Spotty crab

Finn discovered this little gem and all of us were perplexed. The closest we could get to an identification was to say that maybe it was a shore crab with a disease or a parasite. The only problem was that the patterns were so balanced and uniform. A tidy, symetrical parasite? In the end after looking in loads of books and on the internet I called Cornwall Wildlife Trust. They suggested I send over a photo and this is what we discovered....

Further to our conversation the other day regarding the strange crab you found at Mevagissey recently; thank you for your excellent photograph. I can confirm that this is indeed a juvenile Shore Crab ( Carcinus maenas). Juvenile Shore Crabs can be a confusing variety of colours, since they adapt to the particular habitat they have been maturing in. As in your picture, they often develop white patches on the carapace to breakup their outline against shell and gravel. I hope this solves the mystery!I do hope that is of some help and please do contact us again if we can be of any more assistance in the future.  Yours,
John Rance-Wildlife Information Service