Description: A burrowing crab with a distinctly shaped elongated, oval carapace that allows the crab to easily slide into the sand. Carapace up to 5 cm long. It has long bristled antennae between the eyes, which can be held together to create a breathing tube that can draw in clean water when the crab is buried. These are always longer than the width of the carapace. Tips of these antennae may be all that is seen poking out of the sand whilst the crab is buried. Relatively short walking legs, males have very long-clawed front legs (chelipeds). These are of equal size and always longer than the walking legs in both sexes. Its common name of ‘masked’ crab comes from the distinctive grooves and ridges on the carapace which are said to look like a mask or human face.

Habitat: Sandy substrate from lower shore to around 100 m sublittoral.

Distribution: Widespread around the UK and Ireland.

Similar Species: Unlikely to be confused with any other species. Long antennae and body shape distinctive.

Key Identification Features:

• Long, bristled antennae between eyes.
• Distinctly shaped elongated, oval carapace.
• Males have extremely long front claws.
• Distinctive ridges on carapace look like a mask or face.

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

iNaturalist: Corystes cassivelaunus at iNaturalist World Species Observations database.

WoRMS: Corystes cassivelaunus at World Register of Marine Species. Accepted name: Corystes cassivelaunus (Pennant, 1777). AphiaID: 107277.

Classification: Biota; Animalia; Arthropoda; Crustacea; Multicrustacea; Malacostraca; Eumalacostraca; Eucarida; Decapoda; Pleocyemata; Brachyura; Eubrachyura; Heterotremata; Corystoidea; Corystidae; Corystes