers and legs are paler in colour and the paddle on the fifth set of legs is blue. Frontal lobe has three small, even teeth. Five teeth on either side of carapace, the first two are slightly rounded, the third to fifth are more pointed. Stout, equally-sized pincers.

Habitat: Fine sand and gravel, from lower shore down to around 200m.

Distribution: Found on all coasts of Britain and Ireland, although not common. Very few records from north and east coasts of Ireland, and not commonly recorded in Irish Sea.

Similar Species: Could be confused with other Polybius sp

Key Identification Features:

• Marbled colouration of smooth carapace, sometimes quite striking.
• Three small, even teeth on frontal lobe.
• Five teeth either side of carapace, the first two more rounded and last three much more pointed.

Distribution Map from NBN: Polybius marmoreus at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Polybius marmoreus at iNaturalist World Species Observations database.

WoRMS: Polybius marmoreus at World Register of Marine Species. Accepted name: Polybius marmoreus (Leach, 1814). AphiaID: 1750287.

Classification: Biota; Animalia; Arthropoda; Crustacea; Multicrustacea; Malacostraca; Eumalacostraca; Eucarida; Decapoda; Pleocyemata; Brachyura; Eubrachyura; Heterotremata; Portunoidea; Polybiidae; Polybius